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diff --git a/doc/flex.info-1 b/doc/flex.info-1 index da0d581..2131353 100644 --- a/doc/flex.info-1 +++ b/doc/flex.info-1 @@ -1,14 +1,16 @@ -This is flex.info, produced by makeinfo version 4.5 from flex.texi. +This is flex.info, produced by makeinfo version 4.8 from flex.texi. INFO-DIR-SECTION Programming START-INFO-DIR-ENTRY * flex: (flex). Fast lexical analyzer generator (lex replacement). END-INFO-DIR-ENTRY - The flex manual is placed under the same licensing conditions as the rest of flex: + Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007 The Flex +Project. + Copyright (C) 1990, 1997 The Regents of the University of California. All rights reserved. @@ -30,6 +32,7 @@ met: notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. + Neither the name of the University nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. @@ -37,18 +40,21 @@ without specific prior written permission. THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. + File: flex.info, Node: Top, Next: Copyright, Prev: (dir), Up: (dir) flex **** - This manual describes `flex', a tool for generating programs that +This manual describes `flex', a tool for generating programs that perform pattern-matching on text. The manual includes both tutorial and reference sections. - This edition of `The flex Manual' documents `flex' version 2.5.33. -It was last updated on 20 February 2006. + This edition of `The flex Manual' documents `flex' version 2.5.34. +It was last updated on 10 September 2007. + + This manual was written by Vern Paxson, Will Estes and John Millaway. * Menu: @@ -92,7 +98,7 @@ Format of the Input File Scanner Options -* Options for Specifing Filenames:: +* Options for Specifying Filenames:: * Options Affecting Scanner Behavior:: * Code-Level And API Options:: * Options for Scanner Speed and Size:: @@ -132,7 +138,7 @@ Serialized Tables FAQ * When was flex born?:: -* How do I expand \ escape sequences in C-style quoted strings?:: +* How do I expand backslash-escape sequences in C-style quoted strings?:: * Why do flex scanners call fileno if it is not ANSI compatible?:: * Does flex support recursive pattern definitions?:: * How do I skip huge chunks of input (tens of megabytes) while using flex?:: @@ -145,9 +151,9 @@ FAQ * Why cant I use fast or full tables with interactive mode?:: * How much faster is -F or -f than -C?:: * If I have a simple grammar cant I just parse it with flex?:: -* Why doesnt yyrestart() set the start state back to INITIAL?:: +* Why doesn't yyrestart() set the start state back to INITIAL?:: * How can I match C-style comments?:: -* The period isnt working the way I expected.:: +* The period isn't working the way I expected.:: * Can I get the flex manual in another format?:: * Does there exist a "faster" NDFA->DFA algorithm?:: * How does flex compile the DFA so quickly?:: @@ -165,7 +171,7 @@ FAQ * I am trying to port code from AT&T lex that uses yysptr and yysbuf.:: * Is there a way to make flex treat NULL like a regular character?:: * Whenever flex can not match the input it says "flex scanner jammed".:: -* Why doesnt flex have non-greedy operators like perl does?:: +* Why doesn't flex have non-greedy operators like perl does?:: * Memory leak - 16386 bytes allocated by malloc.:: * How do I track the byte offset for lseek()?:: * How do I use my own I/O classes in a C++ scanner?:: @@ -239,6 +245,7 @@ Appendices * Makefiles and Flex:: * Bison Bridge:: * M4 Dependency:: +* Common Patterns:: Indices @@ -252,13 +259,15 @@ Indices File: flex.info, Node: Copyright, Next: Reporting Bugs, Prev: Top, Up: Top -Copyright -********* - +1 Copyright +*********** - The flex manual is placed under the same licensing conditions as the +The flex manual is placed under the same licensing conditions as the rest of flex: + Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007 The Flex +Project. + Copyright (C) 1990, 1997 The Regents of the University of California. All rights reserved. @@ -280,6 +289,7 @@ met: notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. + Neither the name of the University nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. @@ -287,23 +297,24 @@ without specific prior written permission. THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. + File: flex.info, Node: Reporting Bugs, Next: Introduction, Prev: Copyright, Up: Top -Reporting Bugs -************** +2 Reporting Bugs +**************** - If you have problems with `flex' or think you have found a bug, -please send mail detailing your problem to -<flex-help@lists.sourceforge.net>. Patches are always welcome. +If you find a bug in `flex', please report it using the SourceForge Bug +Tracking facilities which can be found on flex's SourceForge Page +(http://sourceforge.net/projects/flex). File: flex.info, Node: Introduction, Next: Simple Examples, Prev: Reporting Bugs, Up: Top -Introduction -************ +3 Introduction +************** - `flex' is a tool for generating "scanners". A scanner is a program +`flex' is a tool for generating "scanners". A scanner is a program which recognizes lexical patterns in text. The `flex' program reads the given input files, or its standard input if no file names are given, for a description of a scanner to generate. The description is @@ -318,10 +329,10 @@ corresponding C code. File: flex.info, Node: Simple Examples, Next: Format, Prev: Introduction, Up: Top -Some Simple Examples -******************** +4 Some Simple Examples +********************** - First some simple examples to get the flavor of how one uses `flex'. +First some simple examples to get the flavor of how one uses `flex'. The following `flex' input specifies a scanner which, when it encounters the string `username' will replace it with the user's login @@ -342,11 +353,11 @@ rules. int num_lines = 0, num_chars = 0; - + %% \n ++num_lines; ++num_chars; . ++num_chars; - + %% main() { @@ -368,43 +379,43 @@ other than a newline (indicated by the `.' regular expression). /* scanner for a toy Pascal-like language */ - + %{ /* need this for the call to atof() below */ #include math.h> %} - + DIGIT [0-9] ID [a-z][a-z0-9]* - + %% - + {DIGIT}+ { printf( "An integer: %s (%d)\n", yytext, atoi( yytext ) ); } - + {DIGIT}+"."{DIGIT}* { printf( "A float: %s (%g)\n", yytext, atof( yytext ) ); } - + if|then|begin|end|procedure|function { printf( "A keyword: %s\n", yytext ); } - + {ID} printf( "An identifier: %s\n", yytext ); - + "+"|"-"|"*"|"/" printf( "An operator: %s\n", yytext ); - + "{"[\^{}}\n]*"}" /* eat up one-line comments */ - + [ \t\n]+ /* eat up whitespace */ - + . printf( "Unrecognized character: %s\n", yytext ); - + %% - + main( argc, argv ) int argc; char **argv; @@ -414,7 +425,7 @@ other than a newline (indicated by the `.' regular expression). yyin = fopen( argv[0], "r" ); else yyin = stdin; - + yylex(); } @@ -428,11 +439,11 @@ sections. File: flex.info, Node: Format, Next: Patterns, Prev: Simple Examples, Up: Top -Format of the Input File -************************ +5 Format of the Input File +************************** - The `flex' input file consists of three sections, separated by a -line containing only `%%'. +The `flex' input file consists of three sections, separated by a line +containing only `%%'. definitions @@ -451,10 +462,10 @@ line containing only `%%'. File: flex.info, Node: Definitions Section, Next: Rules Section, Prev: Format, Up: Format -Format of the Definitions Section -================================= +5.1 Format of the Definitions Section +===================================== - The "definitions section" contains declarations of simple "name" +The "definitions section" contains declarations of simple "name" definitions to simplify the scanner specification, and declarations of "start conditions", which are explained in a later section. @@ -519,11 +530,11 @@ included before the generated code. The single characters, `{' and File: flex.info, Node: Rules Section, Next: User Code Section, Prev: Definitions Section, Up: Format -Format of the Rules Section -=========================== +5.2 Format of the Rules Section +=============================== - The "rules" section of the `flex' input contains a series of rules -of the form: +The "rules" section of the `flex' input contains a series of rules of +the form: pattern action @@ -548,21 +559,21 @@ and %} symbols must appear unindented on lines by themselves. File: flex.info, Node: User Code Section, Next: Comments in the Input, Prev: Rules Section, Up: Format -Format of the User Code Section -=============================== +5.3 Format of the User Code Section +=================================== - The user code section is simply copied to `lex.yy.c' verbatim. It -is used for companion routines which call or are called by the scanner. +The user code section is simply copied to `lex.yy.c' verbatim. It is +used for companion routines which call or are called by the scanner. The presence of this section is optional; if it is missing, the second `%%' in the input file may be skipped, too. File: flex.info, Node: Comments in the Input, Prev: User Code Section, Up: Format -Comments in the Input -===================== +5.4 Comments in the Input +========================= - Flex supports C-style comments, that is, anything between /* and */ +Flex supports C-style comments, that is, anything between `/*' and `*/' is considered a comment. Whenever flex encounters a comment, it copies the entire comment verbatim to the generated source code. Comments may appear just about anywhere, but with the following exceptions: @@ -585,10 +596,10 @@ new line, with one or more whitespace characters before the initial %{ /* code block */ %} - + /* Definitions Section */ %x STATE_X - + %% /* Rules Section */ ruleA /* after regex */ { /* code block */ } /* after code block */ @@ -606,11 +617,11 @@ new line, with one or more whitespace characters before the initial File: flex.info, Node: Patterns, Next: Matching, Prev: Format, Up: Top -Patterns -******** +6 Patterns +********** - The patterns in the input (see *Note Rules Section::) are written -using an extended set of regular expressions. These are: +The patterns in the input (see *Note Rules Section::) are written using +an extended set of regular expressions. These are: `x' match the character 'x' @@ -633,6 +644,9 @@ using an extended set of regular expressions. These are: `[^A-Z\n]' any character EXCEPT an uppercase letter or a newline +`[a-z]{-}[aeiou]' + the lowercase consonants + `r*' zero or more r's, where r is any regular expression @@ -675,6 +689,43 @@ using an extended set of regular expressions. These are: match an `r'; parentheses are used to override precedence (see below) +`(?r-s:pattern)' + apply option `r' and omit option `s' while interpreting pattern. + Options may be zero or more of the characters `i', `s', or `x'. + + `i' means case-insensitive. `-i' means case-sensitive. + + `s' alters the meaning of the `.' syntax to match any single byte + whatsoever. `-s' alters the meaning of `.' to match any byte + except `\n'. + + `x' ignores comments and whitespace in patterns. Whitespace is + ignored unless it is backslash-escaped, contained within `""'s, or + appears inside a character class. + + The following are all valid: + + + (?:foo) same as (foo) + (?i:ab7) same as ([aA][bB]7) + (?-i:ab) same as (ab) + (?s:.) same as [\x00-\xFF] + (?-s:.) same as [^\n] + (?ix-s: a . b) same as ([Aa][^\n][bB]) + (?x:a b) same as ("ab") + (?x:a\ b) same as ("a b") + (?x:a" "b) same as ("a b") + (?x:a[ ]b) same as ("a b") + (?x:a + /* comment */ + b + c) same as (abc) + +`(?# comment )' + omit everything within `()'. The first `)' character encountered + ends the pattern. It is not possible to for the comment to contain + a `)' character. The comment may span lines. + `rs' the regular expression `r' followed by the regular expression `s'; called "concatenation" @@ -780,7 +831,11 @@ any alphabetic or numeric character. Some systems don't provide [[:alpha:][0-9]] [a-zA-Z0-9] - Some notes on patterns are in order. + A word of caution. Character classes are expanded immediately when +seen in the `flex' input. This means the character classes are +sensitive to the locale in which `flex' is executed, and the resulting +scanner will not be sensitive to the runtime locale. This may or may +not be desirable. * If your scanner is case-insensitive (the `-i' flag), then `[:upper:]' and `[:lower:]' are equivalent to `[:alpha:]'. @@ -813,6 +868,34 @@ any alphabetic or numeric character. Some systems don't provide can match the entire input unless there's another quote in the input. + Flex allows negation of character class expressions by prepending + `^' to the POSIX character class name. + + + [:^alnum:] [:^alpha:] [:^blank:] + [:^cntrl:] [:^digit:] [:^graph:] + [:^lower:] [:^print:] [:^punct:] + [:^space:] [:^upper:] [:^xdigit:] + + Flex will issue a warning if the expressions `[:^upper:]' and + `[:^lower:]' appear in a case-insensitive scanner, since their + meaning is unclear. The current behavior is to skip them entirely, + but this may change without notice in future revisions of flex. + + * The `{-}' operator computes the difference of two character + classes. For example, `[a-c]{-}[b-z]' represents all the + characters in the class `[a-c]' that are not in the class `[b-z]' + (which in this case, is just the single character `a'). The `{-}' + operator is left associative, so `[abc]{-}[b]{-}[c]' is the same + as `[a]'. Be careful not to accidentally create an empty set, + which will never match. + + * The `{+}' operator computes the union of two character classes. + For example, `[a-z]{+}[0-9]' is the same as `[a-z0-9]'. This + operator is useful when preceded by the result of a difference + operation, as in, `[[:alpha:]]{-}[[:lower:]]{+}[q]', which is + equivalent to `[A-Zq]' in the "C" locale. + * A rule can have at most one instance of trailing context (the `/' operator or the `$' operator). The start condition, `^', and `<<EOF>>' patterns can only occur at the beginning of a pattern, @@ -850,10 +933,10 @@ any alphabetic or numeric character. Some systems don't provide File: flex.info, Node: Matching, Next: Actions, Prev: Patterns, Up: Top -How the Input Is Matched -************************ +7 How the Input Is Matched +************************** - When the generated scanner is run, it analyzes its input looking for +When the generated scanner is run, it analyzes its input looking for strings which match any of its patterns. If it finds more than one match, it takes the one matching the most text (for trailing context rules, this includes the length of the trailing part, even though it @@ -920,11 +1003,11 @@ too much text being pushed back; instead, a run-time error results. File: flex.info, Node: Actions, Next: Generated Scanner, Prev: Matching, Up: Top -Actions -******* +8 Actions +********* - Each pattern in a rule has a corresponding "action", which can be -any arbitrary C statement. The pattern ends at the first non-escaped +Each pattern in a rule has a corresponding "action", which can be any +arbitrary C statement. The pattern ends at the first non-escaped whitespace character; the remainder of the line is its action. If the action is empty, then when the pattern is matched the input token is simply discarded. For example, here is the specification for a program @@ -945,7 +1028,7 @@ single blank, and throws away whitespace found at the end of a line: [ \t]+ putchar( ' ' ); [ \t]+$ /* ignore this token */ - If the action contains a `}', then the action spans till the + If the action contains a `{', then the action spans till the balancing `}' is found, and the action may cross multiple lines. `flex' knows about C strings and comments and won't be fooled by braces found within them, but also allows actions to begin with `%{' and will @@ -993,11 +1076,11 @@ within an action: int word_count = 0; %% - + frob special(); REJECT; [^ \t\n]+ ++word_count; - Without the `REJECT', any occurences of `frob' in the input would + Without the `REJECT', any occurrences of `frob' in the input would not be counted as words, since the scanner normally executes only one action per token. Multiple uses of `REJECT' are allowed, each one finding the next best choice to the currently active rule. For @@ -1022,7 +1105,7 @@ within an action: Scanner Options::). Note also that unlike the other special actions, `REJECT' is a - _branch_. code immediately following it in the action will _not_ + _branch_. Code immediately following it in the action will _not_ be executed. `yymore()' @@ -1105,13 +1188,13 @@ example, the following is one way to eat up C comments: %% "/*" { register int c; - + for ( ; ; ) { while ( (c = input()) != '*' && c != EOF ) ; /* eat up text of comment */ - + if ( c == '*' ) { while ( (c = input()) == '*' ) @@ -1119,7 +1202,7 @@ example, the following is one way to eat up C comments: if ( c == '/' ) break; /* found the end */ } - + if ( c == EOF ) { error( "EOF in comment" ); @@ -1147,10 +1230,10 @@ redefined. File: flex.info, Node: Generated Scanner, Next: Start Conditions, Prev: Actions, Up: Top -The Generated Scanner -********************* +9 The Generated Scanner +*********************** - The output of `flex' is the file `lex.yy.c', which contains the +The output of `flex' is the file `lex.yy.c', which contains the scanning routine `yylex()', a number of tables used by it for matching tokens, and a number of auxiliary routines and macros. By default, `yylex()' is declared as follows: @@ -1252,3 +1335,6349 @@ the default version of the routine, which always returns 1. `stdout'), which may be redefined by the user simply by assigning it to some other `FILE' pointer. + +File: flex.info, Node: Start Conditions, Next: Multiple Input Buffers, Prev: Generated Scanner, Up: Top + +10 Start Conditions +******************* + +`flex' provides a mechanism for conditionally activating rules. Any +rule whose pattern is prefixed with `<sc>' will only be active when the +scanner is in the "start condition" named `sc'. For example, + + + <STRING>[^"]* { /* eat up the string body ... */ + ... + } + + will be active only when the scanner is in the `STRING' start +condition, and + + + <INITIAL,STRING,QUOTE>\. { /* handle an escape ... */ + ... + } + + will be active only when the current start condition is either +`INITIAL', `STRING', or `QUOTE'. + + Start conditions are declared in the definitions (first) section of +the input using unindented lines beginning with either `%s' or `%x' +followed by a list of names. The former declares "inclusive" start +conditions, the latter "exclusive" start conditions. A start condition +is activated using the `BEGIN' action. Until the next `BEGIN' action +is executed, rules with the given start condition will be active and +rules with other start conditions will be inactive. If the start +condition is inclusive, then rules with no start conditions at all will +also be active. If it is exclusive, then _only_ rules qualified with +the start condition will be active. A set of rules contingent on the +same exclusive start condition describe a scanner which is independent +of any of the other rules in the `flex' input. Because of this, +exclusive start conditions make it easy to specify "mini-scanners" +which scan portions of the input that are syntactically different from +the rest (e.g., comments). + + If the distinction between inclusive and exclusive start conditions +is still a little vague, here's a simple example illustrating the +connection between the two. The set of rules: + + + %s example + %% + + <example>foo do_something(); + + bar something_else(); + + is equivalent to + + + %x example + %% + + <example>foo do_something(); + + <INITIAL,example>bar something_else(); + + Without the `<INITIAL,example>' qualifier, the `bar' pattern in the +second example wouldn't be active (i.e., couldn't match) when in start +condition `example'. If we just used `<example>' to qualify `bar', +though, then it would only be active in `example' and not in `INITIAL', +while in the first example it's active in both, because in the first +example the `example' start condition is an inclusive `(%s)' start +condition. + + Also note that the special start-condition specifier `<*>' matches +every start condition. Thus, the above example could also have been +written: + + + %x example + %% + + <example>foo do_something(); + + <*>bar something_else(); + + The default rule (to `ECHO' any unmatched character) remains active +in start conditions. It is equivalent to: + + + <*>.|\n ECHO; + + `BEGIN(0)' returns to the original state where only the rules with +no start conditions are active. This state can also be referred to as +the start-condition `INITIAL', so `BEGIN(INITIAL)' is equivalent to +`BEGIN(0)'. (The parentheses around the start condition name are not +required but are considered good style.) + + `BEGIN' actions can also be given as indented code at the beginning +of the rules section. For example, the following will cause the scanner +to enter the `SPECIAL' start condition whenever `yylex()' is called and +the global variable `enter_special' is true: + + + int enter_special; + + %x SPECIAL + %% + if ( enter_special ) + BEGIN(SPECIAL); + + <SPECIAL>blahblahblah + ...more rules follow... + + To illustrate the uses of start conditions, here is a scanner which +provides two different interpretations of a string like `123.456'. By +default it will treat it as three tokens, the integer `123', a dot +(`.'), and the integer `456'. But if the string is preceded earlier in +the line by the string `expect-floats' it will treat it as a single +token, the floating-point number `123.456': + + + %{ + #include <math.h> + %} + %s expect + + %% + expect-floats BEGIN(expect); + + <expect>[0-9]+@samp{.}[0-9]+ { + printf( "found a float, = %f\n", + atof( yytext ) ); + } + <expect>\n { + /* that's the end of the line, so + * we need another "expect-number" + * before we'll recognize any more + * numbers + */ + BEGIN(INITIAL); + } + + [0-9]+ { + printf( "found an integer, = %d\n", + atoi( yytext ) ); + } + + "." printf( "found a dot\n" ); + + Here is a scanner which recognizes (and discards) C comments while +maintaining a count of the current input line. + + + %x comment + %% + int line_num = 1; + + "/*" BEGIN(comment); + + <comment>[^*\n]* /* eat anything that's not a '*' */ + <comment>"*"+[^*/\n]* /* eat up '*'s not followed by '/'s */ + <comment>\n ++line_num; + <comment>"*"+"/" BEGIN(INITIAL); + + This scanner goes to a bit of trouble to match as much text as +possible with each rule. In general, when attempting to write a +high-speed scanner try to match as much possible in each rule, as it's +a big win. + + Note that start-conditions names are really integer values and can +be stored as such. Thus, the above could be extended in the following +fashion: + + + %x comment foo + %% + int line_num = 1; + int comment_caller; + + "/*" { + comment_caller = INITIAL; + BEGIN(comment); + } + + ... + + <foo>"/*" { + comment_caller = foo; + BEGIN(comment); + } + + <comment>[^*\n]* /* eat anything that's not a '*' */ + <comment>"*"+[^*/\n]* /* eat up '*'s not followed by '/'s */ + <comment>\n ++line_num; + <comment>"*"+"/" BEGIN(comment_caller); + + Furthermore, you can access the current start condition using the +integer-valued `YY_START' macro. For example, the above assignments to +`comment_caller' could instead be written + + + comment_caller = YY_START; + + Flex provides `YYSTATE' as an alias for `YY_START' (since that is +what's used by AT&T `lex'). + + For historical reasons, start conditions do not have their own +name-space within the generated scanner. The start condition names are +unmodified in the generated scanner and generated header. *Note +option-header::. *Note option-prefix::. + + Finally, here's an example of how to match C-style quoted strings +using exclusive start conditions, including expanded escape sequences +(but not including checking for a string that's too long): + + + %x str + + %% + char string_buf[MAX_STR_CONST]; + char *string_buf_ptr; + + + \" string_buf_ptr = string_buf; BEGIN(str); + + <str>\" { /* saw closing quote - all done */ + BEGIN(INITIAL); + *string_buf_ptr = '\0'; + /* return string constant token type and + * value to parser + */ + } + + <str>\n { + /* error - unterminated string constant */ + /* generate error message */ + } + + <str>\\[0-7]{1,3} { + /* octal escape sequence */ + int result; + + (void) sscanf( yytext + 1, "%o", &result ); + + if ( result > 0xff ) + /* error, constant is out-of-bounds */ + + *string_buf_ptr++ = result; + } + + <str>\\[0-9]+ { + /* generate error - bad escape sequence; something + * like '\48' or '\0777777' + */ + } + + <str>\\n *string_buf_ptr++ = '\n'; + <str>\\t *string_buf_ptr++ = '\t'; + <str>\\r *string_buf_ptr++ = '\r'; + <str>\\b *string_buf_ptr++ = '\b'; + <str>\\f *string_buf_ptr++ = '\f'; + + <str>\\(.|\n) *string_buf_ptr++ = yytext[1]; + + <str>[^\\\n\"]+ { + char *yptr = yytext; + + while ( *yptr ) + *string_buf_ptr++ = *yptr++; + } + + Often, such as in some of the examples above, you wind up writing a +whole bunch of rules all preceded by the same start condition(s). Flex +makes this a little easier and cleaner by introducing a notion of start +condition "scope". A start condition scope is begun with: + + + <SCs>{ + + where `SCs' is a list of one or more start conditions. Inside the +start condition scope, every rule automatically has the prefix `SCs>' +applied to it, until a `}' which matches the initial `{'. So, for +example, + + + <ESC>{ + "\\n" return '\n'; + "\\r" return '\r'; + "\\f" return '\f'; + "\\0" return '\0'; + } + + is equivalent to: + + + <ESC>"\\n" return '\n'; + <ESC>"\\r" return '\r'; + <ESC>"\\f" return '\f'; + <ESC>"\\0" return '\0'; + + Start condition scopes may be nested. + + The following routines are available for manipulating stacks of +start conditions: + + -- Function: void yy_push_state ( int `new_state' ) + pushes the current start condition onto the top of the start + condition stack and switches to `new_state' as though you had used + `BEGIN new_state' (recall that start condition names are also + integers). + + -- Function: void yy_pop_state () + pops the top of the stack and switches to it via `BEGIN'. + + -- Function: int yy_top_state () + returns the top of the stack without altering the stack's contents. + + The start condition stack grows dynamically and so has no built-in +size limitation. If memory is exhausted, program execution aborts. + + To use start condition stacks, your scanner must include a `%option +stack' directive (*note Scanner Options::). + + +File: flex.info, Node: Multiple Input Buffers, Next: EOF, Prev: Start Conditions, Up: Top + +11 Multiple Input Buffers +************************* + +Some scanners (such as those which support "include" files) require +reading from several input streams. As `flex' scanners do a large +amount of buffering, one cannot control where the next input will be +read from by simply writing a `YY_INPUT()' which is sensitive to the +scanning context. `YY_INPUT()' is only called when the scanner reaches +the end of its buffer, which may be a long time after scanning a +statement such as an `include' statement which requires switching the +input source. + + To negotiate these sorts of problems, `flex' provides a mechanism +for creating and switching between multiple input buffers. An input +buffer is created by using: + + -- Function: YY_BUFFER_STATE yy_create_buffer ( FILE *file, int size ) + + which takes a `FILE' pointer and a size and creates a buffer +associated with the given file and large enough to hold `size' +characters (when in doubt, use `YY_BUF_SIZE' for the size). It returns +a `YY_BUFFER_STATE' handle, which may then be passed to other routines +(see below). The `YY_BUFFER_STATE' type is a pointer to an opaque +`struct yy_buffer_state' structure, so you may safely initialize +`YY_BUFFER_STATE' variables to `((YY_BUFFER_STATE) 0)' if you wish, and +also refer to the opaque structure in order to correctly declare input +buffers in source files other than that of your scanner. Note that the +`FILE' pointer in the call to `yy_create_buffer' is only used as the +value of `yyin' seen by `YY_INPUT'. If you redefine `YY_INPUT()' so it +no longer uses `yyin', then you can safely pass a NULL `FILE' pointer to +`yy_create_buffer'. You select a particular buffer to scan from using: + + -- Function: void yy_switch_to_buffer ( YY_BUFFER_STATE new_buffer ) + + The above function switches the scanner's input buffer so subsequent +tokens will come from `new_buffer'. Note that `yy_switch_to_buffer()' +may be used by `yywrap()' to set things up for continued scanning, +instead of opening a new file and pointing `yyin' at it. If you are +looking for a stack of input buffers, then you want to use +`yypush_buffer_state()' instead of this function. Note also that +switching input sources via either `yy_switch_to_buffer()' or +`yywrap()' does _not_ change the start condition. + + -- Function: void yy_delete_buffer ( YY_BUFFER_STATE buffer ) + + is used to reclaim the storage associated with a buffer. (`buffer' +can be NULL, in which case the routine does nothing.) You can also +clear the current contents of a buffer using: + + -- Function: void yypush_buffer_state ( YY_BUFFER_STATE buffer ) + + This function pushes the new buffer state onto an internal stack. +The pushed state becomes the new current state. The stack is maintained +by flex and will grow as required. This function is intended to be used +instead of `yy_switch_to_buffer', when you want to change states, but +preserve the current state for later use. + + -- Function: void yypop_buffer_state ( ) + + This function removes the current state from the top of the stack, +and deletes it by calling `yy_delete_buffer'. The next state on the +stack, if any, becomes the new current state. + + -- Function: void yy_flush_buffer ( YY_BUFFER_STATE buffer ) + + This function discards the buffer's contents, so the next time the +scanner attempts to match a token from the buffer, it will first fill +the buffer anew using `YY_INPUT()'. + + -- Function: YY_BUFFER_STATE yy_new_buffer ( FILE *file, int size ) + + is an alias for `yy_create_buffer()', provided for compatibility +with the C++ use of `new' and `delete' for creating and destroying +dynamic objects. + + `YY_CURRENT_BUFFER' macro returns a `YY_BUFFER_STATE' handle to the +current buffer. It should not be used as an lvalue. + + Here are two examples of using these