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+<html>
+<head>
+<title>pcreapi specification</title>
+</head>
+<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
+<h1>pcreapi man page</h1>
+<p>
+Return to the <a href="index.html">PCRE index page</a>.
+</p>
+<p>
+This page is part of the PCRE HTML documentation. It was generated automatically
+from the original man page. If there is any nonsense in it, please consult the
+man page, in case the conversion went wrong.
+<br>
+<ul>
+<li><a name="TOC1" href="#SEC1">PCRE NATIVE API BASIC FUNCTIONS</a>
+<li><a name="TOC2" href="#SEC2">PCRE NATIVE API STRING EXTRACTION FUNCTIONS</a>
+<li><a name="TOC3" href="#SEC3">PCRE NATIVE API AUXILIARY FUNCTIONS</a>
+<li><a name="TOC4" href="#SEC4">PCRE NATIVE API INDIRECTED FUNCTIONS</a>
+<li><a name="TOC5" href="#SEC5">PCRE 8-BIT, 16-BIT, AND 32-BIT LIBRARIES</a>
+<li><a name="TOC6" href="#SEC6">PCRE API OVERVIEW</a>
+<li><a name="TOC7" href="#SEC7">NEWLINES</a>
+<li><a name="TOC8" href="#SEC8">MULTITHREADING</a>
+<li><a name="TOC9" href="#SEC9">SAVING PRECOMPILED PATTERNS FOR LATER USE</a>
+<li><a name="TOC10" href="#SEC10">CHECKING BUILD-TIME OPTIONS</a>
+<li><a name="TOC11" href="#SEC11">COMPILING A PATTERN</a>
+<li><a name="TOC12" href="#SEC12">COMPILATION ERROR CODES</a>
+<li><a name="TOC13" href="#SEC13">STUDYING A PATTERN</a>
+<li><a name="TOC14" href="#SEC14">LOCALE SUPPORT</a>
+<li><a name="TOC15" href="#SEC15">INFORMATION ABOUT A PATTERN</a>
+<li><a name="TOC16" href="#SEC16">REFERENCE COUNTS</a>
+<li><a name="TOC17" href="#SEC17">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a>
+<li><a name="TOC18" href="#SEC18">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a>
+<li><a name="TOC19" href="#SEC19">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a>
+<li><a name="TOC20" href="#SEC20">DUPLICATE SUBPATTERN NAMES</a>
+<li><a name="TOC21" href="#SEC21">FINDING ALL POSSIBLE MATCHES</a>
+<li><a name="TOC22" href="#SEC22">OBTAINING AN ESTIMATE OF STACK USAGE</a>
+<li><a name="TOC23" href="#SEC23">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a>
+<li><a name="TOC24" href="#SEC24">SEE ALSO</a>
+<li><a name="TOC25" href="#SEC25">AUTHOR</a>
+<li><a name="TOC26" href="#SEC26">REVISION</a>
+</ul>
+<P>
+<b>#include &#60;pcre.h&#62;</b>
+</P>
+<br><a name="SEC1" href="#TOC1">PCRE NATIVE API BASIC FUNCTIONS</a><br>
+<P>
+<b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
+<b> const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
+<b> const unsigned char *<i>tableptr</i>);</b>
+<br>
+<br>
+<b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
+<b> int *<i>errorcodeptr</i>,</b>
+<b> const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
+<b> const unsigned char *<i>tableptr</i>);</b>
+<br>
+<br>
+<b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i>,</b>
+<b> const char **<i>errptr</i>);</b>
+<br>
+<br>
+<b>void pcre_free_study(pcre_extra *<i>extra</i>);</b>
+<br>
+<br>
+<b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
+<b> const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
+<b> int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
+<br>
+<br>
+<b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
+<b> const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
+<b> int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
+<b> int *<i>workspace</i>, int <i>wscount</i>);</b>
+</P>
+<br><a name="SEC2" href="#TOC1">PCRE NATIVE API STRING EXTRACTION FUNCTIONS</a><br>
+<P>
+<b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
+<b> const char *<i>subject</i>, int *<i>ovector</i>,</b>
+<b> int <i>stringcount</i>, const char *<i>stringname</i>,</b>
+<b> char *<i>buffer</i>, int <i>buffersize</i>);</b>
+<br>
+<br>
+<b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
+<b> int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
+<b> int <i>buffersize</i>);</b>
+<br>
+<br>
+<b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
+<b> const char *<i>subject</i>, int *<i>ovector</i>,</b>
+<b> int <i>stringcount</i>, const char *<i>stringname</i>,</b>
+<b> const char **<i>stringptr</i>);</b>
+<br>
+<br>
+<b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
+<b> const char *<i>name</i>);</b>
+<br>
+<br>
+<b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
+<b> const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
+<br>
+<br>
+<b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
+<b> int <i>stringcount</i>, int <i>stringnumber</i>,</b>
+<b> const char **<i>stringptr</i>);</b>
+<br>
+<br>
+<b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
+<b> int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
+<br>
+<br>
+<b>void pcre_free_substring(const char *<i>stringptr</i>);</b>
+<br>
+<br>
+<b>void pcre_free_substring_list(const char **<i>stringptr</i>);</b>
+</P>
+<br><a name="SEC3" href="#TOC1">PCRE NATIVE API AUXILIARY FUNCTIONS</a><br>
+<P>
+<b>int pcre_jit_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
+<b> const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
+<b> int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
+<b> pcre_jit_stack *<i>jstack</i>);</b>
+<br>
+<br>
+<b>pcre_jit_stack *pcre_jit_stack_alloc(int <i>startsize</i>, int <i>maxsize</i>);</b>
+<br>
+<br>
+<b>void pcre_jit_stack_free(pcre_jit_stack *<i>stack</i>);</b>
+<br>
+<br>
+<b>void pcre_assign_jit_stack(pcre_extra *<i>extra</i>,</b>
+<b> pcre_jit_callback <i>callback</i>, void *<i>data</i>);</b>
+<br>
+<br>
+<b>const unsigned char *pcre_maketables(void);</b>
+<br>
+<br>
+<b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
+<b> int <i>what</i>, void *<i>where</i>);</b>
+<br>
+<br>
+<b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
+<br>
+<br>
+<b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
+<br>
+<br>
+<b>const char *pcre_version(void);</b>
+<br>
+<br>
+<b>int pcre_pattern_to_host_byte_order(pcre *<i>code</i>,</b>
+<b> pcre_extra *<i>extra</i>, const unsigned char *<i>tables</i>);</b>
+</P>
+<br><a name="SEC4" href="#TOC1">PCRE NATIVE API INDIRECTED FUNCTIONS</a><br>
+<P>
+<b>void *(*pcre_malloc)(size_t);</b>
+<br>
+<br>
+<b>void (*pcre_free)(void *);</b>
+<br>
+<br>
+<b>void *(*pcre_stack_malloc)(size_t);</b>
+<br>
+<br>
+<b>void (*pcre_stack_free)(void *);</b>
+<br>
+<br>
+<b>int (*pcre_callout)(pcre_callout_block *);</b>
+<br>
+<br>
+<b>int (*pcre_stack_guard)(void);</b>
+</P>
+<br><a name="SEC5" href="#TOC1">PCRE 8-BIT, 16-BIT, AND 32-BIT LIBRARIES</a><br>
+<P>
+As well as support for 8-bit character strings, PCRE also supports 16-bit
+strings (from release 8.30) and 32-bit strings (from release 8.32), by means of
+two additional libraries. They can be built as well as, or instead of, the
+8-bit library. To avoid too much complication, this document describes the
+8-bit versions of the functions, with only occasional references to the 16-bit
+and 32-bit libraries.
+</P>
+<P>
+The 16-bit and 32-bit functions operate in the same way as their 8-bit
+counterparts; they just use different data types for their arguments and
+results, and their names start with <b>pcre16_</b> or <b>pcre32_</b> instead of
+<b>pcre_</b>. For every option that has UTF8 in its name (for example,
+PCRE_UTF8), there are corresponding 16-bit and 32-bit names with UTF8 replaced
+by UTF16 or UTF32, respectively. This facility is in fact just cosmetic; the
+16-bit and 32-bit option names define the same bit values.
+</P>
+<P>
+References to bytes and UTF-8 in this document should be read as references to
+16-bit data units and UTF-16 when using the 16-bit library, or 32-bit data
+units and UTF-32 when using the 32-bit library, unless specified otherwise.
+More details of the specific differences for the 16-bit and 32-bit libraries
+are given in the
+<a href="pcre16.html"><b>pcre16</b></a>
+and
+<a href="pcre32.html"><b>pcre32</b></a>
+pages.