features for writing a scanner +which expands include files (the `<<EOF>>' feature is discussed below). + + This first example uses yypush_buffer_state and yypop_buffer_state. +Flex maintains the stack internally. + + + /* the "incl" state is used for picking up the name + * of an include file + */ + %x incl + %% + include BEGIN(incl); + + [a-z]+ ECHO; + [^a-z\n]*\n? ECHO; + + <incl>[ \t]* /* eat the whitespace */ + <incl>[^ \t\n]+ { /* got the include file name */ + yyin = fopen( yytext, "r" ); + + if ( ! yyin ) + error( ... ); + + yypush_buffer_state(yy_create_buffer( yyin, YY_BUF_SIZE )); + + BEGIN(INITIAL); + } + + <<EOF>> { + yypop_buffer_state(); + + if ( !YY_CURRENT_BUFFER ) + { + yyterminate(); + } + } + + The second example, below, does the same thing as the previous +example did, but manages its own input buffer stack manually (instead +of letting flex do it). + + + /* the "incl" state is used for picking up the name + * of an include file + */ + %x incl + + %{ + #define MAX_INCLUDE_DEPTH 10 + YY_BUFFER_STATE include_stack[MAX_INCLUDE_DEPTH]; + int include_stack_ptr = 0; + %} + + %% + include BEGIN(incl); + + [a-z]+ ECHO; + [^a-z\n]*\n? ECHO; + + <incl>[ \t]* /* eat the whitespace */ + <incl>[^ \t\n]+ { /* got the include file name */ + if ( include_stack_ptr >= MAX_INCLUDE_DEPTH ) + { + fprintf( stderr, "Includes nested too deeply" ); + exit( 1 ); + } + + include_stack[include_stack_ptr++] = + YY_CURRENT_BUFFER; + + yyin = fopen( yytext, "r" ); + + if ( ! yyin ) + error( ... ); + + yy_switch_to_buffer( + yy_create_buffer( yyin, YY_BUF_SIZE ) ); + + BEGIN(INITIAL); + } + + <<EOF>> { + if ( --include_stack_ptr 0 ) + { + yyterminate(); + } + + else + { + yy_delete_buffer( YY_CURRENT_BUFFER ); + yy_switch_to_buffer( + include_stack[include_stack_ptr] ); + } + } + + The following routines are available for setting up input buffers for +scanning in-memory strings instead of files. All of them create a new +input buffer for scanning the string, and return a corresponding +`YY_BUFFER_STATE' handle (which you should delete with +`yy_delete_buffer()' when done with it). They also switch to the new +buffer using `yy_switch_to_buffer()', so the next call to `yylex()' +will start scanning the string. + + -- Function: YY_BUFFER_STATE yy_scan_string ( const char *str ) + scans a NUL-terminated string. + + -- Function: YY_BUFFER_STATE yy_scan_bytes ( const char *bytes, int + len ) + scans `len' bytes (including possibly `NUL's) starting at location + `bytes'. + + Note that both of these functions create and scan a _copy_ of the +string or bytes. (This may be desirable, since `yylex()' modifies the +contents of the buffer it is scanning.) You can avoid the copy by +using: + + -- Function: YY_BUFFER_STATE yy_scan_buffer (char *base, yy_size_t + size) + which scans in place the buffer starting at `base', consisting of + `size' bytes, the last two bytes of which _must_ be + `YY_END_OF_BUFFER_CHAR' (ASCII NUL). These last two bytes are not + scanned; thus, scanning consists of `base[0]' through + `base[size-2]', inclusive. + + If you fail to set up `base' in this manner (i.e., forget the final +two `YY_END_OF_BUFFER_CHAR' bytes), then `yy_scan_buffer()' returns a +NULL pointer instead of creating a new input buffer. + + -- Data type: yy_size_t + is an integral type to which you can cast an integer expression + reflecting the size of the buffer. + + +File: flex.info, Node: EOF, Next: Misc Macros, Prev: Multiple Input Buffers, Up: Top + +12 End-of-File Rules +******************** + +The special rule `<<EOF>>' indicates actions which are to be taken when +an end-of-file is encountered and `yywrap()' returns non-zero (i.e., +indicates no further files to process). The action must finish by +doing one of the following things: + + * assigning `yyin' to a new input file (in previous versions of + `flex', after doing the assignment you had to call the special + action `YY_NEW_FILE'. This is no longer necessary.) + + * executing a `return' statement; + + * executing the special `yyterminate()' action. + + * or, switching to a new buffer using `yy_switch_to_buffer()' as + shown in the example above. + + <<EOF>> rules may not be used with other patterns; they may only be +qualified with a list of start conditions. If an unqualified <<EOF>> +rule is given, it applies to _all_ start conditions which do not +already have <<EOF>> actions. To specify an <<EOF>> rule for only the +initial start condition, use: + + + <INITIAL><<EOF>> + + These rules are useful for catching things like unclosed comments. +An example: + + + %x quote + %% + + ...other rules for dealing with quotes... + + <quote><<EOF>> { + error( "unterminated quote" ); + yyterminate(); + } + <<EOF>> { + if ( *++filelist ) + yyin = fopen( *filelist, "r" ); + else + yyterminate(); + } + + +File: flex.info, Node: Misc Macros, Next: User Values, Prev: EOF, Up: Top + +13 Miscellaneous Macros +*********************** + +The macro `YY_USER_ACTION' can be defined to provide an action which is +always executed prior to the matched rule's action. For example, it +could be #define'd to call a routine to convert yytext to lower-case. +When `YY_USER_ACTION' is invoked, the variable `yy_act' gives the +number of the matched rule (rules are numbered starting with 1). +Suppose you want to profile how often each of your rules is matched. +The following would do the trick: + + + #define YY_USER_ACTION ++ctr[yy_act] + + where `ctr' is an array to hold the counts for the different rules. +Note that the macro `YY_NUM_RULES' gives the total number of rules +(including the default rule), even if you use `-s)', so a correct +declaration for `ctr' is: + + + int ctr[YY_NUM_RULES]; + + The macro `YY_USER_INIT' may be defined to provide an action which +is always executed before the first scan (and before the scanner's +internal initializations are done). For example, it could be used to +call a routine to read in a data table or open a logging file. + + The macro `yy_set_interactive(is_interactive)' can be used to +control whether the current buffer is considered "interactive". An +interactive buffer is processed more slowly, but must be used when the +scanner's input source is indeed interactive to avoid problems due to +waiting to fill buffers (see the discussion of the `-I' flag in *Note +Scanner Options::). A non-zero value in the macro invocation marks the +buffer as interactive, a zero value as non-interactive. Note that use +of this macro overrides `%option always-interactive' or `%option +never-interactive' (*note Scanner Options::). `yy_set_interactive()' +must be invoked prior to beginning to scan the buffer that is (or is +not) to be considered interactive. + + The macro `yy_set_bol(at_bol)' can be used to control whether the +current buffer's scanning context for the next token match is done as +though at the beginning of a line. A non-zero macro argument makes +rules anchored with `^' active, while a zero argument makes `^' rules +inactive. + + The macro `YY_AT_BOL()' returns true if the next token scanned from +the current buffer will have `^' rules active, false otherwise. + + In the generated scanner, the actions are all gathered in one large +switch statement and separated using `YY_BREAK', which may be +redefined. By default, it is simply a `break', to separate each rule's +action from the following rule's. Redefining `YY_BREAK' allows, for +example, C++ users to #define YY_BREAK to do nothing (while being very +careful that every rule ends with a `break' or a `return'!) to avoid +suffering from unreachable statement warnings where because a rule's +action ends with `return', the `YY_BREAK' is inaccessible. + + +File: flex.info, Node: User Values, Next: Yacc, Prev: Misc Macros, Up: Top + +14 Values Available To the User +******************************* + +This chapter summarizes the various values available to the user in the +rule actions. + +`char *yytext' + holds the text of the current token. It may be modified but not + lengthened (you cannot append characters to the end). + + If the special directive `%array' appears in the first section of + the scanner description, then `yytext' is instead declared `char + yytext[YYLMAX]', where `YYLMAX' is a macro definition that you can + redefine in the first section if you don't like the default value + (generally 8KB). Using `%array' results in somewhat slower + scanners, but the value of `yytext' becomes immune to calls to + `unput()', which potentially destroy its value when `yytext' is a + character pointer. The opposite of `%array' is `%pointer', which + is the default. + + You cannot use `%array' when generating C++ scanner classes (the + `-+' flag). + +`int yyleng' + holds the length of the current token. + +`FILE *yyin' + is the file which by default `flex' reads from. It may be + redefined but doing so only makes sense before scanning begins or + after an EOF has been encountered. Changing it in the midst of + scanning will have unexpected results since `flex' buffers its + input; use `yyrestart()' instead. Once scanning terminates + because an end-of-file has been seen, you can assign `yyin' at the + new input file and then call the scanner again to continue + scanning. + +`void yyrestart( FILE *new_file )' + may be called to point `yyin' at the new input file. The + switch-over to the new file is immediate (any previously + buffered-up input is lost). Note that calling `yyrestart()' with + `yyin' as an argument thus throws away the current input buffer + and continues scanning the same input file. + +`FILE *yyout' + is the file to which `ECHO' actions are done. It can be reassigned + by the user. + +`YY_CURRENT_BUFFER' + returns a `YY_BUFFER_STATE' handle to the current buffer. + +`YY_START' + returns an integer value corresponding to the current start + condition. You can subsequently use this value with `BEGIN' to + return to that start condition. + + +File: flex.info, Node: Yacc, Next: Scanner Options, Prev: User Values, Up: Top + +15 Interfacing with Yacc +************************ + +One of the main uses of `flex' is as a companion to the `yacc' +parser-generator. `yacc' parsers expect to call a routine named +`yylex()' to find the next input token. The routine is supposed to +return the type of the next token as well as putting any associated +value in the global `yylval'. To use `flex' with `yacc', one specifies +the `-d' option to `yacc' to instruct it to generate the file `y.tab.h' +containing definitions of all the `%tokens' appearing in the `yacc' +input. This file is then included in the `flex' scanner. For example, +if one of the tokens is `TOK_NUMBER', part of the scanner might look +like: + + + %{ + #include "y.tab.h" + %} + + %% + + [0-9]+ yylval = atoi( yytext ); return TOK_NUMBER; + + +File: flex.info, Node: Scanner Options, Next: Performance, Prev: Yacc, Up: Top + +16 Scanner Options +****************** + +The various `flex' options are categorized by function in the following +menu. If you want to lookup a particular option by name, *Note Index of +Scanner Options::. + +* Menu: + +* Options for Specifying Filenames:: +* Options Affecting Scanner Behavior:: +* Code-Level And API Options:: +* Options for Scanner Speed and Size:: +* Debugging Options:: +* Miscellaneous Options:: + + Even though there are many scanner options, a typical scanner might +only specify the following options: + + + %option 8bit reentrant bison-bridge + %option warn nodefault + %option yylineno + %option outfile="scanner.c" header-file="scanner.h" + + The first line specifies the general type of scanner we want. The +second line specifies that we are being careful. The third line asks +flex to track line numbers. The last line tells flex what to name the +files. (The options can be specified in any order. We just divided +them.) + + `flex' also provides a mechanism for controlling options within the +scanner specification itself, rather than from the flex command-line. +This is done by including `%option' directives in the first section of +the scanner specification. You can specify multiple options with a +single `%option' directive, and multiple directives in the first +section of your flex input file. + + Most options are given simply as names, optionally preceded by the +word `no' (with no intervening whitespace) to negate their meaning. +The names are the same as their long-option equivalents (but without the +leading `--' ). + + `flex' scans your rule actions to determine whether you use the +`REJECT' or `yymore()' features. The `REJECT' and `yymore' options are +available to override its decision as to whether you use the options, +either by setting them (e.g., `%option reject)' to indicate the feature +is indeed used, or unsetting them to indicate it actually is not used +(e.g., `%option noyymore)'. + + A number of options are available for lint purists who want to +suppress the appearance of unneeded routines in the generated scanner. +Each of the following, if unset (e.g., `%option nounput'), results in +the corresponding routine not appearing in the generated scanner: + + + input, unput + yy_push_state, yy_pop_state, yy_top_state + yy_scan_buffer, yy_scan_bytes, yy_scan_string + + yyget_extra, yyset_extra, yyget_leng, yyget_text, + yyget_lineno, yyset_lineno, yyget_in, yyset_in, + yyget_out, yyset_out, yyget_lval, yyset_lval, + yyget_lloc, yyset_lloc, yyget_debug, yyset_debug + + (though `yy_push_state()' and friends won't appear anyway unless you +use `%option stack)'. + + +File: flex.info, Node: Options for Specifying Filenames, Next: Options Affecting Scanner Behavior, Prev: Scanner Options, Up: Scanner Options + +16.1 Options for Specifying Filenames +===================================== + +`--header-file=FILE, `%option header-file="FILE"'' + instructs flex to write a C header to `FILE'. This file contains + function prototypes, extern variables, and types used by the + scanner. Only the external API is exported by the header file. + Many macros that are usable from within scanner actions are not + exported to the header file. This is due to namespace problems and + the goal of a clean external API. + + While in the header, the macro `yyIN_HEADER' is defined, where `yy' + is substituted with the appropriate prefix. + + The `--header-file' option is not compatible with the `--c++' + option, since the C++ scanner provides its own header in + `yyFlexLexer.h'. + +`-oFILE, --outfile=FILE, `%option outfile="FILE"'' + directs flex to write the scanner to the file `FILE' instead of + `lex.yy.c'. If you combine `--outfile' with the `--stdout' option, + then the scanner is written to `stdout' but its `#line' directives + (see the `-l' option above) refer to the file `FILE'. + +`-t, --stdout, `%option stdout'' + instructs `flex' to write the scanner it generates to standard + output instead of `lex.yy.c'. + +`-SFILE, --skel=FILE' + overrides the default skeleton file from which `flex' constructs + its scanners. You'll never need this option unless you are doing + `flex' maintenance or development. + +`--tables-file=FILE' + Write serialized scanner dfa tables to FILE. The generated scanner + will not contain the tables, and requires them to be loaded at + runtime. *Note serialization::. + +`--tables-verify' + This option is for flex development. We document it here in case + you stumble upon it by accident or in case you suspect some + inconsistency in the serialized tables. Flex will serialize the + scanner dfa tables but will also generate the in-code tables as it + normally does. At runtime, the scanner will verify that the + serialized tables match the in-code tables, instead of loading + them. + + + +File: flex.info, Node: Options Affecting Scanner Behavior, Next: Code-Level And API Options, Prev: Options for Specifying Filenames, Up: Scanner Options + +16.2 Options Affecting Scanner Behavior +======================================= + +`-i, --case-insensitive, `%option case-insensitive'' + instructs `flex' to generate a "case-insensitive" scanner. The + case of letters given in the `flex' input patterns will be ignored, + and tokens in the input will be matched regardless of case. The + matched text given in `yytext' will have the preserved case (i.e., + it will not be folded). For tricky behavior, see *Note case and + character ranges::. + +`-l, --lex-compat, `%option lex-compat'' + turns on maximum compatibility with the original AT&T `lex' + implementation. Note that this does not mean _full_ compatibility. + Use of this option costs a considerable amount of performance, and + it cannot be used with the `--c++', `--full', `--fast', `-Cf', or + `-CF' options. For details on the compatibilities it provides, see + *Note Lex and Posix::. This option also results in the name + `YY_FLEX_LEX_COMPAT' being `#define''d in the generated scanner. + +`-B, --batch, `%option batch'' + instructs `flex' to generate a "batch" scanner, the opposite of + _interactive_ scanners generated by `--interactive' (see below). + In general, you use `-B' when you are _certain_ that your scanner + will never be used interactively, and you want to squeeze a + _little_ more performance out of it. If your goal is instead to + squeeze out a _lot_ more performance, you should be using the + `-Cf' or `-CF' options, which turn on `--batch' automatically + anyway. + +`-I, --interactive, `%option interactive'' + instructs `flex' to generate an interactive scanner. An + interactive scanner is one that only looks ahead to decide what + token has been matched if it absolutely must. It turns out that + always looking one extra character ahead, even if the scanner has + already seen enough text to disambiguate the current token, is a + bit faster than only looking ahead when necessary. But scanners + that always look ahead give dreadful interactive performance; for + example, when a user types a newline, it is not recognized as a + newline token until they enter _another_ token, which often means + typing in another whole line. + + `flex' scanners default to `interactive' unless you use the `-Cf' + or `-CF' table-compression options (*note Performance::). That's + because if you're looking for high-performance you should be using + one of these options, so if you didn't, `flex' assumes you'd + rather trade off a bit of run-time performance for intuitive + interactive behavior. Note also that you _cannot_ use + `--interactive' in conjunction with `-Cf' or `-CF'. Thus, this + option is not really needed; it is on by default for all those + cases in which it is allowed. + + You can force a scanner to _not_ be interactive by using `--batch' + +`-7, --7bit, `%option 7bit'' + instructs `flex' to generate a 7-bit scanner, i.e., one which can + only recognize 7-bit characters in its input. The advantage of + using `--7bit' is that the scanner's tables can be up to half the + size of those generated using the `--8bit'. The disadvantage is + that such scanners often hang or crash if their input contains an + 8-bit character. + + Note, however, that unless you generate your scanner using the + `-Cf' or `-CF' table compression options, use of `--7bit' will + save only a small amount of table space, and make your scanner + considerably less portable. `Flex''s default behavior is to + generate an 8-bit scanner unless you use the `-Cf' or `-CF', in + which case `flex' defaults to generating 7-bit scanners unless + your site was always configured to generate 8-bit scanners (as will + often be the case with non-USA sites). You can tell whether flex + generated a 7-bit or an 8-bit scanner by inspecting the flag + summary in the `--verbose' output as described above. + + Note that if you use `-Cfe' or `-CFe' `flex' still defaults to + generating an 8-bit scanner, since usually with these compression + options full 8-bit tables are not much more expensive than 7-bit + tables. + +`-8, --8bit, `%option 8bit'' + instructs `flex' to generate an 8-bit scanner, i.e., one which can + recognize 8-bit characters. This flag is only needed for scanners + generated using `-Cf' or `-CF', as otherwise flex defaults to + generating an 8-bit scanner anyway. + + See the discussion of `--7bit' above for `flex''s default behavior + and the tradeoffs between 7-bit and 8-bit scanners. + +`--default, `%option default'' + generate the default rule. + +`--always-interactive, `%option always-interactive'' + instructs flex to generate a scanner which always considers its + input _interactive_. Normally, on each new input file the scanner + calls `isatty()' in an attempt to determine whether the scanner's + input source is interactive and thus should be read a character at + a time. When this option is used, however, then no such call is + made. + +`--never-interactive, `--never-interactive'' + instructs flex to generate a scanner which never considers its + input interactive. This is the opposite of `always-interactive'. + +`-X, --posix, `%option posix'' + turns on maximum compatibility with the POSIX 1003.2-1992 + definition of `lex'. Since `flex' was originally designed to + implement the POSIX definition of `lex' this generally involves + very few changes in behavior. At the current writing the known + differences between `flex' and the POSIX standard are: + + * In POSIX and AT&T `lex', the repeat operator, `{}', has lower + precedence than concatenation (thus `ab{3}' yields `ababab'). + Most POSIX utilities use an Extended Regular Expression (ERE) + precedence that has the precedence of the repeat operator + higher than concatenation (which causes `ab{3}' to yield + `abbb'). By default, `flex' places the precedence of the + repeat operator higher than concatenation which matches the + ERE processing of other POSIX utilities. When either + `--posix' or `-l' are specified, `flex' will use the + traditional AT&T and POSIX-compliant precedence for the + repeat operator where concatenation has higher precedence + than the repeat operator. + +`--stack, `%option stack'' + enables the use of start condition stacks (*note Start + Conditions::). + +`--stdinit, `%option stdinit'' + if set (i.e., %option stdinit) initializes `yyin' and `yyout' to + `stdin' and `stdout', instead of the default of `NULL'. Some + existing `lex' programs depend on this behavior, even though it is + not compliant with ANSI C, which does not require `stdin' and + `stdout' to be compile-time constant. In a reentrant scanner, + however, this is not a problem since initialization is performed + in `yylex_init' at runtime. + +`--yylineno, `%option yylineno'' + directs `flex' to generate a scanner that maintains the number of + the current line read from its input in the global variable + `yylineno'. This option is implied by `%option lex-compat'. In a + reentrant C scanner, the macro `yylineno' is accessible regardless + of the value of `%option yylineno', however, its value is not + modified by `flex' unless `%option yylineno' is enabled. + +`--yywrap, `%option yywrap'' + if unset (i.e., `--noyywrap)', makes the scanner not call + `yywrap()' upon an end-of-file, but simply assume that there are no + more files to scan (until the user points `yyin' at a new file and + calls `yylex()' again). + + + +File: flex.info, Node: Code-Level And API Options, Next: Options for Scanner Speed and Size, Prev: Options Affecting Scanner Behavior, Up: Scanner Options + +16.3 Code-Level And API Options +=============================== + +`--ansi-definitions, `%option ansi-definitions'' + instruct flex to generate ANSI C99 definitions for functions. + This option is enabled by default. If `%option + noansi-definitions' is specified, then the obsolete style is + generated. + +`--ansi-prototypes, `%option ansi-prototypes'' + instructs flex to generate ANSI C99 prototypes for functions. + This option is enabled by default. If `noansi-prototypes' is + specified, then prototypes will have empty parameter lists. + +`--bison-bridge, `%option bison-bridge'' + instructs flex to generate a C scanner that is meant to be called + by a `GNU bison' parser. The scanner has minor API changes for + `bison' compatibility. In particular, the declaration of `yylex' + is modified to take an additional parameter, `yylval'. *Note + Bison Bridge::. + +`--bison-locations, `%option bison-locations'' + instruct flex that `GNU bison' `%locations' are being used. This + means `yylex' will be passed an additional parameter, `yylloc'. + This option implies `%option bison-bridge'. *Note Bison Bridge::. + +`-L, --noline, `%option noline'' + instructs `flex' not to generate `#line' directives. Without this + option, `flex' peppers the generated scanner with `#line' + directives so error messages in the actions will be correctly + located with respect to either the original `flex' input file (if + the errors are due to code in the input file), or `lex.yy.c' (if + the errors are `flex''s fault - you should report these sorts of + errors to the email address given in *Note Reporting Bugs::). + +`-R, --reentrant, `%option reentrant'' + instructs flex to generate a reentrant C scanner. The generated + scanner may safely be used in a multi-threaded environment. The + API for a reentrant scanner is different than for a non-reentrant + scanner *note Reentrant::). Because of the API difference between + reentrant and non-reentrant `flex' scanners, non-reentrant flex + code must be modified before it is suitable for use with this + option. This option is not compatible with the `--c++' option. + + The option `--reentrant' does not affect the performance of the + scanner. + +`-+, --c++, `%option c++'' + specifies that you want flex to generate a C++ scanner class. + *Note Cxx::, for details. + +`--array, `%option array'' + specifies that you want yytext to be an array instead of a char* + +`--pointer, `%option pointer'' + specify that `yytext' should be a `char *', not an array. This + default is `char *'. + +`-PPREFIX, --prefix=PREFIX, `%option prefix="PREFIX"'' + changes the default `yy' prefix used by `flex' for all + globally-visible variable and function names to instead be + `PREFIX'. For example, `--prefix=foo' changes the name of + `yytext' to `footext'. It also changes the name of the default + output file from `lex.yy.c' to `lex.foo.c'. Here is a partial + list of the names affected: + + + yy_create_buffer + yy_delete_buffer + yy_flex_debug + yy_init_buffer + yy_flush_buffer + yy_load_buffer_state + yy_switch_to_buffer + yyin + yyleng + yylex + yylineno + yyout + yyrestart + yytext + yywrap + yyalloc + yyrealloc + yyfree + + (If you are using a C++ scanner, then only `yywrap' and + `yyFlexLexer' are affected.) Within your scanner itself, you can + still refer to the global variables and functions using either + version of their name; but externally, they have the modified name. + + This option lets you easily link together multiple `flex' programs + into the same executable. Note, though, that using this option + also renames `yywrap()', so you now _must_ either provide your own + (appropriately-named) version of the routine for your scanner, or + use `%option noyywrap', as linking with `-lfl' no longer provides + one for you by default. + +`--main, `%option main'' + directs flex to provide a default `main()' program for the + scanner, which simply calls `yylex()'. This option implies + `noyywrap' (see below). + +`--nounistd, `%option nounistd'' + suppresses inclusion of the non-ANSI header file `unistd.h'. This + option is meant to target environments in which `unistd.h' does + not exist. Be aware that certain options may cause flex to + generate code that relies on functions normally found in + `unistd.h', (e.g. `isatty()', `read()'.) If you wish to use these + functions, you will have to inform your compiler where to find + them. *Note option-always-interactive::. *Note option-read::. + +`--yyclass=NAME, `%option yyclass="NAME"'' + only applies when generating a C++ scanner (the `--c++' option). + It informs `flex' that you have derived `NAME' as a subclass of + `yyFlexLexer', so `flex' will place your actions in the member + function `foo::yylex()' instead of `yyFlexLexer::yylex()'. It + also generates a `yyFlexLexer::yylex()' member function that emits + a run-time error (by invoking `yyFlexLexer::LexerError())' if + called. *Note Cxx::. + + + +File: flex.info, Node: Options for Scanner Speed and Size, Next: Debugging Options, Prev: Code-Level And API Options, Up: Scanner Options + +16.4 Options for Scanner Speed and Size +======================================= + +`-C[aefFmr]' + controls the degree of table compression and, more generally, + trade-offs between small scanners and fast scanners. + + `-C' + A lone `-C' specifies that the scanner tables should be + compressed but neither equivalence classes nor + meta-equivalence classes should be used. + + `-Ca, --align, `%option align'' + ("align") instructs flex to trade off larger tables in the + generated scanner for faster performance because the elements + of the tables are better aligned for memory access and + computation. On some RISC architectures, fetching and + manipulating longwords is more efficient than with + smaller-sized units such as shortwords. This option can + quadruple the size of the tables used by your scanner. + + `-Ce, --ecs, `%option ecs'' + directs `flex' to construct "equivalence classes", i.e., sets + of characters which have identical lexical properties (for + example, if the only appearance of digits in the `flex' input + is in the character class "[0-9]" then the digits '0', '1', + ..., '9' will all be put in the same equivalence class). + Equivalence classes usually give dramatic reductions in the + final table/object file sizes (typically a factor of 2-5) and + are pretty cheap performance-wise (one array look-up per + character scanned). + + `-Cf' + specifies that the "full" scanner tables should be generated - + `flex' should not compress the tables by taking advantages of + similar transition functions for different states. + + `-CF' + specifies that the alternate fast scanner representation + (described above under the `--fast' flag) should be used. + This option cannot be used with `--c++'. + + `-Cm, --meta-ecs, `%option meta-ecs'' + directs `flex' to construct "meta-equivalence classes", which + are sets of equivalence classes (or characters, if equivalence + classes are not being used) that are commonly used together. + Meta-equivalence classes are often a big win when using + compressed tables, but they have a moderate performance + impact (one or two `if' tests and one array look-up per + character scanned). + + `-Cr, --read, `%option read'' + causes the generated scanner to _bypass_ use of the standard + I/O library (`stdio') for input. Instead of calling + `fread()' or `getc()', the scanner will use the `read()' + system call, resulting in a performance gain which varies + from system to system, but in general is probably negligible + unless you are also using `-Cf' or `-CF'. Using `-Cr' can + cause strange behavior if, for example, you read from `yyin' + using `stdio' prior to calling the scanner (because the + scanner will miss whatever text your previous reads left in + the `stdio' input buffer). `-Cr' has no effect if you define + `YY_INPUT()' (*note Generated Scanner::). + + The options `-Cf' or `-CF' and `-Cm' do not make sense together - + there is no opportunity for meta-equivalence classes if the table + is not being compressed. Otherwise the options may be freely + mixed, and are cumulative. + + The default setting is `-Cem', which specifies that `flex' should + generate equivalence classes and meta-equivalence classes. This + setting provides the highest degree of table compression. You can + trade off faster-executing scanners at the cost of larger tables + with the following generally being true: + + + slowest & smallest + -Cem + -Cm + -Ce + -C + -C{f,F}e + -C{f,F} + -C{f,F}a + fastest & largest + + Note that scanners with the smallest tables are usually generated + and compiled the quickest, so during development you will usually + want to use the default, maximal compression. + + `-Cfe' is often a good compromise between speed and size for + production scanners. + +`-f, --full, `%option full'' + specifies "fast scanner". No table compression is done and + `stdio' is bypassed. The result is large but fast. This option + is equivalent to `--Cfr' + +`-F, --fast, `%option fast'' + specifies that the _fast_ scanner table representation should be + used (and `stdio' bypassed). This representation is about as fast + as the full table representation `--full', and for some sets of + patterns will be considerably smaller (and for others, larger). In + general, if the pattern set contains both _keywords_ and a + catch-all, _identifier_ rule, such as in the set: + + + "case" return TOK_CASE; + "switch" return TOK_SWITCH; + ... + "default" return TOK_DEFAULT; + [a-z]+ return TOK_ID; + + then you're better off using the full table representation. If + only the _identifier_ rule is present and you then use a hash + table or some such to detect the keywords, you're better off using + `--fast'. + + This option is equivalent to `-CFr'. It cannot be used with + `--c++'. + + + +File: flex.info, Node: Debugging Options, Next: Miscellaneous Options, Prev: Options for Scanner Speed and Size, Up: Scanner Options + +16.5 Debugging Options +====================== + +`-b, --backup, `%option backup'' + Generate backing-up information to `lex.backup'. This is a list of + scanner states which require backing up and the input characters on + which they do so. By adding rules one can remove backing-up + states. If _all_ backing-up states are eliminated and `-Cf' or + `-CF' is used, the generated scanner will run faster (see the + `--perf-report' flag). Only users who wish to squeeze every last + cycle out of their scanners need worry about this option. (*note + Performance::). + +`-d, --debug, `%option debug'' + makes the generated scanner run in "debug" mode. Whenever a + pattern is recognized and the global variable `yy_flex_debug' is + non-zero (which is the default), the scanner will write to + `stderr' a line of the form: + + + -accepting rule at line 53 ("the matched text") + + The line number refers to the location of the rule in the file + defining the scanner (i.e., the file that was fed to flex). + Messages are also generated when the scanner backs up, accepts the + default rule, reaches the end of its input buffer (or encounters a + NUL; at this point, the two look the same as far as the scanner's + concerned), or reaches an end-of-file. + +`-p, --perf-report, `%option perf-report'' + generates a performance report to `stderr'. The report consists of + comments regarding features of the `flex' input file which will + cause a serious loss of performance in the resulting scanner. If + you give the flag twice, you will also get comments regarding + features that lead to minor performance losses. + + Note that the use of `REJECT', and variable trailing context + (*note Limitations::) entails a substantial performance penalty; + use of `yymore()', the `^' operator, and the `--interactive' flag + entail minor performance penalties. + +`-s, --nodefault, `%option nodefault'' + causes the _default rule_ (that unmatched scanner input is echoed + to `stdout)' to be suppressed. If the scanner encounters input + that does not match any of its rules, it aborts with an error. + This option is useful for finding holes in a scanner's rule set. + +`-T, --trace, `%option trace'' + makes `flex' run in "trace" mode. It will generate a lot of + messages to `stderr' concerning the form of the input and the + resultant non-deterministic and deterministic finite automata. + This option is mostly for use in maintaining `flex'. + +`-w, --nowarn, `%option nowarn'' + suppresses warning messages. + +`-v, --verbose, `%option verbose'' + specifies that `flex' should write to `stderr' a summary of + statistics regarding the scanner it generates. Most of the + statistics are meaningless to the casual `flex' user, but the + first line identifies the version of `flex' (same as reported by + `--version'), and the next line the flags used when generating the + scanner, including those that are on by default. + +`--warn, `%option warn'' + warn about certain things. In particular, if the default rule can + be matched but no default rule has been given, the flex will warn + you. We recommend using this option always. + + + +File: flex.info, Node: Miscellaneous Options, Prev: Debugging Options, Up: Scanner Options + +16.6 Miscellaneous Options +========================== + +`-c' + A do-nothing option included for POSIX compliance. + +`-h, -?, --help' + generates a "help" summary of `flex''s options to `stdout' and + then exits. + +`-n' + Another do-nothing option included for POSIX compliance. + +`-V, --version' + prints the version number to `stdout' and exits. + + + +File: flex.info, Node: Performance, Next: Cxx, Prev: Scanner Options, Up: Top + +17 Performance Considerations +***************************** + +The main design goal of `flex' is that it generate high-performance +scanners. It has been optimized for dealing well with large sets of +rules. Aside from the effects on scanner speed of the table compression +`-C' options outlined above, there are a number of options/actions +which degrade performance. These are, from most expensive to least: + + + REJECT + arbitrary trailing context + + pattern sets that require backing up + %option yylineno + %array + + %option interactive + %option always-interactive + + @samp{^} beginning-of-line operator + yymore() + + with the first two all being quite expensive and the last two being +quite cheap. Note also that `unput()' is implemented as a routine call +that potentially does quite a bit of work, while `yyless()' is a +quite-cheap macro. So if you are just putting back some excess text you +scanned, use `yyless()'. + + `REJECT' should be avoided at all costs when performance is +important. It is a particularly expensive option. + + There is one case when `%option yylineno' can be expensive. That is +when your patterns match long tokens that could _possibly_ contain a +newline character. There is no performance penalty for rules that can +not possibly match newlines, since flex does not need to check them for +newlines. In general, you should avoid rules such as `[^f]+', which +match very long tokens, including newlines, and may possibly match your +entire file! A better approach is to separate `[^f]+' into two rules: + + + %option yylineno + %% + [^f\n]+ + \n+ + + The above scanner does not incur a performance penalty. + + Getting rid of backing up is messy and often may be an enormous +amount of work for a complicated scanner. In principal, one begins by +using the `-b' flag to generate a `lex.backup' file. For example, on +the input: + + + %% + foo return TOK_KEYWORD; + foobar return TOK_KEYWORD; + + the file looks like: + + + State #6 is non-accepting - + associated rule line numbers: + 2 3 + out-transitions: [ o ] + jam-transitions: EOF [ \001-n p-\177 ] + + State #8 is non-accepting - + associated rule line numbers: + 3 + out-transitions: [ a ] + jam-transitions: EOF [ \001-` b-\177 ] + + State #9 is non-accepting - + associated rule line numbers: + 3 + out-transitions: [ r ] + jam-transitions: EOF [ \001-q s-\177 ] + + Compressed tables always back up. + + The first few lines tell us that there's a scanner state in which it +can make a transition on an 'o' but not on any other character, and +that in that state the currently scanned text does not match any rule. +The state occurs when trying to match the rules found at lines 2 and 3 +in the input file. If the scanner is in that state and then reads +something other than an 'o', it will have to back up to find a rule +which is matched. With a bit of headscratching one can see that this +must be the state it's in when it has seen `fo'. When this has +happened, if anything other than another `o' is seen, the scanner will +have to back up to simply match the `f' (by the default rule). + + The comment regarding State #8 indicates there's a problem when +`foob' has been scanned. Indeed, on any character other than an `a', +the scanner will have to back up to accept "foo". Similarly, the +comment for State #9 concerns when `fooba' has been scanned and an `r' +does not follow. + + The final comment reminds us that there's no point going to all the +trouble of removing backing up from the rules unless we're using `-Cf' +or `-CF', since there's no performance gain doing so with compressed +scanners. + + The way to remove the backing up is to add "error" rules: + + + %% + foo return TOK_KEYWORD; + foobar return TOK_KEYWORD; + + fooba | + foob | + fo { + /* false alarm, not really a keyword */ + return TOK_ID; + } + + Eliminating backing up among a list of keywords can also be done +using a "catch-all" rule: + + + %% + foo return TOK_KEYWORD; + foobar return TOK_KEYWORD; + + [a-z]+ return TOK_ID; + + This is usually the best solution when appropriate. + + Backing up messages tend to cascade. With a complicated set of rules +it's not uncommon to get hundreds of messages. If one can decipher +them, though, it often only takes a dozen or so rules to eliminate the +backing up (though it's easy to make a mistake and have an error rule +accidentally match a valid token. A possible future `flex' feature +will be to automatically add rules to eliminate backing up). + + It's important to keep in mind that you gain the benefits of +eliminating backing up only if you eliminate _every_ instance of +backing up. Leaving just one means you gain nothing. + + _Variable_ trailing context (where both the leading and trailing +parts do not have a fixed length) entails almost the same performance +loss as `REJECT' (i.e., substantial). So when possible a rule like: + + + %% + mouse|rat/(cat|dog) run(); + + is better written: + + + %% + mouse/cat|dog run(); + rat/cat|dog run(); + + or as + + + %% + mouse|rat/cat run(); + mouse|rat/dog run(); + + Note that here the special '|' action does _not_ provide any +savings, and can even make things worse (*note Limitations::). + + Another area where the user can increase a scanner's performance (and +one that's easier to implement) arises from the fact that the longer the +tokens matched, the faster the scanner will run. This is because with +long tokens the processing of most input characters takes place in the +(short) inner scanning loop, and does not often have to go through the +additional work of setting up the scanning environment (e.g., `yytext') +for the action. Recall the scanner for C comments: + + + %x comment + %% + int line_num = 1; + + "/*" BEGIN(comment); + + <comment>[^*\n]* + <comment>"*"+[^*/\n]* + <comment>\n ++line_num; + <comment>"*"+"/" BEGIN(INITIAL); + + This could be sped up by writing it as: + + + %x comment + %% + int line_num = 1; + + "/*" BEGIN(comment); + + <comment>[^*\n]* + <comment>[^*\n]*\n ++line_num; + <comment>"*"+[^*/\n]* + <comment>"*"+[^*/\n]*\n ++line_num; + <comment>"*"+"/" BEGIN(INITIAL); + + Now instead of each newline requiring the processing of another +action, recognizing the newlines is distributed over the other rules to +keep the matched text as long as possible. Note that _adding_ rules +does _not_ slow down the scanner! The speed of the scanner is +independent of the number of rules or (modulo the considerations given +at the beginning of this section) how complicated the rules are with +regard to operators such as `*' and `|'. + + A final example in speeding up a scanner: suppose you want to scan +through a file containing identifiers and keywords, one per line and +with no other extraneous characters, and recognize all the keywords. A +natural first approach is: + + + %% + asm | + auto | + break | + ... etc ... + volatile | + while /* it's a keyword */ + + .|\n /* it's not a keyword */ + + To eliminate the back-tracking, introduce a catch-all rule: + + + %% + asm | + auto | + break | + ... etc ... + volatile | + while /* it's a keyword */ + + [a-z]+ | + .|\n /* it's not a keyword */ + + Now, if it's guaranteed that there's exactly one word per line, then +we can reduce the total number of matches by a half by merging in the +recognition of newlines with that of the other tokens: + + + %% + asm\n | + auto\n | + break\n | + ... etc ... + volatile\n | + while\n /* it's a keyword */ + + [a-z]+\n | + .|\n /* it's not a keyword */ + + One has to be careful here, as we have now reintroduced backing up +into the scanner. In particular, while _we_ know that there will never +be any characters in the input stream other than letters or newlines, +`flex' can't figure this out, and it will plan for possibly needing to +back up when it has scanned a token like `auto' and then the next +character is something other than a newline or a letter. Previously it +would then just match the `auto' rule and be done, but now it has no +`auto' rule, only a `auto\n' rule. To eliminate the possibility of +backing up, we could either duplicate all rules but without final +newlines, or, since we never expect to encounter such an input and +therefore don't how it's classified, we can introduce one more +catch-all rule, this one which doesn't include a newline: + + + %% + asm\n | + auto\n | + break\n | + ... etc ... + volatile\n | + while\n /* it's a keyword */ + + [a-z]+\n | + [a-z]+ | + .|\n /* it's not a keyword */ + + Compiled with `-Cf', this is about as fast as one can get a `flex' +scanner to go for this particular problem. + + A final note: `flex' is slow when matching `NUL's, particularly when +a token contains multiple `NUL's. It's best to write rules which match +_short_ amounts of text if it's anticipated that the text will often +include `NUL's. + + Another final note regarding performance: as mentioned in *Note +Matching::, dynamically resizing `yytext' to accommodate huge tokens is +a slow process because it presently requires that the (huge) token be +rescanned from the beginning. Thus if performance is vital, you should +attempt to match "large" quantities of text but not "huge" quantities, +where the cutoff between the two is at about 8K characters per token. + + +File: flex.info, Node: Cxx, Next: Reentrant, Prev: Performance, Up: Top + +18 Generating C++ Scanners +************************** + +*IMPORTANT*: the present form of the scanning class is _experimental_ +and may change considerably between major releases. + + `flex' provides two different ways to generate scanners for use with +C++. The first way is to simply compile a scanner generated by `flex' +using a C++ compiler instead of a C compiler. You should not encounter +any compilation errors (*note Reporting Bugs::). You can then use C++ +code in your rule actions instead of C code. Note that the default +input source for your scanner remains `yyin', and default echoing is +still done to `yyout'. Both of these remain `FILE *' variables and not +C++ _streams_. + + You can also use `flex' to generate a C++ scanner class, using the +`-+' option (or, equivalently, `%option c++)', which is automatically +specified if the name of the `flex' executable ends in a '+', such as +`flex++'. When using this option, `flex' defaults to generating the +scanner to the file `lex.yy.cc' instead of `lex.yy.c'. The generated +scanner includes the header file `FlexLexer.h', which defines the +interface to two C++ classes. + + The first class, `FlexLexer', provides an abstract base class +defining the general scanner class interface. It provides the +following member functions: + +`const char* YYText()' + returns the text of the most recently matched token, the + equivalent of `yytext'. + +`int YYLeng()' + returns the length of the most recently matched token, the + equivalent of `yyleng'. + +`int lineno() const' + returns the current input line number (see `%option yylineno)', or + `1' if `%option yylineno' was not used. + +`void set_debug( int flag )' + sets the debugging flag for the scanner, equivalent to assigning to + `yy_flex_debug' (*note Scanner Options::). Note that you must + build the scanner using `%option debug' to include debugging + information in it. + +`int debug() const' + returns the current setting of the debugging flag. + + Also provided are member functions equivalent to +`yy_switch_to_buffer()', `yy_create_buffer()' (though the first +argument is an `istream*' object pointer and not a `FILE*)', +`yy_flush_buffer()', `yy_delete_buffer()', and `yyrestart()' (again, +the first argument is a `istream*' object pointer). + + The second class defined in `FlexLexer.h' is `yyFlexLexer', which is +derived from `FlexLexer'. It defines the following additional member +functions: + +`yyFlexLexer( istream* arg_yyin = 0, ostream* arg_yyout = 0 )' + constructs a `yyFlexLexer' object using the given streams for input + and output. If not specified, the streams default to `cin' and + `cout', respectively. + +`virtual int yylex()' + performs the same role is `yylex()' does for ordinary `flex' + scanners: it scans the input stream, consuming tokens, until a + rule's action returns a value. If you derive a subclass `S' from + `yyFlexLexer' and want to access the member functions and variables + of `S' inside `yylex()', then you need to use `%option + yyclass="S"' to inform `flex' that you will be using that subclass + instead of `yyFlexLexer'. In this case, rather than generating + `yyFlexLexer::yylex()', `flex' generates `S::yylex()' (and also + generates a dummy `yyFlexLexer::yylex()' that calls + `yyFlexLexer::LexerError()' if called). + +`virtual void switch_streams(istream* new_in = 0, ostream* new_out = 0)' + reassigns `yyin' to `new_in' (if non-null) and `yyout' to + `new_out' (if non-null), deleting the previous input buffer if + `yyin' is reassigned. + +`int yylex( istream* new_in, ostream* new_out = 0 )' + first switches the input streams via `switch_streams( new_in, + new_out )' and then returns the value of `yylex()'. + + In addition, `yyFlexLexer' defines the following protected virtual +functions which you can redefine in derived classes to tailor the +scanner: + +`virtual int LexerInput( char* buf, int max_size )' + reads up to `max_size' characters into `buf' and returns the + number of characters read. To indicate end-of-input, return 0 + characters. Note that `interactive' scanners (see the `-B' and + `-I' flags in *Note Scanner Options::) define the macro + `YY_INTERACTIVE'. If you redefine `LexerInput()' and need to take + different actions depending on whether or not the scanner might be + scanning an interactive input source, you can test for the + presence of this name via `#ifdef' statements. + +`virtual void LexerOutput( const char* buf, int size )' + writes out `size' characters from the buffer `buf', which, while + `NUL'-terminated, may also contain internal `NUL's if the + scanner's rules can match text with `NUL's in them. + +`virtual void LexerError( const char* msg )' + reports a fatal error message. The default version of this + function writes the message to the stream `cerr' and exits. + + Note that a `yyFlexLexer' object contains its _entire_ scanning +state. Thus you can use such objects to create reentrant scanners, but +see also *Note Reentrant::. You can instantiate multiple instances of +the same `yyFlexLexer' class, and you can also combine multiple C++ +scanner classes together in the same program using the `-P' option +discussed above. + + Finally, note that the `%array' feature is not available to C++ +scanner classes; you must use `%pointer' (the default). + + Here is an example of a simple C++ scanner: + + + // An example of using the flex C++ scanner class. + + %{ + int mylineno = 0; + %} + + string \"[^\n"]+\" + + ws [ \t]+ + + alpha [A-Za-z] + dig [0-9] + name ({alpha}|{dig}|\$)({alpha}|{dig}|[_.\-/$])* + num1 [-+]?{dig}+\.?([eE][-+]?{dig}+)? + num2 [-+]?{dig}*\.{dig}+([eE][-+]?{dig}+)? + number {num1}|{num2} + + %% + + {ws} /* skip blanks and tabs */ + + "/*" { + int c; + + while((c = yyinput()) != 0) + { + if(c == '\n') + ++mylineno; + + else if(c == @samp{*}) + { + if((c = yyinput()) == '/') + break; + else + unput(c); + } + } + } + + {number} cout "number " YYText() '\n'; + + \n mylineno++; + + {name} cout "name " YYText() '\n'; + + {string} cout "string " YYText() '\n'; + + %% + + int main( int /* argc */, char** /* argv */ ) + { + @code{flex}Lexer* lexer = new yyFlexLexer; + while(lexer->yylex() != 0) + ; + return 0; + } + + If you want to create multiple (different) lexer classes, you use the +`-P' flag (or the `prefix=' option) to rename each `yyFlexLexer' to +some other `xxFlexLexer'. You then can include `<FlexLexer.h>' in your +other sources once per lexer class, first renaming `yyFlexLexer' as +follows: + + + #undef yyFlexLexer + #define yyFlexLexer xxFlexLexer + #include <FlexLexer.h> + + #undef yyFlexLexer + #define yyFlexLexer zzFlexLexer + #include <FlexLexer.h> + + if, for example, you used `%option prefix="xx"' for one of your +scanners and `%option prefix="zz"' for the other. + + +File: flex.info, Node: Reentrant, Next: Lex and Posix, Prev: Cxx, Up: Top + +19 Reentrant C Scanners +*********************** + +`flex' has the ability to generate a reentrant C scanner. This is +accomplished by specifying `%option reentrant' (`-R') The generated +scanner is both portable, and safe to use in one or more separate +threads of control. The most common use for reentrant scanners is from +within multi-threaded applications. Any thread may create and execute +a reentrant `flex' scanner without the need for synchronization with +other threads. + +* Menu: + +* Reentrant Uses:: +* Reentrant Overview:: +* Reentrant Example:: +* Reentrant Detail:: +* Reentrant Functions:: + + +File: flex.info, Node: Reentrant Uses, Next: Reentrant Overview, Prev: Reentrant, Up: Reentrant + +19.1 Uses for Reentrant Scanners +================================ + +However, there are other uses for a reentrant scanner. For example, you +could scan two or more files simultaneously to implement a `diff' at +the token level (i.e., instead of at the character level): + + + /* Example of maintaining more than one active scanner. */ + + do { + int tok1, tok2; + + tok1 = yylex( scanner_1 ); + tok2 = yylex( scanner_2 ); + + if( tok1 != tok2 ) + printf("Files are different."); + + } while ( tok1 && tok2 ); + + Another use for a reentrant scanner is recursion. (Note that a +recursive scanner can also be created using a non-reentrant scanner and +buffer states. *Note Multiple Input Buffers::.) + + The following crude scanner supports the `eval' command by invoking +another instance of itself. + + + /* Example of recursive invocation. */ + + %option reentrant + + %% + "eval(".+")" { + yyscan_t scanner; + YY_BUFFER_STATE buf; + + yylex_init( &scanner ); + yytext[yyleng-1] = ' '; + + buf = yy_scan_string( yytext + 5, scanner ); + yylex( scanner ); + + yy_delete_buffer(buf,scanner); + yylex_destroy( scanner ); + } + ... + %% + + +File: flex.info, Node: Reentrant Overview, Next: Reentrant Example, Prev: Reentrant Uses, Up: Reentrant + +19.2 An Overview of the Reentrant API +===================================== + +The API for reentrant scanners is different than for non-reentrant +scanners. Here is a quick overview of the API: + + `%option reentrant' must be specified. + + * All functions take one additional argument: `yyscanner' + + * All global variables are replaced by their macro equivalents. (We + tell you this because it may be important to you during debugging.) + + * `yylex_init' and `yylex_destroy' must be called before and after + `yylex', respectively. + + * Accessor methods (get/set functions) provide access to common + `flex' variables. + + * User-specific data can be stored in `yyextra'. + + +File: flex.info, Node: Reentrant Example, Next: Reentrant Detail, Prev: Reentrant Overview, Up: Reentrant + +19.3 Reentrant Example +====================== + +First, an example of a reentrant scanner: + + /* This scanner prints "//" comments. */ + + %option reentrant stack noyywrap + %x COMMENT + + %% + + "//" yy_push_state( COMMENT, yyscanner); + .|\n + + <COMMENT>\n yy_pop_state( yyscanner ); + <COMMENT>[^\n]+ fprintf( yyout, "%s\n", yytext); + + %% + + int main ( int argc, char * argv[] ) + { + yyscan_t scanner; + + yylex_init ( &scanner ); + yylex ( scanner ); + yylex_destroy ( scanner ); + return 0; + } + + +File: flex.info, Node: Reentrant Detail, Next: Reentrant Functions, Prev: Reentrant Example, Up: Reentrant + +19.4 The Reentrant API in Detail +================================ + +Here are the things you need to do or know to use the reentrant C API of +`flex'. + +* Menu: + +* Specify Reentrant:: +* Extra Reentrant Argument:: +* Global Replacement:: +* Init and Destroy Functions:: +* Accessor Methods:: +* Extra Data:: +* About yyscan_t:: + + +File: flex.info, Node: Specify Reentrant, Next: Extra Reentrant Argument, Prev: Reentrant Detail, Up: Reentrant Detail + +19.4.1 Declaring a Scanner As Reentrant +--------------------------------------- + +%option reentrant (-reentrant) must be specified. + + Notice that `%option reentrant' is specified in the above example +(*note Reentrant Example::. Had this option not been specified, `flex' +would have happily generated a non-reentrant scanner without +complaining. You may explicitly specify `%option noreentrant', if you +do _not_ want a reentrant scanner, although it is not necessary. The +default is to generate a non-reentrant scanner. + + +File: flex.info, Node: Extra Reentrant Argument, Next: Global Replacement, Prev: Specify Reentrant, Up: Reentrant Detail + +19.4.2 The Extra Argument +------------------------- + +All functions take one additional argument: `yyscanner'. + + Notice that the calls to `yy_push_state' and `yy_pop_state' both +have an argument, `yyscanner' , that is not present in a non-reentrant +scanner. Here are the declarations of `yy_push_state' and +`yy_pop_state' in the reentrant scanner: + + + static void yy_push_state ( int new_state , yyscan_t yyscanner ) ; + static void yy_pop_state ( yyscan_t yyscanner ) ; + + Notice that the argument `yyscanner' appears in the declaration of +both functions. In fact, all `flex' functions in a reentrant scanner +have this additional argument. It is always the last argument in the +argument list, it is always of type `yyscan_t' (which is typedef'd to +`void *') and it is always named `yyscanner'. As you may have guessed, +`yyscanner' is a pointer to an opaque data structure encapsulating the +current state of the scanner. For a list of function declarations, see +*Note Reentrant Functions::. Note that preprocessor macros, such as +`BEGIN', `ECHO', and `REJECT', do not take this additional argument. + + +File: flex.info, Node: Global Replacement, Next: Init and Destroy Functions, Prev: Extra Reentrant Argument, Up: Reentrant Detail + +19.4.3 Global Variables Replaced By Macros +------------------------------------------ + +All global variables in traditional flex have been replaced by macro +equivalents. + + Note that in the above example, `yyout' and `yytext' are not plain +variables. These are macros that will expand to their equivalent lvalue. +All of the familiar `flex' globals have been replaced by their macro +equivalents. In particular, `yytext', `yyleng', `yylineno', `yyin', +`yyout', `yyextra', `yylval', and `yylloc' are macros. You may safely +use these macros in actions as if they were plain variables. We only +tell you this so you don't expect to link to these variables +externally. Currently, each macro expands to a member of an internal +struct, e.g., + + + #define yytext (((struct yyguts_t*)yyscanner)->yytext_r) + + One important thing to remember about `yytext' and friends is that +`yytext' is not a global variable in a reentrant scanner, you can not +access it directly from outside an action or from other functions. You +must use an accessor method, e.g., `yyget_text', to accomplish this. +(See below). + + +File: flex.info, Node: Init and Destroy Functions, Next: Accessor Methods, Prev: Global Replacement, Up: Reentrant Detail + +19.4.4 Init and Destroy Functions +--------------------------------- + +`yylex_init' and `yylex_destroy' must be called before and after +`yylex', respectively. + + + int yylex_init ( yyscan_t * ptr_yy_globals ) ; + int yylex_init_extra ( YY_EXTRA_TYPE user_defined, yyscan_t * ptr_yy_globals ) ; + int yylex ( yyscan_t yyscanner ) ; + int yylex_destroy ( yyscan_t yyscanner ) ; + + The function `yylex_init' must be called before calling any other +function. The argument to `yylex_init' is the address of an +uninitialized pointer to be filled in by `yylex_init', overwriting any +previous contents. The function `yylex_init_extra' may be used instead, +taking as its first argument a variable of type `YY_EXTRA_TYPE'. See +the section on yyextra, below, for more details. + + The value stored in `ptr_yy_globals' should thereafter be passed to +`yylex' and `yylex_destroy'. Flex does not save the argument passed to +`yylex_init', so it is safe to pass the address of a local pointer to +`yylex_init' so long as it remains in scope for the duration of all +calls to the scanner, up to and including the call to `yylex_destroy'. + + The function `yylex' should be familiar to you by now. The reentrant +version takes one argument, which is the value returned (via an +argument) by `yylex_init'. Otherwise, it behaves the same as the +non-reentrant version of `yylex'. + + Both `yylex_init' and `yylex_init_extra' returns 0 (zero) on success, +or non-zero on failure, in which case errno is set to one of the +following values: + + * ENOMEM Memory allocation error. *Note memory-management::. + + * EINVAL Invalid argument. + + The function `yylex_destroy' should be called to free resources used +by the scanner. After `yylex_destroy' is called, the contents of +`yyscanner' should not be used. Of course, there is no need to destroy +a scanner if you plan to reuse it. A `flex' scanner (both reentrant +and non-reentrant) may be restarted by calling `yyrestart'. + + Below is an example of a program that creates a scanner, uses it, +then destroys it when done: + + + int main () + { + yyscan_t scanner; + int tok; + + yylex_init(&scanner); + + while ((tok=yylex()) > 0) + printf("tok=%d yytext=%s\n", tok, yyget_text(scanner)); + + yylex_destroy(scanner); + return 0; + } + + +File: flex.info, Node: Accessor Methods, Next: Extra Data, Prev: Init and Destroy Functions, Up: Reentrant Detail + +19.4.5 Accessing Variables with Reentrant Scanners +-------------------------------------------------- + +Accessor methods (get/set functions) provide access to common `flex' +variables. + + Many scanners that you build will be part of a larger project. +Portions of your project will need access to `flex' values, such as +`yytext'. In a non-reentrant scanner, these values are global, so +there is no problem accessing them. However, in a reentrant scanner, +there are no global `flex' values. You can not access them directly. +Instead, you must access `flex' values using accessor methods (get/set +functions). Each accessor method is named `yyget_NAME' or `yyset_NAME', +where `NAME' is the name of the `flex' variable you want. For example: + + + /* Set the last character of yytext to NULL. */ + void chop ( yyscan_t scanner ) + { + int len = yyget_leng( scanner ); + yyget_text( scanner )[len - 1] = '\0'; + } + + The above code may be called from within an action like this: + + + %% + .