+</P>
+<br><a name="SEC6" href="#TOC1">PCRE API OVERVIEW</a><br>
+<P>
+PCRE has its own native API, which is described in this document. There are
+also some wrapper functions (for the 8-bit library only) that correspond to the
+POSIX regular expression API, but they do not give access to all the
+functionality. They are described in the
+<a href="pcreposix.html"><b>pcreposix</b></a>
+documentation. Both of these APIs define a set of C function calls. A C++
+wrapper (again for the 8-bit library only) is also distributed with PCRE. It is
+documented in the
+<a href="pcrecpp.html"><b>pcrecpp</b></a>
+page.
+</P>
+<P>
+The native API C function prototypes are defined in the header file
+<b>pcre.h</b>, and on Unix-like systems the (8-bit) library itself is called
+<b>libpcre</b>. It can normally be accessed by adding <b>-lpcre</b> to the
+command for linking an application that uses PCRE. The header file defines the
+macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor release numbers
+for the library. Applications can use these to include support for different
+releases of PCRE.
+</P>
+<P>
+In a Windows environment, if you want to statically link an application program
+against a non-dll <b>pcre.a</b> file, you must define PCRE_STATIC before
+including <b>pcre.h</b> or <b>pcrecpp.h</b>, because otherwise the
+<b>pcre_malloc()</b> and <b>pcre_free()</b> exported functions will be declared
+<b>__declspec(dllimport)</b>, with unwanted results.
+</P>
+<P>
+The functions <b>pcre_compile()</b>, <b>pcre_compile2()</b>, <b>pcre_study()</b>,
+and <b>pcre_exec()</b> are used for compiling and matching regular expressions
+in a Perl-compatible manner. A sample program that demonstrates the simplest
+way of using them is provided in the file called <i>pcredemo.c</i> in the PCRE
+source distribution. A listing of this program is given in the
+<a href="pcredemo.html"><b>pcredemo</b></a>
+documentation, and the
+<a href="pcresample.html"><b>pcresample</b></a>
+documentation describes how to compile and run it.
+</P>
+<P>
+Just-in-time compiler support is an optional feature of PCRE that can be built
+in appropriate hardware environments. It greatly speeds up the matching
+performance of many patterns. Simple programs can easily request that it be
+used if available, by setting an option that is ignored when it is not
+relevant. More complicated programs might need to make use of the functions
+<b>pcre_jit_stack_alloc()</b>, <b>pcre_jit_stack_free()</b>, and
+<b>pcre_assign_jit_stack()</b> in order to control the JIT code's memory usage.
+</P>
+<P>
+From release 8.32 there is also a direct interface for JIT execution, which
+gives improved performance. The JIT-specific functions are discussed in the
+<a href="pcrejit.html"><b>pcrejit</b></a>
+documentation.
+</P>
+<P>
+A second matching function, <b>pcre_dfa_exec()</b>, which is not
+Perl-compatible, is also provided. This uses a different algorithm for the
+matching. The alternative algorithm finds all possible matches (at a given
+point in the subject), and scans the subject just once (unless there are
+lookbehind assertions). However, this algorithm does not return captured
+substrings. A description of the two matching algorithms and their advantages
+and disadvantages is given in the
+<a href="pcrematching.html"><b>pcrematching</b></a>
+documentation.
+</P>
+<P>
+In addition to the main compiling and matching functions, there are convenience
+functions for extracting captured substrings from a subject string that is
+matched by <b>pcre_exec()</b>. They are:
+<pre>
+ <b>pcre_copy_substring()</b>
+ <b>pcre_copy_named_substring()</b>
+ <b>pcre_get_substring()</b>
+ <b>pcre_get_named_substring()</b>
+ <b>pcre_get_substring_list()</b>
+ <b>pcre_get_stringnumber()</b>
+ <b>pcre_get_stringtable_entries()</b>
+</pre>
+<b>pcre_free_substring()</b> and <b>pcre_free_substring_list()</b> are also
+provided, to free the memory used for extracted strings.
+</P>
+<P>
+The function <b>pcre_maketables()</b> is used to build a set of character tables
+in the current locale for passing to <b>pcre_compile()</b>, <b>pcre_exec()</b>,
+or <b>pcre_dfa_exec()</b>. This is an optional facility that is provided for
+specialist use. Most commonly, no special tables are passed, in which case
+internal tables that are generated when PCRE is built are used.
+</P>
+<P>
+The function <b>pcre_fullinfo()</b> is used to find out information about a
+compiled pattern. The function <b>pcre_version()</b> returns a pointer to a
+string containing the version of PCRE and its date of release.
+</P>
+<P>
+The function <b>pcre_refcount()</b> maintains a reference count in a data block
+containing a compiled pattern. This is provided for the benefit of
+object-oriented applications.