+\n { chop( yyscanner );} + + You may find that `%option header-file' is particularly useful for +generating prototypes of all the accessor functions. *Note +option-header::. + + +File: flex.info, Node: Extra Data, Next: About yyscan_t, Prev: Accessor Methods, Up: Reentrant Detail + +19.4.6 Extra Data +----------------- + +User-specific data can be stored in `yyextra'. + + In a reentrant scanner, it is unwise to use global variables to +communicate with or maintain state between different pieces of your +program. However, you may need access to external data or invoke +external functions from within the scanner actions. Likewise, you may +need to pass information to your scanner (e.g., open file descriptors, +or database connections). In a non-reentrant scanner, the only way to +do this would be through the use of global variables. `Flex' allows +you to store arbitrary, "extra" data in a scanner. This data is +accessible through the accessor methods `yyget_extra' and `yyset_extra' +from outside the scanner, and through the shortcut macro `yyextra' from +within the scanner itself. They are defined as follows: + + + #define YY_EXTRA_TYPE void* + YY_EXTRA_TYPE yyget_extra ( yyscan_t scanner ); + void yyset_extra ( YY_EXTRA_TYPE arbitrary_data , yyscan_t scanner); + + In addition, an extra form of `yylex_init' is provided, +`yylex_init_extra'. This function is provided so that the yyextra value +can be accessed from within the very first yyalloc, used to allocate +the scanner itself. + + By default, `YY_EXTRA_TYPE' is defined as type `void *'. You may +redefine this type using `%option extra-type="your_type"' in the +scanner: + + + /* An example of overriding YY_EXTRA_TYPE. */ + %{ + #include <sys/stat.h> + #include <unistd.h> + %} + %option reentrant + %option extra-type="struct stat *" + %% + + __filesize__ printf( "%ld", yyextra->st_size ); + __lastmod__ printf( "%ld", yyextra->st_mtime ); + %% + void scan_file( char* filename ) + { + yyscan_t scanner; + struct stat buf; + FILE *in; + + in = fopen( filename, "r" ); + stat( filename, &buf ); + + yylex_init_extra( buf, &scanner ); + yyset_in( in, scanner ); + yylex( scanner ); + yylex_destroy( scanner ); + + fclose( in ); + } + + +File: flex.info, Node: About yyscan_t, Prev: Extra Data, Up: Reentrant Detail + +19.4.7 About yyscan_t +--------------------- + +`yyscan_t' is defined as: + + + typedef void* yyscan_t; + + It is initialized by `yylex_init()' to point to an internal +structure. You should never access this value directly. In particular, +you should never attempt to free it (use `yylex_destroy()' instead.) + + +File: flex.info, Node: Reentrant Functions, Prev: Reentrant Detail, Up: Reentrant + +19.5 Functions and Macros Available in Reentrant C Scanners +=========================================================== + +The following Functions are available in a reentrant scanner: + + + char *yyget_text ( yyscan_t scanner ); + int yyget_leng ( yyscan_t scanner ); + FILE *yyget_in ( yyscan_t scanner ); + FILE *yyget_out ( yyscan_t scanner ); + int yyget_lineno ( yyscan_t scanner ); + YY_EXTRA_TYPE yyget_extra ( yyscan_t scanner ); + int yyget_debug ( yyscan_t scanner ); + + void yyset_debug ( int flag, yyscan_t scanner ); + void yyset_in ( FILE * in_str , yyscan_t scanner ); + void yyset_out ( FILE * out_str , yyscan_t scanner ); + void yyset_lineno ( int line_number , yyscan_t scanner ); + void yyset_extra ( YY_EXTRA_TYPE user_defined , yyscan_t scanner ); + + There are no "set" functions for yytext and yyleng. This is +intentional. + + The following Macro shortcuts are available in actions in a reentrant +scanner: + + + yytext + yyleng + yyin + yyout + yylineno + yyextra + yy_flex_debug + + In a reentrant C scanner, support for yylineno is always present +(i.e., you may access yylineno), but the value is never modified by +`flex' unless `%option yylineno' is enabled. This is to allow the user +to maintain the line count independently of `flex'. + + The following functions and macros are made available when `%option +bison-bridge' (`--bison-bridge') is specified: + + + YYSTYPE * yyget_lval ( yyscan_t scanner ); + void yyset_lval ( YYSTYPE * yylvalp , yyscan_t scanner ); + yylval + + The following functions and macros are made available when `%option +bison-locations' (`--bison-locations') is specified: + + + YYLTYPE *yyget_lloc ( yyscan_t scanner ); + void yyset_lloc ( YYLTYPE * yyllocp , yyscan_t scanner ); + yylloc + + Support for yylval assumes that `YYSTYPE' is a valid type. Support +for yylloc assumes that `YYSLYPE' is a valid type. Typically, these +types are generated by `bison', and are included in section 1 of the +`flex' input. + + +File: flex.info, Node: Lex and Posix, Next: Memory Management, Prev: Reentrant, Up: Top + +20 Incompatibilities with Lex and Posix +*************************************** + +`flex' is a rewrite of the AT&T Unix _lex_ tool (the two +implementations do not share any code, though), with some extensions and +incompatibilities, both of which are of concern to those who wish to +write scanners acceptable to both implementations. `flex' is fully +compliant with the POSIX `lex' specification, except that when using +`%pointer' (the default), a call to `unput()' destroys the contents of +`yytext', which is counter to the POSIX specification. In this section +we discuss all of the known areas of incompatibility between `flex', +AT&T `lex', and the POSIX specification. `flex''s `-l' option turns on +maximum compatibility with the original AT&T `lex' implementation, at +the cost of a major loss in the generated scanner's performance. We +note below which incompatibilities can be overcome using the `-l' +option. `flex' is fully compatible with `lex' with the following +exceptions: + + * The undocumented `lex' scanner internal variable `yylineno' is not + supported unless `-l' or `%option yylineno' is used. + + * `yylineno' should be maintained on a per-buffer basis, rather than + a per-scanner (single global variable) basis. + + * `yylineno' is not part of the POSIX specification. + + * The `input()' routine is not redefinable, though it may be called + to read characters following whatever has been matched by a rule. + If `input()' encounters an end-of-file the normal `yywrap()' + processing is done. A "real" end-of-file is returned by `input()' + as `EOF'. + + * Input is instead controlled by defining the `YY_INPUT()' macro. + + * The `flex' restriction that `input()' cannot be redefined is in + accordance with the POSIX specification, which simply does not + specify any way of controlling the scanner's input other than by + making an initial assignment to `yyin'. + + * The `unput()' routine is not redefinable. This restriction is in + accordance with POSIX. + + * `flex' scanners are not as reentrant as `lex' scanners. In + particular, if you have an interactive scanner and an interrupt + handler which long-jumps out of the scanner, and the scanner is + subsequently called again, you may get the following message: + + + fatal @code{flex} scanner internal error--end of buffer missed + + To reenter the scanner, first use: + + + yyrestart( yyin ); + + Note that this call will throw away any buffered input; usually + this isn't a problem with an interactive scanner. *Note + Reentrant::, for `flex''s reentrant API. + + * Also note that `flex' C++ scanner classes _are_ reentrant, so if + using C++ is an option for you, you should use them instead. + *Note Cxx::, and *Note Reentrant:: for details. + + * `output()' is not supported. Output from the ECHO macro is done + to the file-pointer `yyout' (default `stdout)'. + + * `output()' is not part of the POSIX specification. + + * `lex' does not support exclusive start conditions (%x), though they + are in the POSIX specification. + + * When definitions are expanded, `flex' encloses them in parentheses. + With `lex', the following: + + + NAME [A-Z][A-Z0-9]* + %% + foo{NAME}? printf( "Found it\n" ); + %% + + will not match the string `foo' because when the macro is expanded + the rule is equivalent to `foo[A-Z][A-Z0-9]*?' and the precedence + is such that the `?' is associated with `[A-Z0-9]*'. With `flex', + the rule will be expanded to `foo([A-Z][A-Z0-9]*)?' and so the + string `foo' will match. + + * Note that if the definition begins with `^' or ends with `$' then + it is _not_ expanded with parentheses, to allow these operators to + appear in definitions without losing their special meanings. But + the `<s>', `/', and `<<EOF>>' operators cannot be used in a `flex' + definition. + + * Using `-l' results in the `lex' behavior of no parentheses around + the definition. + + * The POSIX specification is that the definition be enclosed in + parentheses. + + * Some implementations of `lex' allow a rule's action to begin on a + separate line, if the rule's pattern has trailing whitespace: + + + %% + foo|bar<space here> + { foobar_action();} + + `flex' does not support this feature. + + * The `lex' `%r' (generate a Ratfor scanner) option is not + supported. It is not part of the POSIX specification. + + * After a call to `unput()', _yytext_ is undefined until the next + token is matched, unless the scanner was built using `%array'. + This is not the case with `lex' or the POSIX specification. The + `-l' option does away with this incompatibility. + + * The precedence of the `{,}' (numeric range) operator is different. + The AT&T and POSIX specifications of `lex' interpret `abc{1,3}' + as match one, two, or three occurrences of `abc'", whereas `flex' + interprets it as "match `ab' followed by one, two, or three + occurrences of `c'". The `-l' and `--posix' options do away with + this incompatibility. + + * The precedence of the `^' operator is different. `lex' interprets + `^foo|bar' as "match either 'foo' at the beginning of a line, or + 'bar' anywhere", whereas `flex' interprets it as "match either + `foo' or `bar' if they come at the beginning of a line". The + latter is in agreement with the POSIX specification. + + * The special table-size declarations such as `%a' supported by + `lex' are not required by `flex' scanners.. `flex' ignores them. + + * The name `FLEX_SCANNER' is `#define''d so scanners may be written + for use with either `flex' or `lex'. Scanners also include + `YY_FLEX_MAJOR_VERSION', `YY_FLEX_MINOR_VERSION' and + `YY_FLEX_SUBMINOR_VERSION' indicating which version of `flex' + generated the scanner. For example, for the 2.5.22 release, these + defines would be 2, 5 and 22 respectively. If the version of + `flex' being used is a beta version, then the symbol `FLEX_BETA' + is defined. + + * The symbols `[[' and `]]' in the code sections of the input may + conflict with the m4 delimiters. *Note M4 Dependency::. + + + The following `flex' features are not included in `lex' or the POSIX +specification: + + * C++ scanners + + * %option + + * start condition scopes + + * start condition stacks + + * interactive/non-interactive scanners + + * yy_scan_string() and friends + + * yyterminate() + + * yy_set_interactive() + + * yy_set_bol() + + * YY_AT_BOL() <<EOF>> + + * <*> + + * YY_DECL + + * YY_START + + * YY_USER_ACTION + + * YY_USER_INIT + + * #line directives + + * %{}'s around actions + + * reentrant C API + + * multiple actions on a line + + * almost all of the `flex' command-line options + + The feature "multiple actions on a line" refers to the fact that +with `flex' you can put multiple actions on the same line, separated +with semi-colons, while with `lex', the following: + + + foo handle_foo(); ++num_foos_seen; + + is (rather surprisingly) truncated to + + + foo handle_foo(); + + `flex' does not truncate the action. Actions that are not enclosed +in braces are simply terminated at the end of the line. + + +File: flex.info, Node: Memory Management, Next: Serialized Tables, Prev: Lex and Posix, Up: Top + +21 Memory Management +******************** + +This chapter describes how flex handles dynamic memory, and how you can +override the default behavior. + +* Menu: + +* The Default Memory Management:: +* Overriding The Default Memory Management:: +* A Note About yytext And Memory:: + + +File: flex.info, Node: The Default Memory Management, Next: Overriding The Default Memory Management, Prev: Memory Management, Up: Memory Management + +21.1 The Default Memory Management +================================== + +Flex allocates dynamic memory during initialization, and once in a +while from within a call to yylex(). Initialization takes place during +the first call to yylex(). Thereafter, flex may reallocate more memory +if it needs to enlarge a buffer. As of version 2.5.9 Flex will clean up +all memory when you call `yylex_destroy' *Note faq-memory-leak::. + + Flex allocates dynamic memory for four purposes, listed below (1) + +16kB for the input buffer. + Flex allocates memory for the character buffer used to perform + pattern matching. Flex must read ahead from the input stream and + store it in a large character buffer. This buffer is typically + the largest chunk of dynamic memory flex consumes. This buffer + will grow if necessary, doubling the size each time. Flex frees + this memory when you call yylex_destroy(). The default size of + this buffer (16384 bytes) is almost always too large. The ideal + size for this buffer is the length of the longest token expected, + in bytes, plus a little more. Flex will allocate a few extra + bytes for housekeeping. Currently, to override the size of the + input buffer you must `#define YY_BUF_SIZE' to whatever number of + bytes you want. We don't plan to change this in the near future, + but we reserve the right to do so if we ever add a more robust + memory management API. + +64kb for the REJECT state. This will only be allocated if you use REJECT. + The size is the large enough to hold the same number of states as + characters in the input buffer. If you override the size of the + input buffer (via `YY_BUF_SIZE'), then you automatically override + the size of this buffer as well. + +100 bytes for the start condition stack. + Flex allocates memory for the start condition stack. This is the + stack used for pushing start states, i.e., with yy_push_state(). + It will grow if necessary. Since the states are simply integers, + this stack doesn't consume much memory. This stack is not present + if `%option stack' is not specified. You will rarely need to tune + this buffer. The ideal size for this stack is the maximum depth + expected. The memory for this stack is automatically destroyed + when you call yylex_destroy(). *Note option-stack::. + +40 bytes for each YY_BUFFER_STATE. + Flex allocates memory for each YY_BUFFER_STATE. The buffer state + itself is about 40 bytes, plus an additional large character + buffer (described above.) The initial buffer state is created + during initialization, and with each call to yy_create_buffer(). + You can't tune the size of this, but you can tune the character + buffer as described above. Any buffer state that you explicitly + create by calling yy_create_buffer() is _NOT_ destroyed + automatically. You must call yy_delete_buffer() to free the + memory. The exception to this rule is that flex will delete the + current buffer automatically when you call yylex_destroy(). If you + delete the current buffer, be sure to set it to NULL. That way, + flex will not try to delete the buffer a second time (possibly + crashing your program!) At the time of this writing, flex does not + provide a growable stack for the buffer states. You have to + manage that yourself. *Note Multiple Input Buffers::. + +84 bytes for the reentrant scanner guts + Flex allocates about 84 bytes for the reentrant scanner structure + when you call yylex_init(). It is destroyed when the user calls + yylex_destroy(). + + + ---------- Footnotes ---------- + + (1) The quantities given here are approximate, and may vary due to +host architecture, compiler configuration, or due to future +enhancements to flex. + + +File: flex.info, Node: Overriding The Default Memory Management, Next: A Note About yytext And Memory, Prev: The Default Memory Management, Up: Memory Management + +21.2 Overriding The Default Memory Management +============================================= + +Flex calls the functions `yyalloc', `yyrealloc', and `yyfree' when it +needs to allocate or free memory. By default, these functions are +wrappers around the standard C functions, `malloc', `realloc', and +`free', respectively. You can override the default implementations by +telling flex that you will provide your own implementations. + + To override the default implementations, you must do two things: + + 1. Suppress the default implementations by specifying one or more of + the following options: + + * `%option noyyalloc' + + * `%option noyyrealloc' + + * `%option noyyfree'. + + 2. Provide your own implementation of the following functions: (1) + + + // For a non-reentrant scanner + void * yyalloc (size_t bytes); + void * yyrealloc (void * ptr, size_t bytes); + void yyfree (void * ptr); + + // For a reentrant scanner + void * yyalloc (size_t bytes, void * yyscanner); + void * yyrealloc (void * ptr, size_t bytes, void * yyscanner); + void yyfree (void * ptr, void * yyscanner); + + + In the following example, we will override all three memory +routines. We assume that there is a custom allocator with garbage +collection. In order to make this example interesting, we will use a +reentrant scanner, passing a pointer to the custom allocator through +`yyextra'. + + + %{ + #include "some_allocator.h" + %} + + /* Suppress the default implementations. */ + %option noyyalloc noyyrealloc noyyfree + %option reentrant + + /* Initialize the allocator. */ + #define YY_EXTRA_TYPE struct allocator* + #define YY_USER_INIT yyextra = allocator_create(); + + %% + .|\n ; + %% + + /* Provide our own implementations. */ + void * yyalloc (size_t bytes, void* yyscanner) { + return allocator_alloc (yyextra, bytes); + } + + void * yyrealloc (void * ptr, size_t bytes, void* yyscanner) { + return allocator_realloc (yyextra, bytes); + } + + void yyfree (void * ptr, void * yyscanner) { + /* Do nothing -- we leave it to the garbage collector. */ + } + + ---------- Footnotes ---------- + + (1) It is not necessary to override all (or any) of the memory +management routines. You may, for example, override `yyrealloc', but +not `yyfree' or `yyalloc'. + + +File: flex.info, Node: A Note About yytext And Memory, Prev: Overriding The Default Memory Management, Up: Memory Management + +21.3 A Note About yytext And Memory +=================================== + +When flex finds a match, `yytext' points to the first character of the +match in the input buffer. The string itself is part of the input +buffer, and is _NOT_ allocated separately. The value of yytext will be +overwritten the next time yylex() is called. In short, the value of +yytext is only valid from within the matched rule's action. + + Often, you want the value of yytext to persist for later processing, +i.e., by a parser with non-zero lookahead. In order to preserve yytext, +you will have to copy it with strdup() or a similar function. But this +introduces some headache because your parser is now responsible for +freeing the copy of yytext. If you use a yacc or bison parser, +(commonly used with flex), you will discover that the error recovery +mechanisms can cause memory to be leaked. + + To prevent memory leaks from strdup'd yytext, you will have to track +the memory somehow. Our experience has shown that a garbage collection +mechanism or a pooled memory mechanism will save you a lot of grief +when writing parsers. + + +File: flex.info, Node: Serialized Tables, Next: Diagnostics, Prev: Memory Management, Up: Top + +22 Serialized Tables +******************** + +A `flex' scanner has the ability to save the DFA tables to a file, and +load them at runtime when needed. The motivation for this feature is +to reduce the runtime memory footprint. Traditionally, these tables +have been compiled into the scanner as C arrays, and are sometimes +quite large. Since the tables are compiled into the scanner, the +memory used by the tables can never be freed. This is a waste of +memory, especially if an application uses several scanners, but none of +them at the same time. + + The serialization feature allows the tables to be loaded at runtime, +before scanning begins. The tables may be discarded when scanning is +finished. + +* Menu: + +* Creating Serialized Tables:: +* Loading and Unloading Serialized Tables:: +* Tables File Format:: + + +File: flex.info, Node: Creating Serialized Tables, Next: Loading and Unloading Serialized Tables, Prev: Serialized Tables, Up: Serialized Tables + +22.1 Creating Serialized Tables +=============================== + +You may create a scanner with serialized tables by specifying: + + + %option tables-file=FILE + or + --tables-file=FILE + + These options instruct flex to save the DFA tables to the file FILE. +The tables will _not_ be embedded in the generated scanner. The scanner +will not function on its own. The scanner will be dependent upon the +serialized tables. You must load the tables from this file at runtime +before you can scan anything. + + If you do not specify a filename to `--tables-file', the tables will +be saved to `lex.yy.tables', where `yy' is the appropriate prefix. + + If your project uses several different scanners, you can concatenate +the serialized tables into one file, and flex will find the correct set +of tables, using the scanner prefix as part of the lookup key. An +example follows: + + + $ flex --tables-file --prefix=cpp cpp.l + $ flex --tables-file --prefix=c c.l + $ cat lex.cpp.tables lex.c.tables > all.tables + + The above example created two scanners, `cpp', and `c'. Since we did +not specify a filename, the tables were serialized to `lex.c.tables' and +`lex.cpp.tables', respectively. Then, we concatenated the two files +together into `all.tables', which we will distribute with our project. +At runtime, we will open the file and tell flex to load the tables from +it. Flex will find the correct tables automatically. (See next +section). + + +File: flex.info, Node: Loading and Unloading Serialized Tables, Next: Tables File Format, Prev: Creating Serialized Tables, Up: Serialized Tables + +22.2 Loading and Unloading Serialized Tables +============================================ + +If you've built your scanner with `%option tables-file', then you must +load the scanner tables at runtime. This can be accomplished with the +following function: + + -- Function: int yytables_fload (FILE* FP [, yyscan_t SCANNER]) + Locates scanner tables in the stream pointed to by FP and loads + them. Memory for the tables is allocated via `yyalloc'. You must + call this function before the first call to `yylex'. The argument + SCANNER only appears in the reentrant scanner. This function + returns `0' (zero) on success, or non-zero on error. + + The loaded tables are *not* automatically destroyed (unloaded) when +you call `yylex_destroy'. The reason is that you may create several +scanners of the same type (in a reentrant scanner), each of which needs +access to these tables. To avoid a nasty memory leak, you must call +the following function: + + -- Function: int yytables_destroy ([yyscan_t SCANNER]) + Unloads the scanner tables. The tables must be loaded again before + you can scan any more data. The argument SCANNER only appears in + the reentrant scanner. This function returns `0' (zero) on + success, or non-zero on error. + + *The functions `yytables_fload' and `yytables_destroy' are not +thread-safe.* You must ensure that these functions are called exactly +once (for each scanner type) in a threaded program, before any thread +calls `yylex'. After the tables are loaded, they are never written to, +and no thread protection is required thereafter - until you destroy +them. + + +File: flex.info, Node: Tables File Format, Prev: Loading and Unloading Serialized Tables, Up: Serialized Tables + +22.3 Tables File Format +======================= + +This section defines the file format of serialized `flex' tables. + + The tables format allows for one or more sets of tables to be +specified, where each set corresponds to a given scanner. Scanners are +indexed by name, as described below. The file format is as follows: + + + TABLE SET 1 + +-------------------------------+ + Header | uint32 th_magic; | + | uint32 th_hsize; | + | uint32 th_ssize; | + | uint16 th_flags; | + | char th_version[]; | + | char th_name[]; | + | uint8 th_pad64[]; | + +-------------------------------+ + Table 1 | uint16 td_id; | + | uint16 td_flags; | + | uint32 td_lolen; | + | uint32 td_hilen; | + | void td_data[]; | + | uint8 td_pad64[]; | + +-------------------------------+ + Table 2 | | + . . . + . . . + . . . + . . . + Table n | | + +-------------------------------+ + TABLE SET 2 + . + . + . + TABLE SET N + + The above diagram shows that a complete set of tables consists of a +header followed by multiple individual tables. Furthermore, multiple +complete sets may be present in the same file, each set with its own +header and tables. The sets are contiguous in the file. The only way to +know if another set follows is to check the next four bytes for the +magic number (or check for EOF). The header and tables sections are +padded to 64-bit boundaries. Below we describe each field in detail. +This format does not specify how the scanner will expand the given +data, i.e., data may be serialized as int8, but expanded to an int32 +array at runtime. This is to reduce the size of the serialized data +where possible. Remember, _all integer values are in network byte +order_. + +Fields of a table header: + +`th_magic' + Magic number, always 0xF13C57B1. + +`th_hsize' + Size of this entire header, in bytes, including all fields plus + any padding. + +`th_ssize' + Size of this entire set, in bytes, including the header, all + tables, plus any padding. + +`th_flags' + Bit flags for this table set. Currently unused. + +`th_version[]' + Flex version in NULL-terminated string format. e.g., `2.5.13a'. + This is the version of flex that was used to create the serialized + tables. + +`th_name[]' + Contains the name of this table set. The default is `yytables', + and is prefixed accordingly, e.g., `footables'. Must be + NULL-terminated. + +`th_pad64[]' + Zero or more NULL bytes, padding the entire header to the next + 64-bit boundary as calculated from the beginning of the header. + +Fields of a table: + +`td_id' + Specifies the table identifier. Possible values are: + `YYTD_ID_ACCEPT (0x01)' + `yy_accept' + + `YYTD_ID_BASE (0x02)' + `yy_base' + + `YYTD_ID_CHK (0x03)' + `yy_chk' + + `YYTD_ID_DEF (0x04)' + `yy_def' + + `YYTD_ID_EC (0x05)' + `yy_ec ' + + `YYTD_ID_META (0x06)' + `yy_meta' + + `YYTD_ID_NUL_TRANS (0x07)' + `yy_NUL_trans' + + `YYTD_ID_NXT (0x08)' + `yy_nxt'. This array may be two dimensional. See the + `td_hilen' field below. + + `YYTD_ID_RULE_CAN_MATCH_EOL (0x09)' + `yy_rule_can_match_eol' + + `YYTD_ID_START_STATE_LIST (0x0A)' + `yy_start_state_list'. This array is handled specially + because it is an array of pointers to structs. See the + `td_flags' field below. + + `YYTD_ID_TRANSITION (0x0B)' + `yy_transition'. This array is handled specially because it + is an array of structs. See the `td_lolen' field below. + + `YYTD_ID_ACCLIST (0x0C)' + `yy_acclist' + +`td_flags' + Bit flags describing how to interpret the data in `td_data'. The + data arrays are one-dimensional by default, but may be two + dimensional as specified in the `td_hilen' field. + + `YYTD_DATA8 (0x01)' + The data is serialized as an array of type int8. + + `YYTD_DATA16 (0x02)' + The data is serialized as an array of type int16. + + `YYTD_DATA32 (0x04)' + The data is serialized as an array of type int32. + + `YYTD_PTRANS (0x08)' + The data is a list of indexes of entries in the expanded + `yy_transition' array. Each index should be expanded to a + pointer to the corresponding entry in the `yy_transition' + array. We count on the fact that the `yy_transition' array + has already been seen. + + `YYTD_STRUCT (0x10)' + The data is a list of yy_trans_info structs, each of which + consists of two integers. There is no padding between struct + elements or between structs. The type of each member is + determined by the `YYTD_DATA*' bits. + +`td_lolen' + Specifies the number of elements in the lowest dimension array. If + this is a one-dimensional array, then it is simply the number of + elements in this array. The element size is determined by the + `td_flags' field. + +`td_hilen' + If `td_hilen' is non-zero, then the data is a two-dimensional + array. Otherwise, the data is a one-dimensional array. `td_hilen' + contains the number of elements in the higher dimensional array, + and `td_lolen' contains the number of elements in the lowest + dimension. + + Conceptually, `td_data' is either `sometype td_data[td_lolen]', or + `sometype td_data[td_hilen][td_lolen]', where `sometype' is + specified by the `td_flags' field. It is possible for both + `td_lolen' and `td_hilen' to be zero, in which case `td_data' is a + zero length array, and no data is loaded, i.e., this table is + simply skipped. Flex does not currently generate tables of zero + length. + +`td_data[]' + The table data. This array may be a one- or two-dimensional array, + of type `int8', `int16', `int32', `struct yy_trans_info', or + `struct yy_trans_info*', depending upon the values in the + `td_flags', `td_lolen', and `td_hilen' fields. + +`td_pad64[]' + Zero or more NULL bytes, padding the entire table to the next + 64-bit boundary as calculated from the beginning of this table. + + +File: flex.info, Node: Diagnostics, Next: Limitations, Prev: Serialized Tables, Up: Top + +23 Diagnostics +************** + +The following is a list of `flex' diagnostic messages: + + * `warning, rule cannot be matched' indicates that the given rule + cannot be matched because it follows other rules that will always + match the same text as it. For example, in the following `foo' + cannot be matched because it comes after an identifier "catch-all" + rule: + + + [a-z]+ got_identifier(); + foo got_foo(); + + Using `REJECT' in a scanner suppresses this warning. + + * `warning, -s option given but default rule can be matched' means + that it is possible (perhaps only in a particular start condition) + that the default rule (match any single character) is the only one + that will match a particular input. Since `-s' was given, + presumably this is not intended. + + * `reject_used_but_not_detected undefined' or + `yymore_used_but_not_detected undefined'. These errors can occur + at compile time. They indicate that the scanner uses `REJECT' or + `yymore()' but that `flex' failed to notice the fact, meaning that + `flex' scanned the first two sections looking for occurrences of + these actions and failed to find any, but somehow you snuck some in + (via a #include file, for example). Use `%option reject' or + `%option yymore' to indicate to `flex' that you really do use + these features. + + * `flex scanner jammed'. a scanner compiled with `-s' has + encountered an input string which wasn't matched by any of its + rules. This error can also occur due to internal problems. + + * `token too large, exceeds YYLMAX'. your scanner uses `%array' and + one of its rules matched a string longer than the `YYLMAX' + constant (8K bytes by default). You can increase the value by + #define'ing `YYLMAX' in the definitions section of your `flex' + input. + + * `scanner requires -8 flag to use the character 'x''. Your scanner + specification includes recognizing the 8-bit character `'x'' and + you did not specify the -8 flag, and your scanner defaulted to + 7-bit because you used the `-Cf' or `-CF' table compression + options. See the discussion of the `-7' flag, *Note Scanner + Options::, for details. + + * `flex scanner push-back overflow'. you used `unput()' to push back + so much text that the scanner's buffer could not hold both the + pushed-back text and the current token in `yytext'. Ideally the + scanner should dynamically resize the buffer in this case, but at + present it does not. + + * `input buffer overflow, can't enlarge buffer because scanner uses + REJECT'. the scanner was working on matching an extremely large + token and needed to expand the input buffer. This doesn't work + with scanners that use `REJECT'. + + * `fatal flex scanner internal error--end of buffer missed'. This can + occur in a scanner which is reentered after a long-jump has jumped + out (or over) the scanner's activation frame. Before reentering + the scanner, use: + + yyrestart( yyin ); + or, as noted above, switch to using the C++ scanner class. + + * `too many start conditions in <> construct!' you listed more start + conditions in a <> construct than exist (so you must have listed at + least one of them twice). + + +File: flex.info, Node: Limitations, Next: Bibliography, Prev: Diagnostics, Up: Top + +24 Limitations +************** + +Some trailing context patterns cannot be properly matched and generate +warning messages (`dangerous trailing context'). These are patterns +where the ending of the first part of the rule matches the beginning of +the second part, such as `zx*/xy*', where the 'x*' matches the 'x' at +the beginning of the trailing context. (Note that the POSIX draft +states that the text matched by such patterns is undefined.) For some +trailing context rules, parts which are actually fixed-length are not +recognized as such, leading to the abovementioned performance loss. In +particular, parts using `|' or `{n}' (such as `foo{3}') are always +considered variable-length. Combining trailing context with the +special `|' action can result in _fixed_ trailing context being turned +into the more expensive _variable_ trailing context. For example, in +the following: + + + %% + abc | + xyz/def + + Use of `unput()' invalidates yytext and yyleng, unless the `%array' +directive or the `-l' option has been used. Pattern-matching of `NUL's +is substantially slower than matching other characters. Dynamic +resizing of the input buffer is slow, as it entails rescanning all the +text matched so far by the current (generally huge) token. Due to both +buffering of input and read-ahead, you cannot intermix calls to +`<stdio.h>' routines, such as, getchar(), with `flex' rules and expect +it to work. Call `input()' instead. The total table entries listed by +the `-v' flag excludes the number of table entries needed to determine +what rule has been matched. The number of entries is equal to the +number of DFA states if the scanner does not use `REJECT', and somewhat +greater than the number of states if it does. `REJECT' cannot be used +with the `-f' or `-F' options. + + The `flex' internal algorithms need documentation. + + +File: flex.info, Node: Bibliography, Next: FAQ, Prev: Limitations, Up: Top + +25 Additional Reading +********************* + +You may wish to read more about the following programs: + * lex + + * yacc + + * sed + + * awk + + The following books may contain material of interest: + + John Levine, Tony Mason, and Doug Brown, _Lex & Yacc_, O'Reilly and +Associates. Be sure to get the 2nd edition. + + M. E. Lesk and E. Schmidt, _LEX - Lexical Analyzer Generator_ + + Alfred Aho, Ravi Sethi and Jeffrey Ullman, _Compilers: Principles, +Techniques and Tools_, Addison-Wesley (1986). Describes the +pattern-matching techniques used by `flex' (deterministic finite +automata). + + +File: flex.info, Node: FAQ, Next: Appendices, Prev: Bibliography, Up: Top + +FAQ +*** + +From time to time, the `flex' maintainer receives certain questions. +Rather than repeat answers to well-understood problems, we publish them +here. + +* Menu: + +* When was flex born?:: +* How do I expand backslash-escape sequences in C-style quoted strings?:: +* Why do flex scanners call fileno if it is not ANSI compatible?:: +* Does flex support recursive pattern definitions?:: +* How do I skip huge chunks of input (tens of megabytes) while using flex?:: +* Flex is not matching my patterns in the same order that I defined them.:: +* My actions are executing out of order or sometimes not at all.:: +* How can I have multiple input sources feed into the same scanner at the same time?:: +* Can I build nested parsers that work with the same input file?:: +* How can I match text only at the end of a file?:: +* How can I make REJECT cascade across start condition boundaries?:: +* Why cant I use fast or full tables with interactive mode?:: +* How much faster is -F or -f than -C?:: +* If I have a simple grammar cant I just parse it with flex?:: +* Why doesn't yyrestart() set the start state back to INITIAL?:: +* How can I match C-style comments?:: +* The period isn't working the way I expected.:: +* Can I get the flex manual in another format?:: +* Does there exist a "faster" NDFA->DFA algorithm?:: +* How does flex compile the DFA so quickly?:: +* How can I use more than 8192 rules?:: +* How do I abandon a file in the middle of a scan and switch to a new file?:: +* How do I execute code only during initialization (only before the first scan)?:: +* How do I execute code at termination?:: +* Where else can I find help?:: +* Can I include comments in the "rules" section of the file?:: +* I get an error about undefined yywrap().:: +* How can I change the matching pattern at run time?:: +* How can I expand macros in the input?:: +* How can I build a two-pass scanner?:: +* How do I match any string not matched in the preceding rules?:: +* I am trying to port code from AT&T lex that uses yysptr and yysbuf.:: +* Is there a way to make flex treat NULL like a regular character?:: +* Whenever flex can not match the input it says "flex scanner jammed".:: +* Why doesn't flex have non-greedy operators like perl does?:: +* Memory leak - 16386 bytes allocated by malloc.:: +* How do I track the byte offset for lseek()?:: +* How do I use my own I/O classes in a C++ scanner?:: +* How do I skip as many chars as possible?:: +* deleteme00:: +* Are certain equivalent patterns faster than others?:: +* Is backing up a big deal?:: +* Can I fake multi-byte character support?:: +* deleteme01:: +* Can you discuss some flex internals?:: +* unput() messes up yy_at_bol:: +* The | operator is not doing what I want:: +* Why can't flex understand this variable trailing context pattern?:: +* The ^ operator isn't working:: +* Trailing context is getting confused with trailing optional patterns:: +* Is flex GNU or not?:: +* ERASEME53:: +* I need to scan if-then-else blocks and while loops:: +* ERASEME55:: +* ERASEME56:: +* ERASEME57:: +* Is there a repository for flex scanners?:: +* How can I conditionally compile or preprocess my flex input file?:: +* Where can I find grammars for lex and yacc?:: +* I get an end-of-buffer message for each character scanned.:: +* unnamed-faq-62:: +* unnamed-faq-63:: +* unnamed-faq-64:: +* unnamed-faq-65:: +* unnamed-faq-66:: +* unnamed-faq-67:: +* unnamed-faq-68:: +* unnamed-faq-69:: +* unnamed-faq-70:: +* unnamed-faq-71:: +* unnamed-faq-72:: +* unnamed-faq-73:: +* unnamed-faq-74:: +* unnamed-faq-75:: +* unnamed-faq-76:: +* unnamed-faq-77:: +* unnamed-faq-78:: +* unnamed-faq-79:: +* unnamed-faq-80:: +* unnamed-faq-81:: +* unnamed-faq-82:: +* unnamed-faq-83:: +* unnamed-faq-84:: +* unnamed-faq-85:: +* unnamed-faq-86:: +* unnamed-faq-87:: +* unnamed-faq-88:: +* unnamed-faq-90:: +* unnamed-faq-91:: +* unnamed-faq-92:: +* unnamed-faq-93:: +* unnamed-faq-94:: +* unnamed-faq-95:: +* unnamed-faq-96:: +* unnamed-faq-97:: +* unnamed-faq-98:: +* unnamed-faq-99:: +* unnamed-faq-100:: +* unnamed-faq-101:: +* What is the difference between YYLEX_PARAM and YY_DECL?:: +* Why do I get "conflicting types for yylex" error?:: +* How do I access the values set in a Flex action from within a Bison action?:: + + +File: flex.info, Node: When was flex born?, Next: How do I expand backslash-escape sequences in C-style quoted strings?, Up: FAQ + +When was flex born? +=================== + +Vern Paxson took over the `Software Tools' lex project from Jef +Poskanzer in 1982. At that point it was written in Ratfor. Around +1987 or so, Paxson translated it into C, and a legend was born :-). + + +File: flex.info, Node: How do I expand backslash-escape sequences in C-style quoted strings?, Next: Why do flex scanners call fileno if it is not ANSI compatible?, Prev: When was flex born?, Up: FAQ + +How do I expand backslash-escape sequences in C-style quoted strings? +===================================================================== + +A key point when scanning quoted strings is that you cannot (easily) +write a single rule that will precisely match the string if you allow +things like embedded escape sequences and newlines. If you try to +match strings with a single rule then you'll wind up having to rescan +the string anyway to find any escape sequences. + + Instead you can use exclusive start conditions and a set of rules, +one for matching non-escaped text, one for matching a single escape, +one for matching an embedded newline, and one for recognizing the end +of the string. Each of these rules is then faced with the question of +where to put its intermediary results. The best solution is for the +rules to append their local value of `yytext' to the end of a "string +literal" buffer. A rule like the escape-matcher will append to the +buffer the meaning of the escape sequence rather than the literal text +in `yytext'. In this way, `yytext' does not need to be modified at all. + + +File: flex.info, Node: Why do flex scanners call fileno if it is not ANSI compatible?, Next: Does flex support recursive pattern definitions?, Prev: How do I expand backslash-escape sequences in C-style quoted strings?, Up: FAQ + +Why do flex scanners call fileno if it is not ANSI compatible? +============================================================== + +Flex scanners call `fileno()' in order to get the file descriptor +corresponding to `yyin'. The file descriptor may be passed to +`isatty()' or `read()', depending upon which `%options' you specified. +If your system does not have `fileno()' support, to get rid of the +`read()' call, do not specify `%option read'. To get rid of the +`isatty()' call, you must specify one of `%option always-interactive' or +`%option never-interactive'. + + +File: flex.info, Node: Does flex support recursive pattern definitions?, Next: How do I skip huge chunks of input (tens of megabytes) while using flex?, Prev: Why do flex scanners call fileno if it is not ANSI compatible?, Up: FAQ + +Does flex support recursive pattern definitions? +================================================ + +e.g., + + + %% + block "{"({block}|{statement})*"}" + + No. You cannot have recursive definitions. The pattern-matching +power of regular expressions in general (and therefore flex scanners, +too) is limited. In particular, regular expressions cannot "balance" +parentheses to an arbitrary degree. For example, it's impossible to +write a regular expression that matches all strings containing the same +number of '{'s as '}'s. For more powerful pattern matching, you need a +parser, such as `GNU bison'. + + +File: flex.info, Node: How do I skip huge chunks of input (tens of megabytes) while using flex?, Next: Flex is not matching my patterns in the same order that I defined them., Prev: Does flex support recursive pattern definitions?, Up: FAQ + +How do I skip huge chunks of input (tens of megabytes) while using flex? +======================================================================== + +Use `fseek()' (or `lseek()') to position yyin, then call `yyrestart()'. + + +File: flex.info, Node: Flex is not matching my patterns in the same order that I defined them., Next: My actions are executing out of order or sometimes not at all., Prev: How do I skip huge chunks of input (tens of megabytes) while using flex?, Up: FAQ + +Flex is not matching my patterns in the same order that I defined them. +======================================================================= + +`flex' picks the rule that matches the most text (i.e., the longest +possible input string). This is because `flex' uses an entirely +different matching technique ("deterministic finite automata") that +actually does all of the matching simultaneously, in parallel. (Seems +impossible, but it's actually a fairly simple technique once you +understand the principles.) + + A side-effect of this parallel matching is that when the input +matches more than one rule, `flex' scanners pick the rule that matched +the _most_ text. This is explained further in the manual, in the +section *Note Matching::. + + If you want `flex' to choose a shorter match, then you can work +around this behavior by expanding your short rule to match more text, +then put back the extra: + + + data_.* yyless( 5 ); BEGIN BLOCKIDSTATE; + + Another fix would be to make the second rule active only during the +`<BLOCKIDSTATE>' start condition, and make that start condition +exclusive by declaring it with `%x' instead of `%s'. + + A final fix is to change the input language so that the ambiguity for +`data_' is removed, by adding characters to it that don't match the +identifier rule, or by removing characters (such as `_') from the +identifier rule so it no longer matches `data_'. (Of course, you might +also not have the option of changing the input language.) + + +File: flex.info, Node: My actions are executing out of order or sometimes not at all., Next: How can I have multiple input sources feed into the same scanner at the same time?, Prev: Flex is not matching my patterns in the same order that I defined them., Up: FAQ + +My actions are executing out of order or sometimes not at all. +============================================================== + +Most likely, you have (in error) placed the opening `{' of the action +block on a different line than the rule, e.g., + + + ^(foo|bar) + { <<<--- WRONG! + + } + + `flex' requires that the opening `{' of an action associated with a +rule begin on the same line as does the rule. You need instead to +write your rules as follows: + + + ^(foo|bar) { // CORRECT! + + } + + +File: flex.info, Node: How can I have multiple input sources feed into the same scanner at the same time?, Next: Can I build nested parsers that work with the same input file?, Prev: My actions are executing out of order or sometimes not at all., Up: FAQ + +How can I have multiple input sources feed into the same scanner at the same time? +================================================================================== + +If ... + * your scanner is free of backtracking (verified using `flex''s `-b' + flag), + + * AND you run your scanner interactively (`-I' option; default + unless using special table compression options), + + * AND you feed it one character at a time by redefining `YY_INPUT' + to do so, + + then every time it matches a token, it will have exhausted its input +buffer (because the scanner is free of backtracking). This means you +can safely use `select()' at the point and only call `yylex()' for +another token if `select()' indicates there's data available. + + That is, move the `select()' out from the input function to a point +where it determines whether `yylex()' gets called for the next token. + + With this approach, you will still have problems if your input can +arrive piecemeal; `select()' could inform you that the beginning of a +token is available, you call `yylex()' to get it, but it winds up +blocking waiting for the later characters in the token. + + Here's another way: Move your input multiplexing inside of +`YY_INPUT'. That is, whenever `YY_INPUT' is called, it `select()''s to +see where input is available. If input is available for the scanner, +it reads and returns the next byte. If input is available from another +source, it calls whatever function is responsible for reading from that +source. (If no input is available, it blocks until some input is +available.) I've used this technique in an interpreter I wrote that +both reads keyboard input using a `flex' scanner and IPC traffic from +sockets, and it works fine. + + +File: flex.info, Node: Can I build nested parsers that work with the same input file?, Next: How can I match text only at the end of a file?, Prev: How can I have multiple input sources feed into the same scanner at the same time?, Up: FAQ + +Can I build nested parsers that work with the same input file? +============================================================== + +This is not going to work without some additional effort. The reason is +that `flex' block-buffers the input it reads from `yyin'. This means +that the "outermost" `yylex()', when called, will automatically slurp +up the first 8K of input available on yyin, and subsequent calls to +other `yylex()''s won't see that input. You might be tempted to work +around this problem by redefining `YY_INPUT' to only return a small +amount of text, but it turns out that that approach is quite difficult. +Instead, the best solution is to combine all of your scanners into one +large scanner, using a different exclusive start condition for each. + + +File: flex.info, Node: How can I match text only at the end of a file?, Next: How can I make REJECT cascade across start condition boundaries?, Prev: Can I build nested parsers that work with the same input file?, Up: FAQ + +How can I match text only at the end of a file? +=============================================== + +There is no way to write a rule which is "match this text, but only if +it comes at the end of the file". You can fake it, though, if you +happen to have a character lying around that you don't allow in your +input. Then you redefine `YY_INPUT' to call your own routine which, if +it sees an `EOF', returns the magic character first (and remembers to +return a real `EOF' next time it's called). Then you could write: + + + <COMMENT>(.|\n)*{EOF_CHAR} /* saw comment at EOF */ + + +File: flex.info, Node: How can I make REJECT cascade across start condition boundaries?, Next: Why cant I use fast or full tables with interactive mode?, Prev: How can I match text only at the end of a file?, Up: FAQ + +How can I make REJECT cascade across start condition boundaries? +================================================================ + +You can do this as follows. Suppose you have a start condition `A', and +after exhausting all of the possible matches in `<A>', you want to try +matches in `<INITIAL>'. Then you could use the following: + + + %x A + %% + <A>rule_that_is_long ...; REJECT; + <A>rule ...; REJECT; /* shorter rule */ + <A>etc. + ... + <A>.|\n { + /* Shortest and last rule in <A>, so + * cascaded REJECTs will eventually + * wind up matching this rule. We want + * to now switch to the initial state + * and try matching from there instead. + */ + yyless(0); /* put back matched text */ + BEGIN(INITIAL); + } + + +File: flex.info, Node: Why cant I use fast or full tables with interactive mode?, Next: How much faster is -F or -f than -C?, Prev: How can I make REJECT cascade across start condition boundaries?, Up: FAQ + +Why can't I use fast or full tables with interactive mode? +========================================================== + +One of the assumptions flex makes is that interactive applications are +inherently slow (they're waiting on a human after all). It has to do +with how the scanner detects that it must be finished scanning a token. +For interactive scanners, after scanning each character the current +state is looked up in a table (essentially) to see whether there's a +chance of another input character possibly extending the length of the +match. If not, the scanner halts. For non-interactive scanners, the +end-of-token test is much simpler, basically a compare with 0, so no +memory bus cycles. Since the test occurs in the innermost scanning +loop, one would like to make it go as fast as possible. + + Still, it seems reasonable to allow the user to choose to trade off +a bit of performance in this area to gain the corresponding +flexibility. There might be another reason, though, why fast scanners +don't support the interactive option. + + +File: flex.info, Node: How much faster is -F or -f than -C?, Next: If I have a simple grammar cant I just parse it with flex?, Prev: Why cant I use fast or full tables with interactive mode?, Up: FAQ + +How much faster is -F or -f than -C? +==================================== + +Much faster (factor of 2-3). + + +File: flex.info, Node: If I have a simple grammar cant I just parse it with flex?, Next: Why doesn't yyrestart() set the start state back to INITIAL?, Prev: How much faster is -F or -f than -C?, Up: FAQ + +If I have a simple grammar can't I just parse it with flex? +=========================================================== + +Is your grammar recursive? That's almost always a sign that you're +better off using a parser/scanner rather than just trying to use a +scanner alone. + + +File: flex.info, Node: Why doesn't yyrestart() set the start state back to INITIAL?, Next: How can I match C-style comments?, Prev: If I have a simple grammar cant I just parse it with flex?, Up: FAQ + +Why doesn't yyrestart() set the start state back to INITIAL? +============================================================ + +There are two reasons. The first is that there might be programs that +rely on the start state not changing across file changes. The second +is that beginning with `flex' version 2.4, use of `yyrestart()' is no +longer required, so fixing the problem there doesn't solve the more +general problem. + + +File: flex.info, Node: How can I match C-style comments?, Next: The period isn't working the way I expected., Prev: Why doesn't yyrestart() set the start state back to INITIAL?, Up: FAQ + +How can I match C-style comments? +================================= + +You might be tempted to try something like this: + + + "/*".*"*/" // WRONG! + + or, worse, this: + + + "/*"(.|\n)"*/" // WRONG! + + The above rules will eat too much input, and blow up on things like: + + + /* a comment */ do_my_thing( "oops */" ); + + Here is one way which allows you to track line information: + + + <INITIAL>{ + "/*" BEGIN(IN_COMMENT); + } + <IN_COMMENT>{ + "*/" BEGIN(INITIAL); + [^*\n]+ // eat comment in chunks + "*" // eat the lone star + \n yylineno++; + } + + +File: flex.info, Node: The period isn't working the way I expected., Next: Can I get the flex manual in another format?, Prev: How can I match C-style comments?, Up: FAQ + +The '.' isn't working the way I expected. +========================================= + +Here are some tips for using `.': + + * A common mistake is to place the grouping parenthesis AFTER an + operator, when you really meant to place the parenthesis BEFORE + the operator, e.g., you probably want this `(foo|bar)+' and NOT + this `(foo|bar+)'. + + The first pattern matches the words `foo' or `bar' any number of + times, e.g., it matches the text `barfoofoobarfoo'. The second + pattern matches a single instance of `foo' or a single instance of + `bar' followed by one or more `r's, e.g., it matches the text + `barrrr' . + + * A `.' inside `[]''s just means a literal`.' (period), and NOT "any + character except newline". + + * Remember that `.' matches any character EXCEPT `\n' (and `EOF'). + If you really want to match ANY character, including newlines, + then use `(.|\n)' Beware that the regex `(.