+</P>
+<P>
+The global variables <b>pcre_malloc</b> and <b>pcre_free</b> initially contain
+the entry points of the standard <b>malloc()</b> and <b>free()</b> functions,
+respectively. PCRE calls the memory management functions via these variables,
+so a calling program can replace them if it wishes to intercept the calls. This
+should be done before calling any PCRE functions.
+</P>
+<P>
+The global variables <b>pcre_stack_malloc</b> and <b>pcre_stack_free</b> are also
+indirections to memory management functions. These special functions are used
+only when PCRE is compiled to use the heap for remembering data, instead of
+recursive function calls, when running the <b>pcre_exec()</b> function. See the
+<a href="pcrebuild.html"><b>pcrebuild</b></a>
+documentation for details of how to do this. It is a non-standard way of
+building PCRE, for use in environments that have limited stacks. Because of the
+greater use of memory management, it runs more slowly. Separate functions are
+provided so that special-purpose external code can be used for this case. When
+used, these functions always allocate memory blocks of the same size. There is
+a discussion about PCRE's stack usage in the
+<a href="pcrestack.html"><b>pcrestack</b></a>
+documentation.
+</P>
+<P>
+The global variable <b>pcre_callout</b> initially contains NULL. It can be set
+by the caller to a "callout" function, which PCRE will then call at specified
+points during a matching operation. Details are given in the
+<a href="pcrecallout.html"><b>pcrecallout</b></a>
+documentation.
+</P>
+<P>
+The global variable <b>pcre_stack_guard</b> initially contains NULL. It can be
+set by the caller to a function that is called by PCRE whenever it starts
+to compile a parenthesized part of a pattern. When parentheses are nested, PCRE
+uses recursive function calls, which use up the system stack. This function is
+provided so that applications with restricted stacks can force a compilation
+error if the stack runs out. The function should return zero if all is well, or
+non-zero to force an error.
+<a name="newlines"></a></P>
+<br><a name="SEC7" href="#TOC1">NEWLINES</a><br>
+<P>
+PCRE supports five different conventions for indicating line breaks in
+strings: a single CR (carriage return) character, a single LF (linefeed)
+character, the two-character sequence CRLF, any of the three preceding, or any
+Unicode newline sequence. The Unicode newline sequences are the three just
+mentioned, plus the single characters VT (vertical tab, U+000B), FF (form feed,
+U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
+(paragraph separator, U+2029).
+</P>
+<P>
+Each of the first three conventions is used by at least one operating system as
+its standard newline sequence. When PCRE is built, a default can be specified.
+The default default is LF, which is the Unix standard. When PCRE is run, the
+default can be overridden, either when a pattern is compiled, or when it is
+matched.
+</P>
+<P>
+At compile time, the newline convention can be specified by the <i>options</i>
+argument of <b>pcre_compile()</b>, or it can be specified by special text at the
+start of the pattern itself; this overrides any other settings. See the
+<a href="pcrepattern.html"><b>pcrepattern</b></a>
+page for details of the special character sequences.
+</P>
+<P>
+In the PCRE documentation the word "newline" is used to mean "the character or
+pair of characters that indicate a line break". The choice of newline
+convention affects the handling of the dot, circumflex, and dollar
+metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
+recognized line ending sequence, the match position advancement for a
+non-anchored pattern. There is more detail about this in the
+<a href="#execoptions">section on <b>pcre_exec()</b> options</a>
+below.
+</P>
+<P>
+The choice of newline convention does not affect the interpretation of
+the \n or \r escape sequences, nor does it affect what \R matches, which is
+controlled in a similar way, but by separate options.
+</P>
+<br><a name="SEC8" href="#TOC1">MULTITHREADING</a><br>
+<P>
+The PCRE functions can be used in multi-threading applications, with the
+proviso that the memory management functions pointed to by <b>pcre_malloc</b>,
+<b>pcre_free</b>, <b>pcre_stack_malloc</b>, and <b>pcre_stack_free</b>, and the
+callout and stack-checking functions pointed to by <b>pcre_callout</b> and
+<b>pcre_stack_guard</b>, are shared by all threads.
+</P>
+<P>
+The compiled form of a regular expression is not altered during matching, so
+the same compiled pattern can safely be used by several threads at once.
+</P>
+<P>
+If the just-in-time optimization feature is being used, it needs separate
+memory stack areas for each thread. See the
+<a href="pcrejit.html"><b>pcrejit</b></a>
+documentation for more details.