|\n)+' will match your + entire input! + + * Finally, if you want to match a literal `.' (a period), then use + `[.]' or `"."' + + +File: flex.info, Node: Can I get the flex manual in another format?, Next: Does there exist a "faster" NDFA->DFA algorithm?, Prev: The period isn't working the way I expected., Up: FAQ + +Can I get the flex manual in another format? +============================================ + +The `flex' source distribution includes a texinfo manual. You are free +to convert that texinfo into whatever format you desire. The `texinfo' +package includes tools for conversion to a number of formats. + + +File: flex.info, Node: Does there exist a "faster" NDFA->DFA algorithm?, Next: How does flex compile the DFA so quickly?, Prev: Can I get the flex manual in another format?, Up: FAQ + +Does there exist a "faster" NDFA->DFA algorithm? +================================================ + +There's no way around the potential exponential running time - it can +take you exponential time just to enumerate all of the DFA states. In +practice, though, the running time is closer to linear, or sometimes +quadratic. + + +File: flex.info, Node: How does flex compile the DFA so quickly?, Next: How can I use more than 8192 rules?, Prev: Does there exist a "faster" NDFA->DFA algorithm?, Up: FAQ + +How does flex compile the DFA so quickly? +========================================= + +There are two big speed wins that `flex' uses: + + 1. It analyzes the input rules to construct equivalence classes for + those characters that always make the same transitions. It then + rewrites the NFA using equivalence classes for transitions instead + of characters. This cuts down the NFA->DFA computation time + dramatically, to the point where, for uncompressed DFA tables, the + DFA generation is often I/O bound in writing out the tables. + + 2. It maintains hash values for previously computed DFA states, so + testing whether a newly constructed DFA state is equivalent to a + previously constructed state can be done very quickly, by first + comparing hash values. + + +File: flex.info, Node: How can I use more than 8192 rules?, Next: How do I abandon a file in the middle of a scan and switch to a new file?, Prev: How does flex compile the DFA so quickly?, Up: FAQ + +How can I use more than 8192 rules? +=================================== + +`Flex' is compiled with an upper limit of 8192 rules per scanner. If +you need more than 8192 rules in your scanner, you'll have to recompile +`flex' with the following changes in `flexdef.h': + + + < #define YY_TRAILING_MASK 0x2000 + < #define YY_TRAILING_HEAD_MASK 0x4000 + -- + > #define YY_TRAILING_MASK 0x20000000 + > #define YY_TRAILING_HEAD_MASK 0x40000000 + + This should work okay as long as your C compiler uses 32 bit +integers. But you might want to think about whether using such a huge +number of rules is the best way to solve your problem. + + The following may also be relevant: + + With luck, you should be able to increase the definitions in +flexdef.h for: + + + #define JAMSTATE -32766 /* marks a reference to the state that always jams */ + #define MAXIMUM_MNS 31999 + #define BAD_SUBSCRIPT -32767 + + recompile everything, and it'll all work. Flex only has these +16-bit-like values built into it because a long time ago it was +developed on a machine with 16-bit ints. I've given this advice to +others in the past but haven't heard back from them whether it worked +okay or not... + + +File: flex.info, Node: How do I abandon a file in the middle of a scan and switch to a new file?, Next: How do I execute code only during initialization (only before the first scan)?, Prev: How can I use more than 8192 rules?, Up: FAQ + +How do I abandon a file in the middle of a scan and switch to a new file? +========================================================================= + +Just call `yyrestart(newfile)'. Be sure to reset the start state if you +want a "fresh start, since `yyrestart' does NOT reset the start state +back to `INITIAL'. + + +File: flex.info, Node: How do I execute code only during initialization (only before the first scan)?, Next: How do I execute code at termination?, Prev: How do I abandon a file in the middle of a scan and switch to a new file?, Up: FAQ + +How do I execute code only during initialization (only before the first scan)? +============================================================================== + +You can specify an initial action by defining the macro `YY_USER_INIT' +(though note that `yyout' may not be available at the time this macro +is executed). Or you can add to the beginning of your rules section: + + + %% + /* Must be indented! */ + static int did_init = 0; + + if ( ! did_init ){ + do_my_init(); + did_init = 1; + } + + +File: flex.info, Node: How do I execute code at termination?, Next: Where else can I find help?, Prev: How do I execute code only during initialization (only before the first scan)?, Up: FAQ + +How do I execute code at termination? +===================================== + +You can specify an action for the `<<EOF>>' rule. + + +File: flex.info, Node: Where else can I find help?, Next: Can I include comments in the "rules" section of the file?, Prev: How do I execute code at termination?, Up: FAQ + +Where else can I find help? +=========================== + +You can find the flex homepage on the web at +`http://flex.sourceforge.net/'. See that page for details about flex +mailing lists as well. + + +File: flex.info, Node: Can I include comments in the "rules" section of the file?, Next: I get an error about undefined yywrap()., Prev: Where else can I find help?, Up: FAQ + +Can I include comments in the "rules" section of the file? +========================================================== + +Yes, just about anywhere you want to. See the manual for the specific +syntax. + + +File: flex.info, Node: I get an error about undefined yywrap()., Next: How can I change the matching pattern at run time?, Prev: Can I include comments in the "rules" section of the file?, Up: FAQ + +I get an error about undefined yywrap(). +======================================== + +You must supply a `yywrap()' function of your own, or link to `libfl.a' +(which provides one), or use + + + %option noyywrap + + in your source to say you don't want a `yywrap()' function. + + +File: flex.info, Node: How can I change the matching pattern at run time?, Next: How can I expand macros in the input?, Prev: I get an error about undefined yywrap()., Up: FAQ + +How can I change the matching pattern at run time? +================================================== + +You can't, it's compiled into a static table when flex builds the +scanner. + + +File: flex.info, Node: How can I expand macros in the input?, Next: How can I build a two-pass scanner?, Prev: How can I change the matching pattern at run time?, Up: FAQ + +How can I expand macros in the input? +===================================== + +The best way to approach this problem is at a higher level, e.g., in +the parser. + + However, you can do this using multiple input buffers. + + + %% + macro/[a-z]+ { + /* Saw the macro "macro" followed by extra stuff. */ + main_buffer = YY_CURRENT_BUFFER; + expansion_buffer = yy_scan_string(expand(yytext)); + yy_switch_to_buffer(expansion_buffer); + } + + <<EOF>> { + if ( expansion_buffer ) + { + // We were doing an expansion, return to where + // we were. + yy_switch_to_buffer(main_buffer); + yy_delete_buffer(expansion_buffer); + expansion_buffer = 0; + } + else + yyterminate(); + } + + You probably will want a stack of expansion buffers to allow nested +macros. From the above though hopefully the idea is clear. + + +File: flex.info, Node: How can I build a two-pass scanner?, Next: How do I match any string not matched in the preceding rules?, Prev: How can I expand macros in the input?, Up: FAQ + +How can I build a two-pass scanner? +=================================== + +One way to do it is to filter the first pass to a temporary file, then +process the temporary file on the second pass. You will probably see a +performance hit, due to all the disk I/O. + + When you need to look ahead far forward like this, it almost always +means that the right solution is to build a parse tree of the entire +input, then walk it after the parse in order to generate the output. +In a sense, this is a two-pass approach, once through the text and once +through the parse tree, but the performance hit for the latter is +usually an order of magnitude smaller, since everything is already +classified, in binary format, and residing in memory. + + +File: flex.info, Node: How do I match any string not matched in the preceding rules?, Next: I am trying to port code from AT&T lex that uses yysptr and yysbuf., Prev: How can I build a two-pass scanner?, Up: FAQ + +How do I match any string not matched in the preceding rules? +============================================================= + +One way to assign precedence, is to place the more specific rules +first. If two rules would match the same input (same sequence of +characters) then the first rule listed in the `flex' input wins, e.g., + + + %% + foo[a-zA-Z_]+ return FOO_ID; + bar[a-zA-Z_]+ return BAR_ID; + [a-zA-Z_]+ return GENERIC_ID; + + Note that the rule `[a-zA-Z_]+' must come *after* the others. It +will match the same amount of text as the more specific rules, and in +that case the `flex' scanner will pick the first rule listed in your +scanner as the one to match. + + +File: flex.info, Node: I am trying to port code from AT&T lex that uses yysptr and yysbuf., Next: Is there a way to make flex treat NULL like a regular character?, Prev: How do I match any string not matched in the preceding rules?, Up: FAQ + +I am trying to port code from AT&T lex that uses yysptr and yysbuf. +=================================================================== + +Those are internal variables pointing into the AT&T scanner's input +buffer. I imagine they're being manipulated in user versions of the +`input()' and `unput()' functions. If so, what you need to do is +analyze those functions to figure out what they're doing, and then +replace `input()' with an appropriate definition of `YY_INPUT'. You +shouldn't need to (and must not) replace `flex''s `unput()' function. + + +File: flex.info, Node: Is there a way to make flex treat NULL like a regular character?, Next: Whenever flex can not match the input it says "flex scanner jammed"., Prev: I am trying to port code from AT&T lex that uses yysptr and yysbuf., Up: FAQ + +Is there a way to make flex treat NULL like a regular character? +================================================================ + +Yes, `\0' and `\x00' should both do the trick. Perhaps you have an +ancient version of `flex'. The latest release is version 2.5.34. + + +File: flex.info, Node: Whenever flex can not match the input it says "flex scanner jammed"., Next: Why doesn't flex have non-greedy operators like perl does?, Prev: Is there a way to make flex treat NULL like a regular character?, Up: FAQ + +Whenever flex can not match the input it says "flex scanner jammed". +==================================================================== + +You need to add a rule that matches the otherwise-unmatched text, e.g., + + + %option yylineno + %% + [[a bunch of rules here]] + + . printf("bad input character '%s' at line %d\n", yytext, yylineno); + + See `%option default' for more information. + + +File: flex.info, Node: Why doesn't flex have non-greedy operators like perl does?, Next: Memory leak - 16386 bytes allocated by malloc., Prev: Whenever flex can not match the input it says "flex scanner jammed"., Up: FAQ + +Why doesn't flex have non-greedy operators like perl does? +========================================================== + +A DFA can do a non-greedy match by stopping the first time it enters an +accepting state, instead of consuming input until it determines that no +further matching is possible (a "jam" state). This is actually easier +to implement than longest leftmost match (which flex does). + + But it's also much less useful than longest leftmost match. In +general, when you find yourself wishing for non-greedy matching, that's +usually a sign that you're trying to make the scanner do some parsing. +That's generally the wrong approach, since it lacks the power to do a +decent job. Better is to either introduce a separate parser, or to +split the scanner into multiple scanners using (exclusive) start +conditions. + + You might have a separate start state once you've seen the `BEGIN'. +In that state, you might then have a regex that will match `END' (to +kick you out of the state), and perhaps `(.|\n)' to get a single +character within the chunk ... + + This approach also has much better error-reporting properties. + + +File: flex.info, Node: Memory leak - 16386 bytes allocated by malloc., Next: How do I track the byte offset for lseek()?, Prev: Why doesn't flex have non-greedy operators like perl does?, Up: FAQ + +Memory leak - 16386 bytes allocated by malloc. +============================================== + +UPDATED 2002-07-10: As of `flex' version 2.5.9, this leak means that +you did not call `yylex_destroy()'. If you are using an earlier version +of `flex', then read on. + + The leak is about 16426 bytes. That is, (8192 * 2 + 2) for the +read-buffer, and about 40 for `struct yy_buffer_state' (depending upon +alignment). The leak is in the non-reentrant C scanner only (NOT in the +reentrant scanner, NOT in the C++ scanner). Since `flex' doesn't know +when you are done, the buffer is never freed. + + However, the leak won't multiply since the buffer is reused no +matter how many times you call `yylex()'. + + If you want to reclaim the memory when you are completely done +scanning, then you might try this: + + + /* For non-reentrant C scanner only. */ + yy_delete_buffer(YY_CURRENT_BUFFER); + yy_init = 1; + + Note: `yy_init' is an "internal variable", and hasn't been tested in +this situation. It is possible that some other globals may need +resetting as well. + + +File: flex.info, Node: How do I track the byte offset for lseek()?, Next: How do I use my own I/O classes in a C++ scanner?, Prev: Memory leak - 16386 bytes allocated by malloc., Up: FAQ + +How do I track the byte offset for lseek()? +=========================================== + + + > We thought that it would be possible to have this number through the + > evaluation of the following expression: + > + > seek_position = (no_buffers)*YY_READ_BUF_SIZE + yy_c_buf_p - YY_CURRENT_BUFFER->yy_ch_buf + + While this is the right idea, it has two problems. The first is that +it's possible that `flex' will request less than `YY_READ_BUF_SIZE' +during an invocation of `YY_INPUT' (or that your input source will +return less even though `YY_READ_BUF_SIZE' bytes were requested). The +second problem is that when refilling its internal buffer, `flex' keeps +some characters from the previous buffer (because usually it's in the +middle of a match, and needs those characters to construct `yytext' for +the match once it's done). Because of this, `yy_c_buf_p - +YY_CURRENT_BUFFER->yy_ch_buf' won't be exactly the number of characters +already read from the current buffer. + + An alternative solution is to count the number of characters you've +matched since starting to scan. This can be done by using +`YY_USER_ACTION'. For example, + + + #define YY_USER_ACTION num_chars += yyleng; + + (You need to be careful to update your bookkeeping if you use +`yymore('), `yyless()', `unput()', or `input()'.) + + +File: flex.info, Node: How do I use my own I/O classes in a C++ scanner?, Next: How do I skip as many chars as possible?, Prev: How do I track the byte offset for lseek()?, Up: FAQ + +How do I use my own I/O classes in a C++ scanner? +================================================= + +When the flex C++ scanning class rewrite finally happens, then this +sort of thing should become much easier. + + You can do this by passing the various functions (such as +`LexerInput()' and `LexerOutput()') NULL `iostream*''s, and then +dealing with your own I/O classes surreptitiously (i.e., stashing them +in special member variables). This works because the only assumption +about the lexer regarding what's done with the iostream's is that +they're ultimately passed to `LexerInput()' and `LexerOutput', which +then do whatever is necessary with them. + + +File: flex.info, Node: How do I skip as many chars as possible?, Next: deleteme00, Prev: How do I use my own I/O classes in a C++ scanner?, Up: FAQ + +How do I skip as many chars as possible? +======================================== + +How do I skip as many chars as possible - without interfering with the +other patterns? + + In the example below, we want to skip over characters until we see +the phrase "endskip". The following will _NOT_ work correctly (do you +see why not?) + + + /* INCORRECT SCANNER */ + %x SKIP + %% + <INITIAL>startskip BEGIN(SKIP); + ... + <SKIP>"endskip" BEGIN(INITIAL); + <SKIP>.* ; + + The problem is that the pattern .* will eat up the word "endskip." +The simplest (but slow) fix is: + + + <SKIP>"endskip" BEGIN(INITIAL); + <SKIP>. ; + + The fix involves making the second rule match more, without making +it match "endskip" plus something else. So for example: + + + <SKIP>"endskip" BEGIN(INITIAL); + <SKIP>[^e]+ ; + <SKIP>. ;/* so you eat up e's, too */ + + +File: flex.info, Node: deleteme00, Next: Are certain equivalent patterns faster than others?, Prev: How do I skip as many chars as possible?, Up: FAQ + +deleteme00 +========== + + + QUESTION: + When was flex born? + + Vern Paxson took over + the Software Tools lex project from Jef Poskanzer in 1982. At that point it + was written in Ratfor. Around 1987 or so, Paxson translated it into C, and + a legend was born :-). + + +File: flex.info, Node: Are certain equivalent patterns faster than others?, Next: Is backing up a big deal?, Prev: deleteme00, Up: FAQ + +Are certain equivalent patterns faster than others? +=================================================== + + + To: Adoram Rogel <adoram@orna.hybridge.com> + Subject: Re: Flex 2.5.2 performance questions + In-reply-to: Your message of Wed, 18 Sep 96 11:12:17 EDT. + Date: Wed, 18 Sep 96 10:51:02 PDT + From: Vern Paxson <vern> + + [Note, the most recent flex release is 2.5.4, which you can get from + ftp.ee.lbl.gov. It has bug fixes over 2.5.2 and 2.5.3.] + + > 1. Using the pattern + > ([Ff](oot)?)?[Nn](ote)?(\.)? + > instead of + > (((F|f)oot(N|n)ote)|((N|n)ote)|((N|n)\.)|((F|f)(N|n)(\.))) + > (in a very complicated flex program) caused the program to slow from + > 300K+/min to 100K/min (no other changes were done). + + These two are not equivalent. For example, the first can match "footnote." + but the second can only match "footnote". This is almost certainly the + cause in the discrepancy - the slower scanner run is matching more tokens, + and/or having to do more backing up. + + > 2. Which of these two are better: [Ff]oot or (F|f)oot ? + + From a performance point of view, they're equivalent (modulo presumably + minor effects such as memory cache hit rates; and the presence of trailing + context, see below). From a space point of view, the first is slightly + preferable. + + > 3. I have a pattern that look like this: + > pats {p1}|{p2}|{p3}|...|{p50} (50 patterns ORd) + > + > running yet another complicated program that includes the following rule: + > <snext>{and}/{no4}{bb}{pats} + > + > gets me to "too complicated - over 32,000 states"... + + I can't tell from this example whether the trailing context is variable-length + or fixed-length (it could be the latter if {and} is fixed-length). If it's + variable length, which flex -p will tell you, then this reflects a basic + performance problem, and if you can eliminate it by restructuring your + scanner, you will see significant improvement. + + > so I divided {pats} to {pats1}, {pats2},..., {pats5} each consists of about + > 10 patterns and changed the rule to be 5 rules. + > This did compile, but what is the rule of thumb here ? + + The rule is to avoid trailing context other than fixed-length, in which for + a/b, either the 'a' pattern or the 'b' pattern have a fixed length. Use + of the '|' operator automatically makes the pattern variable length, so in + this case '[Ff]oot' is preferred to '(F|f)oot'. + + > 4. I changed a rule that looked like this: + > <snext8>{and}{bb}/{ROMAN}[^A-Za-z] { BEGIN... + > + > to the next 2 rules: + > <snext8>{and}{bb}/{ROMAN}[A-Za-z] { ECHO;} + > <snext8>{and}{bb}/{ROMAN} { BEGIN... + > + > Again, I understand the using [^...] will cause a great performance loss + + Actually, it doesn't cause any sort of performance loss. It's a surprising + fact about regular expressions that they always match in linear time + regardless of how complex they are. + + > but are there any specific rules about it ? + + See the "Performance Considerations" section of the man page, and also + the example in MISC/fastwc/. + + Vern + + +File: flex.info, Node: Is backing up a big deal?, Next: Can I fake multi-byte character support?, Prev: Are certain equivalent patterns faster than others?, Up: FAQ + +Is backing up a big deal? +========================= + + + To: Adoram Rogel <adoram@hybridge.com> + Subject: Re: Flex 2.5.2 performance questions + In-reply-to: Your message of Thu, 19 Sep 96 10:16:04 EDT. + Date: Thu, 19 Sep 96 09:58:00 PDT + From: Vern Paxson <vern> + + > a lot about the backing up problem. + > I believe that there lies my biggest problem, and I'll try to improve + > it. + + Since you have variable trailing context, this is a bigger performance + problem. Fixing it is usually easier than fixing backing up, which in a + complicated scanner (yours seems to fit the bill) can be extremely + difficult to do correctly. + + You also don't mention what flags you are using for your scanner. + -f makes a large speed difference, and -Cfe buys you nearly as much + speed but the resulting scanner is considerably smaller. + + > I have an | operator in {and} and in {pats} so both of them are variable + > length. + + -p should have reported this. + + > Is changing one of them to fixed-length is enough ? + + Yes. + + > Is it possible to change the 32,000 states limit ? + + Yes. I've appended instructions on how. Before you make this change, + though, you should think about whether there are ways to fundamentally + simplify your scanner - those are certainly preferable! + + Vern + + To increase the 32K limit (on a machine with 32 bit integers), you increase + the magnitude of the following in flexdef.h: + + #define JAMSTATE -32766 /* marks a reference to the state that always jams */ + #define MAXIMUM_MNS 31999 + #define BAD_SUBSCRIPT -32767 + #define MAX_SHORT 32700 + + Adding a 0 or two after each should do the trick. + + +File: flex.info, Node: Can I fake multi-byte character support?, Next: deleteme01, Prev: Is backing up a big deal?, Up: FAQ + +Can I fake multi-byte character support? +======================================== + + + To: Heeman_Lee@hp.com + Subject: Re: flex - multi-byte support? + In-reply-to: Your message of Thu, 03 Oct 1996 17:24:04 PDT. + Date: Fri, 04 Oct 1996 11:42:18 PDT + From: Vern Paxson <vern> + + > I assume as long as my *.l file defines the + > range of expected character code values (in octal format), flex will + > scan the file and read multi-byte characters correctly. But I have no + > confidence in this assumption. + + Your lack of confidence is justified - this won't work. + + Flex has in it a widespread assumption that the input is processed + one byte at a time. Fixing this is on the to-do list, but is involved, + so it won't happen any time soon. In the interim, the best I can suggest + (unless you want to try fixing it yourself) is to write your rules in + terms of pairs of bytes, using definitions in the first section: + + X \xfe\xc2 + ... + %% + foo{X}bar found_foo_fe_c2_bar(); + + etc. Definitely a pain - sorry about that. + + By the way, the email address you used for me is ancient, indicating you + have a very old version of flex. You can get the most recent, 2.5.4, from + ftp.ee.lbl.gov. + + Vern + + +File: flex.info, Node: deleteme01, Next: Can you discuss some flex internals?, Prev: Can I fake multi-byte character support?, Up: FAQ + +deleteme01 +========== + + + To: moleary@primus.com + Subject: Re: Flex / Unicode compatibility question + In-reply-to: Your message of Tue, 22 Oct 1996 10:15:42 PDT. + Date: Tue, 22 Oct 1996 11:06:13 PDT + From: Vern Paxson <vern> + + Unfortunately flex at the moment has a widespread assumption within it + that characters are processed 8 bits at a time. I don't see any easy + fix for this (other than writing your rules in terms of double characters - + a pain). I also don't know of a wider lex, though you might try surfing + the Plan 9 stuff because I know it's a Unicode system, and also the PCCT + toolkit (try searching say Alta Vista for "Purdue Compiler Construction + Toolkit"). + + Fixing flex to handle wider characters is on the long-term to-do list. + But since flex is a strictly spare-time project these days, this probably + won't happen for quite a while, unless someone else does it first. + + Vern + + +File: flex.info, Node: Can you discuss some flex internals?, Next: unput() messes up yy_at_bol, Prev: deleteme01, Up: FAQ + +Can you discuss some flex internals? +==================================== + + + To: Johan Linde <jl@theophys.kth.se> + Subject: Re: translation of flex + In-reply-to: Your message of Sun, 10 Nov 1996 09:16:36 PST. + Date: Mon, 11 Nov 1996 10:33:50 PST + From: Vern Paxson <vern> + + > I'm working for the Swedish team translating GNU program, and I'm currently + > working with flex. I have a few questions about some of the messages which + > I hope you can answer. + + All of the things you're wondering about, by the way, concerning flex + internals - probably the only person who understands what they mean in + English is me! So I wouldn't worry too much about getting them right. + That said ... + + > #: main.c:545 + > msgid " %d protos created\n" + > + > Does proto mean prototype? + + Yes - prototypes of state compression tables. + + > #: main.c:539 + > msgid " %d/%d (peak %d) template nxt-chk entries created\n" + > + > Here I'm mainly puzzled by 'nxt-chk'. I guess it means 'next-check'. (?) + > However, 'template next-check entries' doesn't make much sense to me. To be + > able to find a good translation I need to know a little bit more about it. + + There is a scheme in the Aho/Sethi/Ullman compiler book for compressing + scanner tables. It involves creating two pairs of tables. The first has + "base" and "default" entries, the second has "next" and "check" entries. + The "base" entry is indexed by the current state and yields an index into + the next/check table. The "default" entry gives what to do if the state + transition isn't found in next/check. The "next" entry gives the next + state to enter, but only if the "check" entry verifies that this entry is + correct for the current state. Flex creates templates of series of + next/check entries and then encodes differences from these templates as a + way to compress the tables. + + > #: main.c:533 + > msgid " %d/%d base-def entries created\n" + > + > The same problem here for 'base-def'. + + See above. + + Vern + + +File: flex.info, Node: unput() messes up yy_at_bol, Next: The | operator is not doing what I want, Prev: Can you discuss some flex internals?, Up: FAQ + +unput() messes up yy_at_bol +=========================== + + + To: Xinying Li <xli@npac.syr.edu> + Subject: Re: FLEX ? + In-reply-to: Your message of Wed, 13 Nov 1996 17:28:38 PST. + Date: Wed, 13 Nov 1996 19:51:54 PST + From: Vern Paxson <vern> + + > "unput()" them to input flow, question occurs. If I do this after I scan + > a carriage, the variable "YY_CURRENT_BUFFER->yy_at_bol" is changed. That + > means the carriage flag has gone. + + You can control this by calling yy_set_bol(). It's described in the manual. + + > And if in pre-reading it goes to the end of file, is anything done + > to control the end of curren buffer and end of file? + + No, there's no way to put back an end-of-file. + + > By the way I am using flex 2.5.2 and using the "-l". + + The latest release is 2.5.4, by the way. It fixes some bugs in 2.5.2 and + 2.5.3. You can get it from ftp.ee.lbl.gov. + + Vern + + +File: flex.info, Node: The | operator is not doing what I want, Next: Why can't flex understand this variable trailing context pattern?, Prev: unput() messes up yy_at_bol, Up: FAQ + +The | operator is not doing what I want +======================================= + + + To: Alain.ISSARD@st.com + Subject: Re: Start condition with FLEX + In-reply-to: Your message of Mon, 18 Nov 1996 09:45:02 PST. + Date: Mon, 18 Nov 1996 10:41:34 PST + From: Vern Paxson <vern> + + > I am not able to use the start condition scope and to use the | (OR) with + > rules having start conditions. + + The problem is that if you use '|' as a regular expression operator, for + example "a|b" meaning "match either 'a' or 'b'", then it must *not* have + any blanks around it. If you instead want the special '|' *action* (which + from your scanner appears to be the case), which is a way of giving two + different rules the same action: + + foo | + bar matched_foo_or_bar(); + + then '|' *must* be separated from the first rule by whitespace and *must* + be followed by a new line. You *cannot* write it as: + + foo | bar matched_foo_or_bar(); + + even though you might think you could because yacc supports this syntax. + The reason for this unfortunately incompatibility is historical, but it's + unlikely to be changed. + + Your problems with start condition scope are simply due to syntax errors + from your use of '|' later confusing flex. + + Let me know if you still have problems. + + Vern + + +File: flex.info, Node: Why can't flex understand this variable trailing context pattern?, Next: The ^ operator isn't working, Prev: The | operator is not doing what I want, Up: FAQ + +Why can't flex understand this variable trailing context pattern? +================================================================= + + + To: Gregory Margo <gmargo@newton.vip.best.com> + Subject: Re: flex-2.5.3 bug report + In-reply-to: Your message of Sat, 23 Nov 1996 16:50:09 PST. + Date: Sat, 23 Nov 1996 17:07:32 PST + From: Vern Paxson <vern> + + > Enclosed is a lex file that "real" lex will process, but I cannot get + > flex to process it. Could you try it and maybe point me in the right direction? + + Your problem is that some of the definitions in the scanner use the '/' + trailing context operator, and have it enclosed in ()'s. Flex does not + allow this operator to be enclosed in ()'s because doing so allows undefined + regular expressions such as "(a/b)+". So the solution is to remove the + parentheses. Note that you must also be building the scanner with the -l + option for AT&T lex compatibility. Without this option, flex automatically + encloses the definitions in parentheses. + + Vern + + +File: flex.info, Node: The ^ operator isn't working, Next: Trailing context is getting confused with trailing optional patterns, Prev: Why can't flex understand this variable trailing context pattern?, Up: FAQ + +The ^ operator isn't working +============================ + + + To: Thomas Hadig <hadig@toots.physik.rwth-aachen.de> + Subject: Re: Flex Bug ? + In-reply-to: Your message of Tue, 26 Nov 1996 14:35:01 PST. + Date: Tue, 26 Nov 1996 11:15:05 PST + From: Vern Paxson <vern> + + > In my lexer code, i have the line : + > ^\*.* { } + > + > Thus all lines starting with an astrix (*) are comment lines. + > This does not work ! + + I can't get this problem to reproduce - it works fine for me. Note + though that if what you have is slightly different: + + COMMENT ^\*.* + %% + {COMMENT} { } + + then it won't work, because flex pushes back macro definitions enclosed + in ()'s, so the rule becomes + + (^\*.*) { } + + and now that the '^' operator is not at the immediate beginning of the + line, it's interpreted as just a regular character. You can avoid this + behavior by using the "-l" lex-compatibility flag, or "%option lex-compat". + + Vern + + +File: flex.info, Node: Trailing context is getting confused with trailing optional patterns, Next: Is flex GNU or not?, Prev: The ^ operator isn't working, Up: FAQ + +Trailing context is getting confused with trailing optional patterns +==================================================================== + + + To: Adoram Rogel <adoram@hybridge.com> + Subject: Re: Flex 2.5.4 BOF ??? + In-reply-to: Your message of Tue, 26 Nov 1996 16:10:41 PST. + Date: Wed, 27 Nov 1996 10:56:25 PST + From: Vern Paxson <vern> + + > Organization(s)?