+</P>
+<br><a name="SEC9" href="#TOC1">SAVING PRECOMPILED PATTERNS FOR LATER USE</a><br>
+<P>
+The compiled form of a regular expression can be saved and re-used at a later
+time, possibly by a different program, and even on a host other than the one on
+which it was compiled. Details are given in the
+<a href="pcreprecompile.html"><b>pcreprecompile</b></a>
+documentation, which includes a description of the
+<b>pcre_pattern_to_host_byte_order()</b> function. However, compiling a regular
+expression with one version of PCRE for use with a different version is not
+guaranteed to work and may cause crashes.
+</P>
+<br><a name="SEC10" href="#TOC1">CHECKING BUILD-TIME OPTIONS</a><br>
+<P>
+<b>int pcre_config(int <i>what</i>, void *<i>where</i>);</b>
+</P>
+<P>
+The function <b>pcre_config()</b> makes it possible for a PCRE client to
+discover which optional features have been compiled into the PCRE library. The
+<a href="pcrebuild.html"><b>pcrebuild</b></a>
+documentation has more details about these optional features.
+</P>
+<P>
+The first argument for <b>pcre_config()</b> is an integer, specifying which
+information is required; the second argument is a pointer to a variable into
+which the information is placed. The returned value is zero on success, or the
+negative error code PCRE_ERROR_BADOPTION if the value in the first argument is
+not recognized. The following information is available:
+<pre>
+ PCRE_CONFIG_UTF8
+</pre>
+The output is an integer that is set to one if UTF-8 support is available;
+otherwise it is set to zero. This value should normally be given to the 8-bit
+version of this function, <b>pcre_config()</b>. If it is given to the 16-bit
+or 32-bit version of this function, the result is PCRE_ERROR_BADOPTION.
+<pre>
+ PCRE_CONFIG_UTF16
+</pre>
+The output is an integer that is set to one if UTF-16 support is available;
+otherwise it is set to zero. This value should normally be given to the 16-bit
+version of this function, <b>pcre16_config()</b>. If it is given to the 8-bit
+or 32-bit version of this function, the result is PCRE_ERROR_BADOPTION.
+<pre>
+ PCRE_CONFIG_UTF32
+</pre>
+The output is an integer that is set to one if UTF-32 support is available;
+otherwise it is set to zero. This value should normally be given to the 32-bit
+version of this function, <b>pcre32_config()</b>. If it is given to the 8-bit
+or 16-bit version of this function, the result is PCRE_ERROR_BADOPTION.
+<pre>
+ PCRE_CONFIG_UNICODE_PROPERTIES
+</pre>
+The output is an integer that is set to one if support for Unicode character
+properties is available; otherwise it is set to zero.
+<pre>
+ PCRE_CONFIG_JIT
+</pre>
+The output is an integer that is set to one if support for just-in-time
+compiling is available; otherwise it is set to zero.
+<pre>
+ PCRE_CONFIG_JITTARGET
+</pre>
+The output is a pointer to a zero-terminated "const char *" string. If JIT
+support is available, the string contains the name of the architecture for
+which the JIT compiler is configured, for example "x86 32bit (little endian +
+unaligned)". If JIT support is not available, the result is NULL.
+<pre>
+ PCRE_CONFIG_NEWLINE
+</pre>
+The output is an integer whose value specifies the default character sequence
+that is recognized as meaning "newline". The values that are supported in
+ASCII/Unicode environments are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for
+ANYCRLF, and -1 for ANY. In EBCDIC environments, CR, ANYCRLF, and ANY yield the
+same values. However, the value for LF is normally 21, though some EBCDIC
+environments use 37. The corresponding values for CRLF are 3349 and 3365. The
+default should normally correspond to the standard sequence for your operating
+system.
+<pre>
+ PCRE_CONFIG_BSR
+</pre>
+The output is an integer whose value indicates what character sequences the \R
+escape sequence matches by default. A value of 0 means that \R matches any
+Unicode line ending sequence; a value of 1 means that \R matches only CR, LF,
+or CRLF. The default can be overridden when a pattern is compiled or matched.
+<pre>
+ PCRE_CONFIG_LINK_SIZE
+</pre>
+The output is an integer that contains the number of bytes used for internal
+linkage in compiled regular expressions. For the 8-bit library, the value can
+be 2, 3, or 4. For the 16-bit library, the value is either 2 or 4 and is still
+a number of bytes. For the 32-bit library, the value is either 2 or 4 and is
+still a number of bytes. The default value of 2 is sufficient for all but the
+most massive patterns, since it allows the compiled pattern to be up to 64K in
+size. Larger values allow larger regular expressions to be compiled, at the
+expense of slower matching.
+<pre>
+ PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
+</pre>
+The output is an integer that contains the threshold above which the POSIX
+interface uses <b>malloc()</b> for output vectors. Further details are given in
+the
+<a href="pcreposix.html"><b>pcreposix</b></a>
+documentation.
+<pre>
+ PCRE_CONFIG_PARENS_LIMIT
+</pre>
+The output is a long integer that gives the maximum depth of nesting of
+parentheses (of any kind) in a pattern. This limit is imposed to cap the amount
+of system stack used when a pattern is compiled. It is specified when PCRE is
+built; the default is 250. This limit does not take into account the stack that
+may already be used by the calling application. For finer control over
+compilation stack usage, you can set a pointer to an external checking function
+in <b>pcre_stack_guard</b>.
+<pre>
+ PCRE_CONFIG_MATCH_LIMIT
+</pre>
+The output is a long integer that gives the default limit for the number of
+internal matching function calls in a <b>pcre_exec()</b> execution. Further
+details are given with <b>pcre_exec()</b> below.
+<pre>
+ PCRE_CONFIG_MATCH_LIMIT_RECURSION
+</pre>
+The output is a long integer that gives the default limit for the depth of
+recursion when calling the internal matching function in a <b>pcre_exec()</b>
+execution. Further details are given with <b>pcre_exec()</b> below.
+<pre>
+ PCRE_CONFIG_STACKRECURSE
+</pre>
+The output is an integer that is set to one if internal recursion when running
+<b>pcre_exec()</b> is implemented by recursive function calls that use the stack
+to remember their state. This is the usual way that PCRE is compiled. The
+output is zero if PCRE was compiled to use blocks of data on the heap instead
+of recursive function calls. In this case, <b>pcre_stack_malloc</b> and
+<b>pcre_stack_free</b> are called to manage memory blocks on the heap, thus
+avoiding the use of the stack.
+</P>
+<br><a name="SEC11" href="#TOC1">COMPILING A PATTERN</a><br>
+<P>
+<b>pcre *pcre_compile(const char *<i>pattern</i>, int <i>options</i>,</b>
+<b> const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
+<b> const unsigned char *<i>tableptr</i>);</b>
+<br>
+<br>
+<b>pcre *pcre_compile2(const char *<i>pattern</i>, int <i>options</i>,</b>
+<b> int *<i>errorcodeptr</i>,</b>
+<b> const char **<i>errptr</i>, int *<i>erroffset</i>,</b>
+<b> const unsigned char *<i>tableptr</i>);</b>
+</P>
+<P>
+Either of the functions <b>pcre_compile()</b> or <b>pcre_compile2()</b> can be
+called to compile a pattern into an internal form. The only difference between
+the two interfaces is that <b>pcre_compile2()</b> has an additional argument,
+<i>errorcodeptr</i>, via which a numerical error code can be returned. To avoid
+too much repetition, we refer just to <b>pcre_compile()</b> below, but the
+information applies equally to <b>pcre_compile2()</b>.
+</P>
+<P>
+The pattern is a C string terminated by a binary zero, and is passed in the
+<i>pattern</i> argument. A pointer to a single block of memory that is obtained
+via <b>pcre_malloc</b> is returned. This contains the compiled code and related
+data. The <b>pcre</b> type is defined for the returned block; this is a typedef
+for a structure whose contents are not externally defined. It is up to the
+caller to free the memory (via <b>pcre_free</b>) when it is no longer required.
+</P>
+<P>
+Although the compiled code of a PCRE regex is relocatable, that is, it does not
+depend on memory location, the complete <b>pcre</b> data block is not
+fully relocatable, because it may contain a copy of the <i>tableptr</i>
+argument, which is an address (see below).
+</P>
+<P>
+The <i>options</i> argument contains various bit settings that affect the
+compilation. It should be zero if no options are required. The available
+options are described below. Some of them (in particular, those that are
+compatible with Perl, but some others as well) can also be set and unset from
+within the pattern (see the detailed description in the
+<a href="pcrepattern.html"><b>pcrepattern</b></a>
+documentation). For those options that can be different in different parts of
+the pattern, the contents of the <i>options</i> argument specifies their
+settings at the start of compilation and execution. The PCRE_ANCHORED,
+PCRE_BSR_<i>xxx</i>, PCRE_NEWLINE_<i>xxx</i>, PCRE_NO_UTF8_CHECK, and
+PCRE_NO_START_OPTIMIZE options can be set at the time of matching as well as at
+compile time.