/[a-z] + > + > This matched "Organizations" (looking in debug mode, the trailing s + > was matched with trailing context instead of the optional (s) in the + > end of the word. + + That should only happen with lex. Flex can properly match this pattern. + (That might be what you're saying, I'm just not sure.) + + > Is there a way to avoid this dangerous trailing context problem ? + + Unfortunately, there's no easy way. On the other hand, I don't see why + it should be a problem. Lex's matching is clearly wrong, and I'd hope + that usually the intent remains the same as expressed with the pattern, + so flex's matching will be correct. + + Vern + + +File: flex.info, Node: Is flex GNU or not?, Next: ERASEME53, Prev: Trailing context is getting confused with trailing optional patterns, Up: FAQ + +Is flex GNU or not? +=================== + + + To: Cameron MacKinnon <mackin@interlog.com> + Subject: Re: Flex documentation bug + In-reply-to: Your message of Mon, 02 Dec 1996 00:07:08 PST. + Date: Sun, 01 Dec 1996 22:29:39 PST + From: Vern Paxson <vern> + + > I'm not sure how or where to submit bug reports (documentation or + > otherwise) for the GNU project stuff ... + + Well, strictly speaking flex isn't part of the GNU project. They just + distribute it because no one's written a decent GPL'd lex replacement. + So you should send bugs directly to me. Those sent to the GNU folks + sometimes find there way to me, but some may drop between the cracks. + + > In GNU Info, under the section 'Start Conditions', and also in the man + > page (mine's dated April '95) is a nice little snippet showing how to + > parse C quoted strings into a buffer, defined to be MAX_STR_CONST in + > size. Unfortunately, no overflow checking is ever done ... + + This is already mentioned in the manual: + + Finally, here's an example of how to match C-style quoted + strings using exclusive start conditions, including expanded + escape sequences (but not including checking for a string + that's too long): + + The reason for not doing the overflow checking is that it will needlessly + clutter up an example whose main purpose is just to demonstrate how to + use flex. + + The latest release is 2.5.4, by the way, available from ftp.ee.lbl.gov. + + Vern + + +File: flex.info, Node: ERASEME53, Next: I need to scan if-then-else blocks and while loops, Prev: Is flex GNU or not?, Up: FAQ + +ERASEME53 +========= + + + To: tsv@cs.UManitoba.CA + Subject: Re: Flex (reg).. + In-reply-to: Your message of Thu, 06 Mar 1997 23:50:16 PST. + Date: Thu, 06 Mar 1997 15:54:19 PST + From: Vern Paxson <vern> + + > [:alpha:] ([:alnum:] | \\_)* + + If your rule really has embedded blanks as shown above, then it won't + work, as the first blank delimits the rule from the action. (It wouldn't + even compile ...) You need instead: + + [:alpha:]([:alnum:]|\\_)* + + and that should work fine - there's no restriction on what can go inside + of ()'s except for the trailing context operator, '/'. + + Vern + + +File: flex.info, Node: I need to scan if-then-else blocks and while loops, Next: ERASEME55, Prev: ERASEME53, Up: FAQ + +I need to scan if-then-else blocks and while loops +================================================== + + + To: "Mike Stolnicki" <mstolnic@ford.com> + Subject: Re: FLEX help + In-reply-to: Your message of Fri, 30 May 1997 13:33:27 PDT. + Date: Fri, 30 May 1997 10:46:35 PDT + From: Vern Paxson <vern> + + > We'd like to add "if-then-else", "while", and "for" statements to our + > language ... + > We've investigated many possible solutions. The one solution that seems + > the most reasonable involves knowing the position of a TOKEN in yyin. + + I strongly advise you to instead build a parse tree (abstract syntax tree) + and loop over that instead. You'll find this has major benefits in keeping + your interpreter simple and extensible. + + That said, the functionality you mention for get_position and set_position + have been on the to-do list for a while. As flex is a purely spare-time + project for me, no guarantees when this will be added (in particular, it + for sure won't be for many months to come). + + Vern + + +File: flex.info, Node: ERASEME55, Next: ERASEME56, Prev: I need to scan if-then-else blocks and while loops, Up: FAQ + +ERASEME55 +========= + + + To: Colin Paul Adams <colin@colina.demon.co.uk> + Subject: Re: Flex C++ classes and Bison + In-reply-to: Your message of 09 Aug 1997 17:11:41 PDT. + Date: Fri, 15 Aug 1997 10:48:19 PDT + From: Vern Paxson <vern> + + > #define YY_DECL int yylex (YYSTYPE *lvalp, struct parser_control + > *parm) + > + > I have been trying to get this to work as a C++ scanner, but it does + > not appear to be possible (warning that it matches no declarations in + > yyFlexLexer, or something like that). + > + > Is this supposed to be possible, or is it being worked on (I DID + > notice the comment that scanner classes are still experimental, so I'm + > not too hopeful)? + + What you need to do is derive a subclass from yyFlexLexer that provides + the above yylex() method, squirrels away lvalp and parm into member + variables, and then invokes yyFlexLexer::yylex() to do the regular scanning. + + Vern + + +File: flex.info, Node: ERASEME56, Next: ERASEME57, Prev: ERASEME55, Up: FAQ + +ERASEME56 +========= + + + To: Mikael.Latvala@lmf.ericsson.se + Subject: Re: Possible mistake in Flex v2.5 document + In-reply-to: Your message of Fri, 05 Sep 1997 16:07:24 PDT. + Date: Fri, 05 Sep 1997 10:01:54 PDT + From: Vern Paxson <vern> + + > In that example you show how to count comment lines when using + > C style /* ... */ comments. My question is, shouldn't you take into + > account a scenario where end of a comment marker occurs inside + > character or string literals? + + The scanner certainly needs to also scan character and string literals. + However it does that (there's an example in the man page for strings), the + lexer will recognize the beginning of the literal before it runs across the + embedded "/*". Consequently, it will finish scanning the literal before it + even considers the possibility of matching "/*". + + Example: + + '([^']*|{ESCAPE_SEQUENCE})' + + will match all the text between the ''s (inclusive). So the lexer + considers this as a token beginning at the first ', and doesn't even + attempt to match other tokens inside it. + + I thinnk this subtlety is not worth putting in the manual, as I suspect + it would confuse more people than it would enlighten. + + Vern + + +File: flex.info, Node: ERASEME57, Next: Is there a repository for flex scanners?, Prev: ERASEME56, Up: FAQ + +ERASEME57 +========= + + + To: "Marty Leisner" <leisner@sdsp.mc.xerox.com> + Subject: Re: flex limitations + In-reply-to: Your message of Sat, 06 Sep 1997 11:27:21 PDT. + Date: Mon, 08 Sep 1997 11:38:08 PDT + From: Vern Paxson <vern> + + > %% + > [a-zA-Z]+ /* skip a line */ + > { printf("got %s\n", yytext); } + > %% + + What version of flex are you using? If I feed this to 2.5.4, it complains: + + "bug.l", line 5: EOF encountered inside an action + "bug.l", line 5: unrecognized rule + "bug.l", line 5: fatal parse error + + Not the world's greatest error message, but it manages to flag the problem. + + (With the introduction of start condition scopes, flex can't accommodate + an action on a separate line, since it's ambiguous with an indented rule.) + + You can get 2.5.4 from ftp.ee.lbl.gov. + + Vern + + +File: flex.info, Node: Is there a repository for flex scanners?, Next: How can I conditionally compile or preprocess my flex input file?, Prev: ERASEME57, Up: FAQ + +Is there a repository for flex scanners? +======================================== + +Not that we know of. You might try asking on comp.compilers. + + +File: flex.info, Node: How can I conditionally compile or preprocess my flex input file?, Next: Where can I find grammars for lex and yacc?, Prev: Is there a repository for flex scanners?, Up: FAQ + +How can I conditionally compile or preprocess my flex input file? +================================================================= + +Flex doesn't have a preprocessor like C does. You might try using m4, +or the C preprocessor plus a sed script to clean up the result. + + +File: flex.info, Node: Where can I find grammars for lex and yacc?, Next: I get an end-of-buffer message for each character scanned., Prev: How can I conditionally compile or preprocess my flex input file?, Up: FAQ + +Where can I find grammars for lex and yacc? +=========================================== + +In the sources for flex and bison. + + +File: flex.info, Node: I get an end-of-buffer message for each character scanned., Next: unnamed-faq-62, Prev: Where can I find grammars for lex and yacc?, Up: FAQ + +I get an end-of-buffer message for each character scanned. +========================================================== + +This will happen if your LexerInput() function returns only one +character at a time, which can happen either if you're scanner is +"interactive", or if the streams library on your platform always +returns 1 for yyin->gcount(). + + Solution: override LexerInput() with a version that returns whole +buffers. + + +File: flex.info, Node: unnamed-faq-62, Next: unnamed-faq-63, Prev: I get an end-of-buffer message for each character scanned., Up: FAQ + +unnamed-faq-62 +============== + + + To: Georg.Rehm@CL-KI.Uni-Osnabrueck.DE + Subject: Re: Flex maximums + In-reply-to: Your message of Mon, 17 Nov 1997 17:16:06 PST. + Date: Mon, 17 Nov 1997 17:16:15 PST + From: Vern Paxson <vern> + + > I took a quick look into the flex-sources and altered some #defines in + > flexdefs.h: + > + > #define INITIAL_MNS 64000 + > #define MNS_INCREMENT 1024000 + > #define MAXIMUM_MNS 64000 + + The things to fix are to add a couple of zeroes to: + + #define JAMSTATE -32766 /* marks a reference to the state that always jams */ + #define MAXIMUM_MNS 31999 + #define BAD_SUBSCRIPT -32767 + #define MAX_SHORT 32700 + + and, if you get complaints about too many rules, make the following change too: + + #define YY_TRAILING_MASK 0x200000 + #define YY_TRAILING_HEAD_MASK 0x400000 + + - Vern + + +File: flex.info, Node: unnamed-faq-63, Next: unnamed-faq-64, Prev: unnamed-faq-62, Up: FAQ + +unnamed-faq-63 +============== + + + To: jimmey@lexis-nexis.com (Jimmey Todd) + Subject: Re: FLEX question regarding istream vs ifstream + In-reply-to: Your message of Mon, 08 Dec 1997 15:54:15 PST. + Date: Mon, 15 Dec 1997 13:21:35 PST + From: Vern Paxson <vern> + + > stdin_handle = YY_CURRENT_BUFFER; + > ifstream fin( "aFile" ); + > yy_switch_to_buffer( yy_create_buffer( fin, YY_BUF_SIZE ) ); + > + > What I'm wanting to do, is pass the contents of a file thru one set + > of rules and then pass stdin thru another set... It works great if, I + > don't use the C++ classes. But since everything else that I'm doing is + > in C++, I thought I'd be consistent. + > + > The problem is that 'yy_create_buffer' is expecting an istream* as it's + > first argument (as stated in the man page). However, fin is a ifstream + > object. Any ideas on what I might be doing wrong? Any help would be + > appreciated. Thanks!! + + You need to pass &fin, to turn it into an ifstream* instead of an ifstream. + Then its type will be compatible with the expected istream*, because ifstream + is derived from istream. + + Vern + + +File: flex.info, Node: unnamed-faq-64, Next: unnamed-faq-65, Prev: unnamed-faq-63, Up: FAQ + +unnamed-faq-64 +============== + + + To: Enda Fadian <fadiane@piercom.ie> + Subject: Re: Question related to Flex man page? + In-reply-to: Your message of Tue, 16 Dec 1997 15:17:34 PST. + Date: Tue, 16 Dec 1997 14:17:09 PST + From: Vern Paxson <vern> + + > Can you explain to me what is ment by a long-jump in relation to flex? + + Using the longjmp() function while inside yylex() or a routine called by it. + + > what is the flex activation frame. + + Just yylex()'s stack frame. + + > As far as I can see yyrestart will bring me back to the sart of the input + > file and using flex++ isnot really an option! + + No, yyrestart() doesn't imply a rewind, even though its name might sound + like it does. It tells the scanner to flush its internal buffers and + start reading from the given file at its present location. + + Vern + + +File: flex.info, Node: unnamed-faq-65, Next: unnamed-faq-66, Prev: unnamed-faq-64, Up: FAQ + +unnamed-faq-65 +============== + + + To: hassan@larc.info.uqam.ca (Hassan Alaoui) + Subject: Re: Need urgent Help + In-reply-to: Your message of Sat, 20 Dec 1997 19:38:19 PST. + Date: Sun, 21 Dec 1997 21:30:46 PST + From: Vern Paxson <vern> + + > /usr/lib/yaccpar: In function `int yyparse()': + > /usr/lib/yaccpar:184: warning: implicit declaration of function `int yylex(...)' + > + > ld: Undefined symbol + > _yylex + > _yyparse + > _yyin + + This is a known problem with Solaris C++ (and/or Solaris yacc). I believe + the fix is to explicitly insert some 'extern "C"' statements for the + corresponding routines/symbols. + + Vern + + +File: flex.info, Node: unnamed-faq-66, Next: unnamed-faq-67, Prev: unnamed-faq-65, Up: FAQ + +unnamed-faq-66 +============== + + + To: mc0307@mclink.it + Cc: gnu@prep.ai.mit.edu + Subject: Re: [mc0307@mclink.it: Help request] + In-reply-to: Your message of Fri, 12 Dec 1997 17:57:29 PST. + Date: Sun, 21 Dec 1997 22:33:37 PST + From: Vern Paxson <vern> + + > This is my definition for float and integer types: + > . . . + > NZD [1-9] + > ... + > I've tested my program on other lex version (on UNIX Sun Solaris an HP + > UNIX) and it work well, so I think that my definitions are correct. + > There are any differences between Lex and Flex? + + There are indeed differences, as discussed in the man page. The one + you are probably running into is that when flex expands a name definition, + it puts parentheses around the expansion, while lex does not. There's + an example in the man page of how this can lead to different matching. + Flex's behavior complies with the POSIX standard (or at least with the + last POSIX draft I saw). + + Vern + + +File: flex.info, Node: unnamed-faq-67, Next: unnamed-faq-68, Prev: unnamed-faq-66, Up: FAQ + +unnamed-faq-67 +============== + + + To: hassan@larc.info.uqam.ca (Hassan Alaoui) + Subject: Re: Thanks + In-reply-to: Your message of Mon, 22 Dec 1997 16:06:35 PST. + Date: Mon, 22 Dec 1997 14:35:05 PST + From: Vern Paxson <vern> + + > Thank you very much for your help. I compile and link well with C++ while + > declaring 'yylex ...' extern, But a little problem remains. I get a + > segmentation default when executing ( I linked with lfl library) while it + > works well when using LEX instead of flex. Do you have some ideas about the + > reason for this ? + + The one possible reason for this that comes to mind is if you've defined + yytext as "extern char yytext[]" (which is what lex uses) instead of + "extern char *yytext" (which is what flex uses). If it's not that, then + I'm afraid I don't know what the problem might be. + + Vern + + +File: flex.info, Node: unnamed-faq-68, Next: unnamed-faq-69, Prev: unnamed-faq-67, Up: FAQ + +unnamed-faq-68 +============== + + + To: "Bart Niswonger" <NISWONGR@almaden.ibm.com> + Subject: Re: flex 2.5: c++ scanners & start conditions + In-reply-to: Your message of Tue, 06 Jan 1998 10:34:21 PST. + Date: Tue, 06 Jan 1998 19:19:30 PST + From: Vern Paxson <vern> + + > The problem is that when I do this (using %option c++) start + > conditions seem to not apply. + + The BEGIN macro modifies the yy_start variable. For C scanners, this + is a static with scope visible through the whole file. For C++ scanners, + it's a member variable, so it only has visible scope within a member + function. Your lexbegin() routine is not a member function when you + build a C++ scanner, so it's not modifying the correct yy_start. The + diagnostic that indicates this is that you found you needed to add + a declaration of yy_start in order to get your scanner to compile when + using C++; instead, the correct fix is to make lexbegin() a member + function (by deriving from yyFlexLexer). + + Vern + + +File: flex.info, Node: unnamed-faq-69, Next: unnamed-faq-70, Prev: unnamed-faq-68, Up: FAQ + +unnamed-faq-69 +============== + + + To: "Boris Zinin" <boris@ippe.rssi.ru> + Subject: Re: current position in flex buffer + In-reply-to: Your message of Mon, 12 Jan 1998 18:58:23 PST. + Date: Mon, 12 Jan 1998 12:03:15 PST + From: Vern Paxson <vern> + + > The problem is how to determine the current position in flex active + > buffer when a rule is matched.... + + You will need to keep track of this explicitly, such as by redefining + YY_USER_ACTION to count the number of characters matched. + + The latest flex release, by the way, is 2.5.4, available from ftp.ee.lbl.gov. + + Vern + + +File: flex.info, Node: unnamed-faq-70, Next: unnamed-faq-71, Prev: unnamed-faq-69, Up: FAQ + +unnamed-faq-70 +============== + + + To: Bik.Dhaliwal@bis.org + Subject: Re: Flex question + In-reply-to: Your message of Mon, 26 Jan 1998 13:05:35 PST. + Date: Tue, 27 Jan 1998 22:41:52 PST + From: Vern Paxson <vern> + + > That requirement involves knowing + > the character position at which a particular token was matched + > in the lexer. + + The way you have to do this is by explicitly keeping track of where + you are in the file, by counting the number of characters scanned + for each token (available in yyleng). It may prove convenient to + do this by redefining YY_USER_ACTION, as described in the manual. + + Vern + + +File: flex.info, Node: unnamed-faq-71, Next: unnamed-faq-72, Prev: unnamed-faq-70, Up: FAQ + +unnamed-faq-71 +============== + + + To: Vladimir Alexiev <vladimir@cs.ualberta.ca> + Subject: Re: flex: how to control start condition from parser? + In-reply-to: Your message of Mon, 26 Jan 1998 05:50:16 PST. + Date: Tue, 27 Jan 1998 22:45:37 PST + From: Vern Paxson <vern> + + > It seems useful for the parser to be able to tell the lexer about such + > context dependencies, because then they don't have to be limited to + > local or sequential context. + + One way to do this is to have the parser call a stub routine that's + included in the scanner's .l file, and consequently that has access ot + BEGIN. The only ugliness is that the parser can't pass in the state + it wants, because those aren't visible - but if you don't have many + such states, then using a different set of names doesn't seem like + to much of a burden. + + While generating a .h file like you suggests is certainly cleaner, + flex development has come to a virtual stand-still :-(, so a workaround + like the above is much more pragmatic than waiting for a new feature. + + Vern + + +File: flex.info, Node: unnamed-faq-72, Next: unnamed-faq-73, Prev: unnamed-faq-71, Up: FAQ + +unnamed-faq-72 +============== + + + To: Barbara Denny <denny@3com.com> + Subject: Re: freebsd flex bug? + In-reply-to: Your message of Fri, 30 Jan 1998 12:00:43 PST. + Date: Fri, 30 Jan 1998 12:42:32 PST + From: Vern Paxson <vern> + + > lex.yy.c:1996: parse error before `=' + + This is the key, identifying this error. (It may help to pinpoint + it by using flex -L, so it doesn't generate #line directives in its + output.) I will bet you heavy money that you have a start condition + name that is also a variable name, or something like that; flex spits + out #define's for each start condition name, mapping them to a number, + so you can wind up with: + + %x foo + %% + ... + %% + void bar() + { + int foo = 3; + } + + and the penultimate will turn into "int 1 = 3" after C preprocessing, + since flex will put "#define foo 1" in the generated scanner. + + Vern + + +File: flex.info, Node: unnamed-faq-73, Next: unnamed-faq-74, Prev: unnamed-faq-72, Up: FAQ + +unnamed-faq-73 +============== + + + To: Maurice Petrie <mpetrie@infoscigroup.com> + Subject: Re: Lost flex .l file + In-reply-to: Your message of Mon, 02 Feb 1998 14:10:01 PST. + Date: Mon, 02 Feb 1998 11:15:12 PST + From: Vern Paxson <vern> + + > I am curious as to + > whether there is a simple way to backtrack from the generated source to + > reproduce the lost list of tokens we are searching on. + + In theory, it's straight-forward to go from the DFA representation + back to a regular-expression representation - the two are isomorphic. + In practice, a huge headache, because you have to unpack all the tables + back into a single DFA representation, and then write a program to munch + on that and translate it into an RE. + + Sorry for the less-than-happy news ... + + Vern + + +File: flex.info, Node: unnamed-faq-74, Next: unnamed-faq-75, Prev: unnamed-faq-73, Up: FAQ + +unnamed-faq-74 +============== + + + To: jimmey@lexis-nexis.com (Jimmey Todd) + Subject: Re: Flex performance question + In-reply-to: Your message of Thu, 19 Feb 1998 11:01:17 PST. + Date: Thu, 19 Feb 1998 08:48:51 PST + From: Vern Paxson <vern> + + > What I have found, is that the smaller the data chunk, the faster the + > program executes. This is the opposite of what I expected. Should this be + > happening this way? + + This is exactly what will happen if your input file has embedded NULs. + From the man page: + + A final note: flex is slow when matching NUL's, particularly + when a token contains multiple NUL's. It's best to write + rules which match short amounts of text if it's anticipated + that the text will often include NUL's. + + So that's the first thing to look for. + + Vern + + +File: flex.info, Node: unnamed-faq-75, Next: unnamed-faq-76, Prev: unnamed-faq-74, Up: FAQ + +unnamed-faq-75 +============== + + + To: jimmey@lexis-nexis.com (Jimmey Todd) + Subject: Re: Flex performance question + In-reply-to: Your message of Thu, 19 Feb 1998 11:01:17 PST. + Date: Thu, 19 Feb 1998 15:42:25 PST + From: Vern Paxson <vern> + + So there are several problems. + + First, to go fast, you want to match as much text as possible, which + your scanners don't in the case that what they're scanning is *not* + a <RN> tag. So you want a rule like: + + [^<]+ + + Second, C++ scanners are particularly slow if they're interactive, + which they are by default. Using -B speeds it up by a factor of 3-4 + on my workstation. + + Third, C++ scanners that use the istream interface are slow, because + of how poorly implemented istream's are. I built two versions of + the following scanner: + + %% + .*\n + .* + %% + + and the C version inhales a 2.5MB file on my workstation in 0.8 seconds. + The C++ istream version, using -B, takes 3.8 seconds. + + Vern + + +File: flex.info, Node: unnamed-faq-76, Next: unnamed-faq-77, Prev: unnamed-faq-75, Up: FAQ + +unnamed-faq-76 +============== + + + To: "Frescatore, David (CRD, TAD)" <frescatore@exc01crdge.crd.ge.com> + Subject: Re: FLEX 2.5 & THE YEAR 2000 + In-reply-to: Your message of Wed, 03 Jun 1998 11:26:22 PDT. + Date: Wed, 03 Jun 1998 10:22:26 PDT + From: Vern Paxson <vern> + + > I am researching the Y2K problem with General Electric R&D + > and need to know if there are any known issues concerning + > the above mentioned software and Y2K regardless of version. + + There shouldn't be, all it ever does with the date is ask the system + for it and then print it out. + + Vern + + +File: flex.info, Node: unnamed-faq-77, Next: unnamed-faq-78, Prev: unnamed-faq-76, Up: FAQ + +unnamed-faq-77 +============== + + + To: "Hans Dermot Doran" <htd@ibhdoran.com> + Subject: Re: flex problem + In-reply-to: Your message of Wed, 15 Jul 1998 21:30:13 PDT. + Date: Tue, 21 Jul 1998 14:23:34 PDT + From: Vern Paxson <vern> + + > To overcome this, I gets() the stdin into a string and lex the string. The + > string is lexed OK except that the end of string isn't lexed properly + > (yy_scan_string()), that is the lexer dosn't recognise the end of string. + + Flex doesn't contain mechanisms for recognizing buffer endpoints. But if + you use fgets instead (which you should anyway, to protect against buffer + overflows), then the final \n will be preserved in the string, and you can + scan that in order to find the end of the string. + + Vern + + +File: flex.info, Node: unnamed-faq-78, Next: unnamed-faq-79, Prev: unnamed-faq-77, Up: FAQ + +unnamed-faq-78 +============== + + + To: soumen@almaden.ibm.com + Subject: Re: Flex++ 2.5.3 instance member vs. static member + In-reply-to: Your message of Mon, 27 Jul 1998 02:10:04 PDT. + Date: Tue, 28 Jul 1998 01:10:34 PDT + From: Vern Paxson <vern> + + > %{ + > int mylineno = 0; + > %} + > ws [ \t]+ + > alpha [A-Za-z] + > dig [0-9] + > %% + > + > Now you'd expect mylineno to be a member of each instance of class + > yyFlexLexer, but is this the case? A look at the lex.yy.cc file seems to + > indicate otherwise; unless I am missing something the declaration of + > mylineno seems to be outside any class scope. + > + > How will this work if I want to run a multi-threaded application with each + > thread creating a FlexLexer instance? + + Derive your own subclass and make mylineno a member variable of it. + + Vern + + +File: flex.info, Node: unnamed-faq-79, Next: unnamed-faq-80, Prev: unnamed-faq-78, Up: FAQ + +unnamed-faq-79 +============== + + + To: Adoram Rogel <adoram@hybridge.com> + Subject: Re: More than 32K states change hangs + In-reply-to: Your message of Tue, 04 Aug 1998 16:55:39 PDT. + Date: Tue, 04 Aug 1998 22:28:45 PDT + From: Vern Paxson <vern> + + > Vern Paxson, + > + > I followed your advice, posted on Usenet bu you, and emailed to me + > personally by you, on how to overcome the 32K states limit. I'm running + > on Linux machines. + > I took the full source of version 2.5.4 and did the following changes in + > flexdef.h: + > #define JAMSTATE -327660 + > #define MAXIMUM_MNS 319990 + > #define BAD_SUBSCRIPT -327670 + > #define MAX_SHORT 327000 + > + > and compiled. + > All looked fine, including check and bigcheck, so I installed. + + Hmmm, you shouldn't increase MAX_SHORT, though looking through my email + archives I see that I did indeed recommend doing so. Try setting it back + to 32700; that should suffice that you no longer need -Ca. If it still + hangs, then the interesting question is - where? + + > Compiling the same hanged program with a out-of-the-box (RedHat 4.2 + > distribution of Linux) + > flex 2.5.4 binary works. + + Since Linux comes with source code, you should diff it against what + you have to see what problems they missed. + + > Should I always compile with the -Ca option now ? even short and simple + > filters ? + + No, definitely not. It's meant to be for those situations where you + absolutely must squeeze every last cycle out of your scanner. + + Vern + + +File: flex.info, Node: unnamed-faq-80, Next: unnamed-faq-81, Prev: unnamed-faq-79, Up: FAQ + +unnamed-faq-80 +============== + + + To: "Schmackpfeffer, Craig" <Craig.Schmackpfeffer@usa.xerox.com> + Subject: Re: flex output for static code portion + In-reply-to: Your message of Tue, 11 Aug 1998 11:55:30 PDT. + Date: Mon, 17 Aug 1998 23:57:42 PDT + From: Vern Paxson <vern> + + > I would like to use flex under the hood to generate a binary file + > containing the data structures that control the parse. + + This has been on the wish-list for a long time. In principle it's + straight-forward - you redirect mkdata() et al's I/O to another file, + and modify the skeleton to have a start-up function that slurps these + into dynamic arrays. The concerns are (1) the scanner generation code + is hairy and full of corner cases, so it's easy to get surprised when + going down this path :-( ; and (2) being careful about buffering so + that when the tables change you make sure the scanner starts in the + correct state and reading at the right point in the input file. + + > I was wondering if you know of anyone who has used flex in this way. + + I don't - but it seems like a reasonable project to undertake (unlike + numerous other flex tweaks :-). + + Vern + + +File: flex.info, Node: unnamed-faq-81, Next: unnamed-faq-82, Prev: unnamed-faq-80, Up: FAQ + +unnamed-faq-81 +============== + + + Received: from 131.173.17.11 (131.173.17.11 [131.173.17.11]) + by ee.lbl.gov (8.9.1/8.9.1) with ESMTP id AAA03838 + for <vern@ee.lbl.gov>; Thu, 20 Aug 1998 00:47:57 -0700 (PDT) + Received: from hal.cl-ki.uni-osnabrueck.de (hal.cl-ki.Uni-Osnabrueck.DE [131.173.141.2]) + by deimos.rz.uni-osnabrueck.de (8.8.7/8.8.8) with ESMTP id JAA34694 + for <vern@ee.lbl.gov>; Thu, 20 Aug 1998 09:47:55 +0200 + Received: (from georg@localhost) by hal.cl-ki.uni-osnabrueck.de (8.6.12/8.6.12) id JAA34834 for vern@ee.lbl.gov; Thu, 20 Aug 1998 09:47:54 +0200 + From: Georg Rehm <georg@hal.cl-ki.uni-osnabrueck.de> + Message-Id: <199808200747.JAA34834@hal.cl-ki.uni-osnabrueck.de> + Subject: "flex scanner push-back overflow" + To: vern@ee.lbl.gov + Date: Thu, 20 Aug 1998 09:47:54 +0200 (MEST) + Reply-To: Georg.Rehm@CL-KI.Uni-Osnabrueck.DE + X-NoJunk: Do NOT send commercial mail, spam or ads to this address! + X-URL: http://www.cl-ki.uni-osnabrueck.de/~georg/ + X-Mailer: ELM [version 2.4ME+ PL28 (25)] + MIME-Version: 1.0 + Content-Type: text/plain; charset=US-ASCII + Content-Transfer-Encoding: 7bit + + Hi Vern, + + Yesterday, I encountered a strange problem: I use the macro processor m4 + to include some lengthy lists into a .l file. Following is a flex macro + definition that causes some serious pain in my neck: + + AUTHOR ("A. Boucard / L. Boucard"|"A. Dastarac / M. Levent"|"A.Boucaud / L.Boucaud"|"Abderrahim Lamchichi"|"Achmat Dangor"|"Adeline Toullier"|"Adewale Maja-Pearce"|"Ahmed Ziri"|"Akram Ellyas"|"Alain Bihr"|"Alain Gresh"|"Alain Guillemoles"|"Alain Joxe"|"Alain Morice"|"Alain Renon"|"Alain Zecchini"|"Albert Memmi"|"Alberto Manguel"|"Alex De Waal"|"Alfonso Artico"| [...]) + + The complete list contains about 10kB. When I try to "flex" this file + (on a Solaris 2.6 machine, using a modified flex 2.5.4 (I only increased + some of the predefined values in flexdefs.h) I get the error: + + myflex/flex -8 sentag.tmp.l + flex scanner push-back overflow + + When I remove the slashes in the macro definition everything works fine. + As I understand it, the double quotes escape the slash-character so it + really means "/" and not "trailing context". Furthermore, I tried to + escape the slashes with backslashes, but with no use, the same error message + appeared when flexing the code. + + Do you have an idea what's going on here? + + Greetings from Germany, + Georg + -- + Georg Rehm georg@cl-ki.uni-osnabrueck.de + Institute for Semantic Information Processing, University of Osnabrueck, FRG + + +File: flex.info, Node: unnamed-faq-82, Next: unnamed-faq-83, Prev: unnamed-faq-81, Up: FAQ + +unnamed-faq-82 +============== + + + To: Georg.Rehm@CL-KI.Uni-Osnabrueck.DE + Subject: Re: "flex scanner push-back overflow" + In-reply-to: Your message of Thu, 20 Aug 1998 09:47:54 PDT. + Date: Thu, 20 Aug 1998 07:05:35 PDT + From: Vern Paxson <vern> + + > myflex/flex -8 sentag.tmp.l + > flex scanner push-back overflow + + Flex itself uses a flex scanner. That scanner is running out of buffer + space when it tries to unput() the humongous macro you've defined. When + you remove the '/'s, you make it small enough so that it fits in the buffer; + removing spaces would do the same thing. + + The fix is to either rethink how come you're using such a big macro and + perhaps there's another/better way to do it; or to rebuild flex's own + scan.c with a larger value for + + #define YY_BUF_SIZE 16384 + + - Vern + + +File: flex.info, Node: unnamed-faq-83, Next: unnamed-faq-84, Prev: unnamed-faq-82, Up: FAQ + +unnamed-faq-83 +============== + + + To: Jan Kort <jan@research.techforce.nl> + Subject: Re: Flex + In-reply-to: Your message of Fri, 04 Sep 1998 12:18:43 +0200. + Date: Sat, 05 Sep 1998 00:59:49 PDT + From: Vern Paxson <vern> + + > %% + > + > "TEST1\n" { fprintf(stderr, "TEST1\n"); yyless(5); } + > ^\n { fprintf(stderr, "empty line\n"); } + > . { } + > \n { fprintf(stderr, "new line\n"); } + > + > %% + > -- input --------------------------------------- + > TEST1 + > -- output -------------------------------------- + > TEST1 + > empty line + > ------------------------------------------------ + + IMHO, it's not clear whether or not this is in fact a bug. It depends + on whether you view yyless() as backing up in the input stream, or as + pushing new characters onto the beginning of the input stream. Flex + interprets it as the latter (for implementation convenience, I'll admit), + and so considers the newline as in fact matching at the beginning of a + line, as after all the last token scanned an entire line and so the + scanner is now at the beginning of a new line. + + I agree that this is counter-intuitive for yyless(), given its + functional description (it's less so for unput(), depending on whether + you're unput()'ing new text or scanned text). But I don't plan to + change it any time soon, as it's a pain to do so. Consequently, + you do indeed need to use yy_set_bol() and YY_AT_BOL() to tweak + your scanner into the behavior you desire. + + Sorry for the less-than-completely-satisfactory answer. + + Vern + + +File: flex.info, Node: unnamed-faq-84, Next: unnamed-faq-85, Prev: unnamed-faq-83, Up: FAQ + +unnamed-faq-84 +============== + + + To: Patrick Krusenotto <krusenot@mac-info-link.de> + Subject: Re: Problems with restarting flex-2.5.2-generated scanner + In-reply-to: Your message of Thu, 24 Sep 1998 10:14:07 PDT. + Date: Thu, 24 Sep 1998 23:28:43 PDT + From: Vern Paxson <vern> + + > I am using flex-2.5.2 and bison 1.25 for Solaris and I am desperately + > trying to make my scanner restart with a new file after my parser stops + > with a parse error. When my compiler restarts, the parser always + > receives the token after the token (in the old file!) that caused the + > parser error. + + I suspect the problem is that your parser has read ahead in order + to attempt to resolve an ambiguity, and when it's restarted it picks + up with that token rather than reading a fresh one. If you're using + yacc, then the special "error" production can sometimes be used to + consume tokens in an attempt to get the parser into a consistent state. + + Vern + + +File: flex.info, Node: unnamed-faq-85, Next: unnamed-faq-86, Prev: unnamed-faq-84, Up: FAQ + +unnamed-faq-85 +============== + + + To: Henric Jungheim <junghelh@pe-nelson.com> + Subject: Re: flex 2.5.4a + In-reply-to: Your message of Tue, 27 Oct 1998 16:41:42 PST. + Date: Tue, 27 Oct 1998 16:50:14 PST + From: Vern Paxson <vern> + + > This brings up a feature request: How about a command line + > option to specify the filename when reading from stdin? That way one + > doesn't need to create a temporary file in order to get the "#line" + > directives to make sense. + + Use -o combined with -t (per the man page description of -o). + + > P.S., Is there any simple way to use non-blocking IO to parse multiple + > streams? + + Simple, no. + + One approach might be to return a magic character on EWOULDBLOCK and + have a rule + + .