+</P>
+<P>
+If <i>errptr</i> is NULL, <b>pcre_compile()</b> returns NULL immediately.
+Otherwise, if compilation of a pattern fails, <b>pcre_compile()</b> returns
+NULL, and sets the variable pointed to by <i>errptr</i> to point to a textual
+error message. This is a static string that is part of the library. You must
+not try to free it. Normally, the offset from the start of the pattern to the
+data unit that was being processed when the error was discovered is placed in
+the variable pointed to by <i>erroffset</i>, which must not be NULL (if it is,
+an immediate error is given). However, for an invalid UTF-8 or UTF-16 string,
+the offset is that of the first data unit of the failing character.
+</P>
+<P>
+Some errors are not detected until the whole pattern has been scanned; in these
+cases, the offset passed back is the length of the pattern. Note that the
+offset is in data units, not characters, even in a UTF mode. It may sometimes
+point into the middle of a UTF-8 or UTF-16 character.
+</P>
+<P>
+If <b>pcre_compile2()</b> is used instead of <b>pcre_compile()</b>, and the
+<i>errorcodeptr</i> argument is not NULL, a non-zero error code number is
+returned via this argument in the event of an error. This is in addition to the
+textual error message. Error codes and messages are listed below.
+</P>
+<P>
+If the final argument, <i>tableptr</i>, is NULL, PCRE uses a default set of
+character tables that are built when PCRE is compiled, using the default C
+locale. Otherwise, <i>tableptr</i> must be an address that is the result of a
+call to <b>pcre_maketables()</b>. This value is stored with the compiled
+pattern, and used again by <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b> when the
+pattern is matched. For more discussion, see the section on locale support
+below.
+</P>
+<P>
+This code fragment shows a typical straightforward call to <b>pcre_compile()</b>:
+<pre>
+ pcre *re;
+ const char *error;
+ int erroffset;
+ re = pcre_compile(
+ "^A.*Z", /* the pattern */
+ 0, /* default options */
+ &error, /* for error message */
+ &erroffset, /* for error offset */
+ NULL); /* use default character tables */
+</pre>
+The following names for option bits are defined in the <b>pcre.h</b> header
+file:
+<pre>
+ PCRE_ANCHORED
+</pre>
+If this bit is set, the pattern is forced to be "anchored", that is, it is
+constrained to match only at the first matching point in the string that is
+being searched (the "subject string"). This effect can also be achieved by
+appropriate constructs in the pattern itself, which is the only way to do it in
+Perl.
+<pre>
+ PCRE_AUTO_CALLOUT
+</pre>
+If this bit is set, <b>pcre_compile()</b> automatically inserts callout items,
+all with number 255, before each pattern item. For discussion of the callout
+facility, see the
+<a href="pcrecallout.html"><b>pcrecallout</b></a>
+documentation.
+<pre>
+ PCRE_BSR_ANYCRLF
+ PCRE_BSR_UNICODE
+</pre>
+These options (which are mutually exclusive) control what the \R escape
+sequence matches. The choice is either to match only CR, LF, or CRLF, or to
+match any Unicode newline sequence. The default is specified when PCRE is
+built. It can be overridden from within the pattern, or by setting an option
+when a compiled pattern is matched.
+<pre>
+ PCRE_CASELESS
+</pre>
+If this bit is set, letters in the pattern match both upper and lower case
+letters. It is equivalent to Perl's /i option, and it can be changed within a
+pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
+concept of case for characters whose values are less than 128, so caseless
+matching is always possible. For characters with higher values, the concept of
+case is supported if PCRE is compiled with Unicode property support, but not
+otherwise. If you want to use caseless matching for characters 128 and above,
+you must ensure that PCRE is compiled with Unicode property support as well as
+with UTF-8 support.
+<pre>
+ PCRE_DOLLAR_ENDONLY
+</pre>
+If this bit is set, a dollar metacharacter in the pattern matches only at the
+end of the subject string. Without this option, a dollar also matches
+immediately before a newline at the end of the string (but not before any other
+newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
+There is no equivalent to this option in Perl, and no way to set it within a
+pattern.
+<pre>
+ PCRE_DOTALL
+</pre>
+If this bit is set, a dot metacharacter in the pattern matches a character of
+any value, including one that indicates a newline. However, it only ever
+matches one character, even if newlines are coded as CRLF. Without this option,
+a dot does not match when the current position is at a newline. This option is
+equivalent to Perl's /s option, and it can be changed within a pattern by a
+(?s) option setting. A negative class such as [^a] always matches newline
+characters, independent of the setting of this option.