*<magic-character> // put back .*, eat magic character + + This is off the top of my head, not sure it'll work. + + Vern + + +File: flex.info, Node: unnamed-faq-86, Next: unnamed-faq-87, Prev: unnamed-faq-85, Up: FAQ + +unnamed-faq-86 +============== + + + To: "Repko, Billy D" <billy.d.repko@intel.com> + Subject: Re: Compiling scanners + In-reply-to: Your message of Wed, 13 Jan 1999 10:52:47 PST. + Date: Thu, 14 Jan 1999 00:25:30 PST + From: Vern Paxson <vern> + + > It appears that maybe it cannot find the lfl library. + + The Makefile in the distribution builds it, so you should have it. + It's exceedingly trivial, just a main() that calls yylex() and + a yyrap() that always returns 1. + + > %% + > \n ++num_lines; ++num_chars; + > . ++num_chars; + + You can't indent your rules like this - that's where the errors are coming + from. Flex copies indented text to the output file, it's how you do things + like + + int num_lines_seen = 0; + + to declare local variables. + + Vern + + +File: flex.info, Node: unnamed-faq-87, Next: unnamed-faq-88, Prev: unnamed-faq-86, Up: FAQ + +unnamed-faq-87 +============== + + + To: Erick Branderhorst <Erick.Branderhorst@asml.nl> + Subject: Re: flex input buffer + In-reply-to: Your message of Tue, 09 Feb 1999 13:53:46 PST. + Date: Tue, 09 Feb 1999 21:03:37 PST + From: Vern Paxson <vern> + + > In the flex.skl file the size of the default input buffers is set. Can you + > explain why this size is set and why it is such a high number. + + It's large to optimize performance when scanning large files. You can + safely make it a lot lower if needed. + + Vern + + +File: flex.info, Node: unnamed-faq-88, Next: unnamed-faq-90, Prev: unnamed-faq-87, Up: FAQ + +unnamed-faq-88 +============== + + + To: "Guido Minnen" <guidomi@cogs.susx.ac.uk> + Subject: Re: Flex error message + In-reply-to: Your message of Wed, 24 Feb 1999 15:31:46 PST. + Date: Thu, 25 Feb 1999 00:11:31 PST + From: Vern Paxson <vern> + + > I'm extending a larger scanner written in Flex and I keep running into + > problems. More specifically, I get the error message: + > "flex: input rules are too complicated (>= 32000 NFA states)" + + Increase the definitions in flexdef.h for: + + #define JAMSTATE -32766 /* marks a reference to the state that always j + ams */ + #define MAXIMUM_MNS 31999 + #define BAD_SUBSCRIPT -32767 + + recompile everything, and it should all work. + + Vern + + +File: flex.info, Node: unnamed-faq-90, Next: unnamed-faq-91, Prev: unnamed-faq-88, Up: FAQ + +unnamed-faq-90 +============== + + + To: "Dmitriy Goldobin" <gold@ems.chel.su> + Subject: Re: FLEX trouble + In-reply-to: Your message of Mon, 31 May 1999 18:44:49 PDT. + Date: Tue, 01 Jun 1999 00:15:07 PDT + From: Vern Paxson <vern> + + > I have a trouble with FLEX. Why rule "/*".*"*/" work properly,=20 + > but rule "/*"(.|\n)*"*/" don't work ? + + The second of these will have to scan the entire input stream (because + "(.|\n)*" matches an arbitrary amount of any text) in order to see if + it ends with "*/", terminating the comment. That potentially will overflow + the input buffer. + + > More complex rule "/*"([^*]|(\*/[^/]))*"*/ give an error + > 'unrecognized rule'. + + You can't use the '/' operator inside parentheses. It's not clear + what "(a/b)*" actually means. + + > I now use workaround with state <comment>, but single-rule is + > better, i think. + + Single-rule is nice but will always have the problem of either setting + restrictions on comments (like not allowing multi-line comments) and/or + running the risk of consuming the entire input stream, as noted above. + + Vern + + +File: flex.info, Node: unnamed-faq-91, Next: unnamed-faq-92, Prev: unnamed-faq-90, Up: FAQ + +unnamed-faq-91 +============== + + + Received: from mc-qout4.whowhere.com (mc-qout4.whowhere.com [209.185.123.18]) + by ee.lbl.gov (8.9.3/8.9.3) with SMTP id IAA05100 + for <vern@ee.lbl.gov>; Tue, 15 Jun 1999 08:56:06 -0700 (PDT) + Received: from Unknown/Local ([?.?.?.?]) by my-deja.com; Tue Jun 15 08:55:43 1999 + To: vern@ee.lbl.gov + Date: Tue, 15 Jun 1999 08:55:43 -0700 + From: "Aki Niimura" <neko@my-deja.com> + Message-ID: <KNONDOHDOBGAEAAA@my-deja.com> + Mime-Version: 1.0 + Cc: + X-Sent-Mail: on + Reply-To: + X-Mailer: MailCity Service + Subject: A question on flex C++ scanner + X-Sender-Ip: 12.72.207.61 + Organization: My Deja Email (http://www.my-deja.com:80) + Content-Type: text/plain; charset=us-ascii + Content-Transfer-Encoding: 7bit + + Dear Dr. Paxon, + + I have been using flex for years. + It works very well on many projects. + Most case, I used it to generate a scanner on C language. + However, one project I needed to generate a scanner + on C++ lanuage. Thanks to your enhancement, flex did + the job. + + Currently, I'm working on enhancing my previous project. + I need to deal with multiple input streams (recursive + inclusion) in this scanner (C++). + I did similar thing for another scanner (C) as you + explained in your documentation. + + The generated scanner (C++) has necessary methods: + - switch_to_buffer(struct yy_buffer_state *b) + - yy_create_buffer(istream *is, int sz) + - yy_delete_buffer(struct yy_buffer_state *b) + + However, I couldn't figure out how to access current + buffer (yy_current_buffer). + + yy_current_buffer is a protected member of yyFlexLexer. + I can't access it directly. + Then, I thought yy_create_buffer() with is = 0 might + return current stream buffer. But it seems not as far + as I checked the source. (flex 2.5.4) + + I went through the Web in addition to Flex documentation. + However, it hasn't been successful, so far. + + It is not my intention to bother you, but, can you + comment about how to obtain the current stream buffer? + + Your response would be highly appreciated. + + Best regards, + Aki Niimura + + --== Sent via Deja.com http://www.deja.com/ ==-- + Share what you know. Learn what you don't. + + +File: flex.info, Node: unnamed-faq-92, Next: unnamed-faq-93, Prev: unnamed-faq-91, Up: FAQ + +unnamed-faq-92 +============== + + + To: neko@my-deja.com + Subject: Re: A question on flex C++ scanner + In-reply-to: Your message of Tue, 15 Jun 1999 08:55:43 PDT. + Date: Tue, 15 Jun 1999 09:04:24 PDT + From: Vern Paxson <vern> + + > However, I couldn't figure out how to access current + > buffer (yy_current_buffer). + + Derive your own subclass from yyFlexLexer. + + Vern + + +File: flex.info, Node: unnamed-faq-93, Next: unnamed-faq-94, Prev: unnamed-faq-92, Up: FAQ + +unnamed-faq-93 +============== + + + To: "Stones, Darren" <Darren.Stones@nectech.co.uk> + Subject: Re: You're the man to see? + In-reply-to: Your message of Wed, 23 Jun 1999 11:10:29 PDT. + Date: Wed, 23 Jun 1999 09:01:40 PDT + From: Vern Paxson <vern> + + > I hope you can help me. I am using Flex and Bison to produce an interpreted + > language. However all goes well until I try to implement an IF statement or + > a WHILE. I cannot get this to work as the parser parses all the conditions + > eg. the TRUE and FALSE conditons to check for a rule match. So I cannot + > make a decision!! + + You need to use the parser to build a parse tree (= abstract syntax trwee), + and when that's all done you recursively evaluate the tree, binding variables + to values at that time. + + Vern + + +File: flex.info, Node: unnamed-faq-94, Next: unnamed-faq-95, Prev: unnamed-faq-93, Up: FAQ + +unnamed-faq-94 +============== + + + To: Petr Danecek <petr@ics.cas.cz> + Subject: Re: flex - question + In-reply-to: Your message of Mon, 28 Jun 1999 19:21:41 PDT. + Date: Fri, 02 Jul 1999 16:52:13 PDT + From: Vern Paxson <vern> + + > file, it takes an enormous amount of time. It is funny, because the + > source code has only 12 rules!!! I think it looks like an exponencial + > growth. + + Right, that's the problem - some patterns (those with a lot of + ambiguity, where yours has because at any given time the scanner can + be in the middle of all sorts of combinations of the different + rules) blow up exponentially. + + For your rules, there is an easy fix. Change the ".*" that comes fater + the directory name to "[^ ]*". With that in place, the rules are no + longer nearly so ambiguous, because then once one of the directories + has been matched, no other can be matched (since they all require a + leading blank). + + If that's not an acceptable solution, then you can enter a start state + to pick up the .*\n after each directory is matched. + + Also note that for speed, you'll want to add a ".*" rule at the end, + otherwise rules that don't match any of the patterns will be matched + very slowly, a character at a time. + + Vern + + +File: flex.info, Node: unnamed-faq-95, Next: unnamed-faq-96, Prev: unnamed-faq-94, Up: FAQ + +unnamed-faq-95 +============== + + + To: Tielman Koekemoer <tielman@spi.co.za> + Subject: Re: Please help. + In-reply-to: Your message of Thu, 08 Jul 1999 13:20:37 PDT. + Date: Thu, 08 Jul 1999 08:20:39 PDT + From: Vern Paxson <vern> + + > I was hoping you could help me with my problem. + > + > I tried compiling (gnu)flex on a Solaris 2.4 machine + > but when I ran make (after configure) I got an error. + > + > -------------------------------------------------------------- + > gcc -c -I. -I. -g -O parse.c + > ./flex -t -p ./scan.l >scan.c + > sh: ./flex: not found + > *** Error code 1 + > make: Fatal error: Command failed for target `scan.c' + > ------------------------------------------------------------- + > + > What's strange to me is that I'm only + > trying to install flex now. I then edited the Makefile to + > and changed where it says "FLEX = flex" to "FLEX = lex" + > ( lex: the native Solaris one ) but then it complains about + > the "-p" option. Is there any way I can compile flex without + > using flex or lex? + > + > Thanks so much for your time. + + You managed to step on the bootstrap sequence, which first copies + initscan.c to scan.c in order to build flex. Try fetching a fresh + distribution from ftp.ee.lbl.gov. (Or you can first try removing + ".bootstrap" and doing a make again.) + + Vern + + +File: flex.info, Node: unnamed-faq-96, Next: unnamed-faq-97, Prev: unnamed-faq-95, Up: FAQ + +unnamed-faq-96 +============== + + + To: Tielman Koekemoer <tielman@spi.co.za> + Subject: Re: Please help. + In-reply-to: Your message of Fri, 09 Jul 1999 09:16:14 PDT. + Date: Fri, 09 Jul 1999 00:27:20 PDT + From: Vern Paxson <vern> + + > First I removed .bootstrap (and ran make) - no luck. I downloaded the + > software but I still have the same problem. Is there anything else I + > could try. + + Try: + + cp initscan.c scan.c + touch scan.c + make scan.o + + If this last tries to first build scan.c from scan.l using ./flex, then + your "make" is broken, in which case compile scan.c to scan.o by hand. + + Vern + + +File: flex.info, Node: unnamed-faq-97, Next: unnamed-faq-98, Prev: unnamed-faq-96, Up: FAQ + +unnamed-faq-97 +============== + + + To: Sumanth Kamenani <skamenan@crl.nmsu.edu> + Subject: Re: Error + In-reply-to: Your message of Mon, 19 Jul 1999 23:08:41 PDT. + Date: Tue, 20 Jul 1999 00:18:26 PDT + From: Vern Paxson <vern> + + > I am getting a compilation error. The error is given as "unknown symbol- yylex". + + The parser relies on calling yylex(), but you're instead using the C++ scanning + class, so you need to supply a yylex() "glue" function that calls an instance + scanner of the scanner (e.g., "scanner->yylex()"). + + Vern + + +File: flex.info, Node: unnamed-faq-98, Next: unnamed-faq-99, Prev: unnamed-faq-97, Up: FAQ + +unnamed-faq-98 +============== + + + To: daniel@synchrods.synchrods.COM (Daniel Senderowicz) + Subject: Re: lex + In-reply-to: Your message of Mon, 22 Nov 1999 11:19:04 PST. + Date: Tue, 23 Nov 1999 15:54:30 PST + From: Vern Paxson <vern> + + Well, your problem is the + + switch (yybgin-yysvec-1) { /* witchcraft */ + + at the beginning of lex rules. "witchcraft" == "non-portable". It's + assuming knowledge of the AT&T lex's internal variables. + + For flex, you can probably do the equivalent using a switch on YYSTATE. + + Vern + + +File: flex.info, Node: unnamed-faq-99, Next: unnamed-faq-100, Prev: unnamed-faq-98, Up: FAQ + +unnamed-faq-99 +============== + + + To: archow@hss.hns.com + Subject: Re: Regarding distribution of flex and yacc based grammars + In-reply-to: Your message of Sun, 19 Dec 1999 17:50:24 +0530. + Date: Wed, 22 Dec 1999 01:56:24 PST + From: Vern Paxson <vern> + + > When we provide the customer with an object code distribution, is it + > necessary for us to provide source + > for the generated C files from flex and bison since they are generated by + > flex and bison ? + + For flex, no. I don't know what the current state of this is for bison. + + > Also, is there any requrirement for us to neccessarily provide source for + > the grammar files which are fed into flex and bison ? + + Again, for flex, no. + + See the file "COPYING" in the flex distribution for the legalese. + + Vern + + +File: flex.info, Node: unnamed-faq-100, Next: unnamed-faq-101, Prev: unnamed-faq-99, Up: FAQ + +unnamed-faq-100 +=============== + + + To: Martin Gallwey <gallweym@hyperion.moe.ul.ie> + Subject: Re: Flex, and self referencing rules + In-reply-to: Your message of Sun, 20 Feb 2000 01:01:21 PST. + Date: Sat, 19 Feb 2000 18:33:16 PST + From: Vern Paxson <vern> + + > However, I do not use unput anywhere. I do use self-referencing + > rules like this: + > + > UnaryExpr ({UnionExpr})|("-"{UnaryExpr}) + + You can't do this - flex is *not* a parser like yacc (which does indeed + allow recursion), it is a scanner that's confined to regular expressions. + + Vern + + +File: flex.info, Node: unnamed-faq-101, Next: What is the difference between YYLEX_PARAM and YY_DECL?, Prev: unnamed-faq-100, Up: FAQ + +unnamed-faq-101 +=============== + + + To: slg3@lehigh.edu (SAMUEL L. GULDEN) + Subject: Re: Flex problem + In-reply-to: Your message of Thu, 02 Mar 2000 12:29:04 PST. + Date: Thu, 02 Mar 2000 23:00:46 PST + From: Vern Paxson <vern> + + If this is exactly your program: + + > digit [0-9] + > digits {digit}+ + > whitespace [ \t\n]+ + > + > %% + > "[" { printf("open_brac\n");} + > "]" { printf("close_brac\n");} + > "+" { printf("addop\n");} + > "*" { printf("multop\n");} + > {digits} { printf("NUMBER = %s\n", yytext);} + > whitespace ; + + then the problem is that the last rule needs to be "{whitespace}" ! + + Vern + + +File: flex.info, Node: What is the difference between YYLEX_PARAM and YY_DECL?, Next: Why do I get "conflicting types for yylex" error?, Prev: unnamed-faq-101, Up: FAQ + +What is the difference between YYLEX_PARAM and YY_DECL? +======================================================= + +YYLEX_PARAM is not a flex symbol. It is for Bison. It tells Bison to +pass extra params when it calls yylex() from the parser. + + YY_DECL is the Flex declaration of yylex. The default is similar to +this: + + + #define int yy_lex () + + +File: flex.info, Node: Why do I get "conflicting types for yylex" error?, Next: How do I access the values set in a Flex action from within a Bison action?, Prev: What is the difference between YYLEX_PARAM and YY_DECL?, Up: FAQ + +Why do I get "conflicting types for yylex" error? +================================================= + +This is a compiler error regarding a generated Bison parser, not a Flex +scanner. It means you need a prototype of yylex() in the top of the +Bison file. Be sure the prototype matches YY_DECL. + + +File: flex.info, Node: How do I access the values set in a Flex action from within a Bison action?, Prev: Why do I get "conflicting types for yylex" error?, Up: FAQ + +How do I access the values set in a Flex action from within a Bison action? +=========================================================================== + +With $1, $2, $3, etc. These are called "Semantic Values" in the Bison +manual. See *Note Top: (bison)Top. + + +File: flex.info, Node: Appendices, Next: Indices, Prev: FAQ, Up: Top + +Appendix A Appendices +********************* + +* Menu: + +* Makefiles and Flex:: +* Bison Bridge:: +* M4 Dependency:: +* Common Patterns:: + + +File: flex.info, Node: Makefiles and Flex, Next: Bison Bridge, Prev: Appendices, Up: Appendices + +A.1 Makefiles and Flex +====================== + +In this appendix, we provide tips for writing Makefiles to build your +scanners. + + In a traditional build environment, we say that the `.c' files are +the sources, and the `.o' files are the intermediate files. When using +`flex', however, the `.l' files are the sources, and the generated `.c' +files (along with the `.o' files) are the intermediate files. This +requires you to carefully plan your Makefile. + + Modern `make' programs understand that `foo.l' is intended to +generate `lex.yy.c' or `foo.c', and will behave accordingly(1)(2). The +following Makefile does not explicitly instruct `make' how to build +`foo.c' from `foo.l'. Instead, it relies on the implicit rules of the +`make' program to build the intermediate file, `scan.c': + + + # Basic Makefile -- relies on implicit rules + # Creates "myprogram" from "scan.l" and "myprogram.c" + # + LEX=flex + myprogram: scan.o myprogram.o + scan.o: scan.l + + For simple cases, the above may be sufficient. For other cases, you +may have to explicitly instruct `make' how to build your scanner. The +following is an example of a Makefile containing explicit rules: + + + # Basic Makefile -- provides explicit rules + # Creates "myprogram" from "scan.l" and "myprogram.c" + # + LEX=flex + myprogram: scan.o myprogram.o + $(CC) -o $@ $(LDFLAGS) $^ + + myprogram.o: myprogram.c + $(CC) $(CPPFLAGS) $(CFLAGS) -o $@ -c $^ + + scan.o: scan.c + $(CC) $(CPPFLAGS) $(CFLAGS) -o $@ -c $^ + + scan.c: scan.l + $(LEX) $(LFLAGS) -o $@ $^ + + clean: + $(RM) *.o scan.c + + Notice in the above example that `scan.c' is in the `clean' target. +This is because we consider the file `scan.c' to be an intermediate +file. + + Finally, we provide a realistic example of a `flex' scanner used +with a `bison' parser(3). There is a tricky problem we have to deal +with. Since a `flex' scanner will typically include a header file +(e.g., `y.tab.h') generated by the parser, we need to be sure that the +header file is generated BEFORE the scanner is compiled. We handle this +case in the following example: + + + # Makefile example -- scanner and parser. + # Creates "myprogram" from "scan.l", "parse.y", and "myprogram.c" + # + LEX = flex + YACC = bison -y + YFLAGS = -d + objects = scan.o parse.o myprogram.o + + myprogram: $(objects) + scan.o: scan.l parse.c + parse.o: parse.y + myprogram.o: myprogram.c + + In the above example, notice the line, + + + scan.o: scan.l parse.c + + , which lists the file `parse.c' (the generated parser) as a +dependency of `scan.o'. We want to ensure that the parser is created +before the scanner is compiled, and the above line seems to do the +trick. Feel free to experiment with your specific implementation of +`make'. + + For more details on writing Makefiles, see *Note Top: (make)Top. + + ---------- Footnotes ---------- + + (1) GNU `make' and GNU `automake' are two such programs that provide +implicit rules for flex-generated scanners. + + (2) GNU `automake' may generate code to execute flex in +lex-compatible mode, or to stdout. If this is not what you want, then +you should provide an explicit rule in your Makefile.am + + (3) This example also applies to yacc parsers. + + +File: flex.info, Node: Bison Bridge, Next: M4 Dependency, Prev: Makefiles and Flex, Up: Appendices + +A.2 C Scanners with Bison Parsers +================================= + +This section describes the `flex' features useful when integrating +`flex' with `GNU bison'(1). Skip this section if you are not using +`bison' with your scanner. Here we discuss only the `flex' half of the +`flex' and `bison' pair. We do not discuss `bison' in any detail. For +more information about generating `bison' parsers, see *Note Top: +(bison)Top. + + A compatible `bison' scanner is generated by declaring `%option +bison-bridge' or by supplying `--bison-bridge' when invoking `flex' +from the command line. This instructs `flex' that the macro `yylval' +may be used. The data type for `yylval', `YYSTYPE', is typically +defined in a header file, included in section 1 of the `flex' input +file. For a list of functions and macros available, *Note +bison-functions::. + + The declaration of yylex becomes, + + + int yylex ( YYSTYPE * lvalp, yyscan_t scanner ); + + If `%option bison-locations' is specified, then the declaration +becomes, + + + int yylex ( YYSTYPE * lvalp, YYLTYPE * llocp, yyscan_t scanner ); + + Note that the macros `yylval' and `yylloc' evaluate to pointers. +Support for `yylloc' is optional in `bison', so it is optional in +`flex' as well. The following is an example of a `flex' scanner that is +compatible with `bison'. + + + /* Scanner for "C" assignment statements... sort of. */ + %{ + #include "y.tab.h" /* Generated by bison. */ + %} + + %option bison-bridge bison-locations + % + + [[:digit:]]+ { yylval->num = atoi(yytext); return NUMBER;} + [[:alnum:]]+ { yylval->str = strdup(yytext); return STRING;} + "="|";" { return yytext[0];} + . {} + % + + As you can see, there really is no magic here. We just use `yylval' +as we would any other variable. The data type of `yylval' is generated +by `bison', and included in the file `y.tab.h'. Here is the +corresponding `bison' parser: + + + /* Parser to convert "C" assignments to lisp. */ + %{ + /* Pass the argument to yyparse through to yylex. */ + #define YYPARSE_PARAM scanner + #define YYLEX_PARAM scanner + %} + %locations + %pure_parser + %union { + int num; + char* str; + } + %token <str> STRING + %token <num> NUMBER + %% + assignment: + STRING '=' NUMBER ';' { + printf( "(setf %s %d)", $1, $3 ); + } + ; + + ---------- Footnotes ---------- + + (1) The features described here are purely optional, and are by no +means the only way to use flex with bison. We merely provide some glue +to ease development of your parser-scanner pair. + + +File: flex.info, Node: M4 Dependency, Next: Common Patterns, Prev: Bison Bridge, Up: Appendices + +A.3 M4 Dependency +================= + +The macro processor `m4'(1) must be installed wherever flex is +installed. `flex' invokes `m4', found by searching the directories in +the `PATH' environment variable. Any code you place in section 1 or in +the actions will be sent through m4. Please follow these rules to +protect your code from unwanted `m4' processing. + + * Do not use symbols that begin with, `m4_', such as, `m4_define', + or `m4_include', since those are reserved for `m4' macro names. If + for some reason you need m4_ as a prefix, use a preprocessor + #define to get your symbol past m4 unmangled. + + * Do not use the strings `[[' or `]]' anywhere in your code. The + former is not valid in C, except within comments and strings, but + the latter is valid in code such as `x[y[z]]'. The solution is + simple. To get the literal string `"]]"', use `"]""]"'. To get the + array notation `x[y[z]]', use `x[y[z] ]'. Flex will attempt to + detect these sequences in user code, and escape them. However, + it's best to avoid this complexity where possible, by removing + such sequences from your code. + + + `m4' is only required at the time you run `flex'. The generated +scanner is ordinary C or C++, and does _not_ require `m4'. + + ---------- Footnotes ---------- + + (1) The use of m4 is subject to change in future revisions of flex. +It is not part of the public API of flex. Do not depend on it. + + +File: flex.info, Node: Common Patterns, Prev: M4 Dependency, Up: Appendices + +A.4 Common Patterns +=================== + +This appendix provides examples of common regular expressions you might +use in your scanner. + +* Menu: + +* Numbers:: +* Identifiers:: +* Quoted Constructs:: +* Addresses:: + + +File: flex.info, Node: Numbers, Next: Identifiers, Up: Common Patterns + +A.4.1 Numbers +------------- + +C99 decimal constant + `([[:digit:]]{-}[0])[[:digit:]]*' + +C99 hexadecimal constant + `0[xX][[:xdigit:]]+' + +C99 octal constant + `0[0123456]*' + +C99 floating point constant + + {dseq} ([[:digit:]]+) + {dseq_opt} ([[:digit:]]*) + {frac} (({dseq_opt}"."{dseq})|{dseq}".") + {exp} ([eE][+-]?{dseq}) + {exp_opt} ({exp}?) + {fsuff} [flFL] + {fsuff_opt} ({fsuff}?) + {hpref} (0[xX]) + {hdseq} ([[:xdigit:]]+) + {hdseq_opt} ([[:xdigit:]]*) + {hfrac} (({hdseq_opt}"."{hdseq})|({hdseq}".")) + {bexp} ([pP][+-]?{dseq}) + {dfc} (({frac}{exp_opt}{fsuff_opt})|({dseq}{exp}{fsuff_opt})) + {hfc} (({hpref}{hfrac}{bexp}{fsuff_opt})|({hpref}{hdseq}{bexp}{fsuff_opt})) + + {c99_floating_point_constant} ({dfc}|{hfc}) + + See C99 section 6.4.4.2 for the gory details. + + + +File: flex.info, Node: Identifiers, Next: Quoted Constructs, Prev: Numbers, Up: Common Patterns + +A.4.2 Identifiers +----------------- + +C99 Identifier + + ucn ((\\u([[:xdigit:]]{4}))|(\\U([[:xdigit:]]{8}))) + nondigit [_[:alpha:]] + c99_id ([_[:alpha:]]|{ucn})([_[:alnum:]]|{ucn})* + + Technically, the above pattern does not encompass all possible C99 + identifiers, since C99 allows for "implementation-defined" + characters. In practice, C compilers follow the above pattern, + with the addition of the `$' character. + +UTF-8 Encoded Unicode Code Point + + [\x09\x0A\x0D\x20-\x7E]|[\xC2-\xDF][\x80-\xBF]|\xE0[\xA0-\xBF][\x80-\xBF]|[\xE1-\xEC\xEE\xEF]([\x80-\xBF]{2})|\xED[\x80-\x9F][\x80-\xBF]|\xF0[\x90-\xBF]([\x80-\xBF]{2})|[\xF1-\xF3]([\x80-\xBF]{3})|\xF4[\x80-\x8F]([\x80-\xBF]{2}) + + + +File: flex.info, Node: Quoted Constructs, Next: Addresses, Prev: Identifiers, Up: Common Patterns + +A.4.3 Quoted Constructs +----------------------- + +C99 String Literal + `L?\"([^\"\\\n]|(\\['\"?\\abfnrtv])|(\\([0123456]{1,3}))|(\\x[[:xdigit:]]+)|(\\u([[:xdigit:]]{4}))|(\\U([[:xdigit:]]{8})))*\"' + +C99 Comment + `("/*"([^*]|"*"[^/])*"*/")|("/"(\\\n)*"/"[^\n]*)' + + Note that in C99, a `//'-style comment may be split across lines, + and, contrary to popular belief, does not include the trailing + `\n' character. + + A better way to scan `/* */' comments is by line, rather than + matching possibly huge comments all at once. This will allow you + to scan comments of unlimited length, as long as line breaks + appear at sane intervals. This is also more efficient when used + with automatic line number processing. *Note option-yylineno::. + + + <INITIAL>{ + "/*" BEGIN(COMMENT); + } + <COMMENT>{ + "*/" BEGIN(0); + [^*\n]+ ; + "*"[^/] ; + \n ; + } + + + +File: flex.info, Node: Addresses, Prev: Quoted Constructs, Up: Common Patterns + +A.4.4 Addresses +--------------- + +IPv4 Address + `(([[:digit:]]{1,3}"."){3}([[:digit:]]{1,3}))' + +IPv6 Address + + hex4 ([[:xdigit:]]{1,4}) + hexseq ({hex4}(:{hex4}*)) + hexpart ({hexseq}|({hexseq}::({hexseq}?))|::{hexseq}) + IPv6address ({hexpart}(":"{IPv4address})?) + + See RFC2373 for details. + +URI + `(([^:/?#]+):)?("//"([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))?' + + This pattern is nearly useless, since it allows just about any + character to appear in a URI, including spaces and control + characters. See RFC2396 for details. + + + +File: flex.info, Node: Indices, Prev: Appendices, Up: Top + +Indices +******* + +* Menu: + +* Concept Index:: +* Index of Functions and Macros:: +* Index of Variables:: +* Index of Data Types:: +* Index of Hooks:: +* Index of Scanner Options:: + |