+<pre>
+ PCRE_DUPNAMES
+</pre>
+If this bit is set, names used to identify capturing subpatterns need not be
+unique. This can be helpful for certain types of pattern when it is known that
+only one instance of the named subpattern can ever be matched. There are more
+details of named subpatterns below; see also the
+<a href="pcrepattern.html"><b>pcrepattern</b></a>
+documentation.
+<pre>
+ PCRE_EXTENDED
+</pre>
+If this bit is set, most white space characters in the pattern are totally
+ignored except when escaped or inside a character class. However, white space
+is not allowed within sequences such as (?&#62; that introduce various
+parenthesized subpatterns, nor within a numerical quantifier such as {1,3}.
+However, ignorable white space is permitted between an item and a following
+quantifier and between a quantifier and a following + that indicates
+possessiveness.
+</P>
+<P>
+White space did not used to include the VT character (code 11), because Perl
+did not treat this character as white space. However, Perl changed at release
+5.18, so PCRE followed at release 8.34, and VT is now treated as white space.
+</P>
+<P>
+PCRE_EXTENDED also causes characters between an unescaped # outside a character
+class and the next newline, inclusive, to be ignored. PCRE_EXTENDED is
+equivalent to Perl's /x option, and it can be changed within a pattern by a
+(?x) option setting.
+</P>
+<P>
+Which characters are interpreted as newlines is controlled by the options
+passed to <b>pcre_compile()</b> or by a special sequence at the start of the
+pattern, as described in the section entitled
+<a href="pcrepattern.html#newlines">"Newline conventions"</a>
+in the <b>pcrepattern</b> documentation. Note that the end of this type of
+comment is a literal newline sequence in the pattern; escape sequences that
+happen to represent a newline do not count.
+</P>
+<P>
+This option makes it possible to include comments inside complicated patterns.
+Note, however, that this applies only to data characters. White space characters
+may never appear within special character sequences in a pattern, for example
+within the sequence (?( that introduces a conditional subpattern.
+<pre>
+ PCRE_EXTRA
+</pre>
+This option was invented in order to turn on additional functionality of PCRE
+that is incompatible with Perl, but it is currently of very little use. When
+set, any backslash in a pattern that is followed by a letter that has no
+special meaning causes an error, thus reserving these combinations for future
+expansion. By default, as in Perl, a backslash followed by a letter with no
+special meaning is treated as a literal. (Perl can, however, be persuaded to
+give an error for this, by running it with the -w option.) There are at present
+no other features controlled by this option. It can also be set by a (?X)
+option setting within a pattern.
+<pre>
+ PCRE_FIRSTLINE
+</pre>
+If this option is set, an unanchored pattern is required to match before or at
+the first newline in the subject string, though the matched text may continue
+over the newline.
+<pre>
+ PCRE_JAVASCRIPT_COMPAT
+</pre>
+If this option is set, PCRE's behaviour is changed in some ways so that it is
+compatible with JavaScript rather than Perl. The changes are as follows:
+</P>
+<P>
+(1) A lone closing square bracket in a pattern causes a compile-time error,
+because this is illegal in JavaScript (by default it is treated as a data
+character). Thus, the pattern AB]CD becomes illegal when this option is set.
+</P>
+<P>
+(2) At run time, a back reference to an unset subpattern group matches an empty
+string (by default this causes the current matching alternative to fail). A
+pattern such as (\1)(a) succeeds when this option is set (assuming it can find
+an "a" in the subject), whereas it fails by default, for Perl compatibility.
+</P>
+<P>
+(3) \U matches an upper case "U" character; by default \U causes a compile
+time error (Perl uses \U to upper case subsequent characters).
+</P>
+<P>
+(4) \u matches a lower case "u" character unless it is followed by four
+hexadecimal digits, in which case the hexadecimal number defines the code point
+to match. By default, \u causes a compile time error (Perl uses it to upper
+case the following character).
+</P>
+<P>
+(5) \x matches a lower case "x" character unless it is followed by two
+hexadecimal digits, in which case the hexadecimal number defines the code point
+to match. By default, as in Perl, a hexadecimal number is always expected after
+\x, but it may have zero, one, or two digits (so, for example, \xz matches a
+binary zero character followed by z).
+<pre>
+ PCRE_MULTILINE
+</pre>
+By default, for the purposes of matching "start of line" and "end of line",
+PCRE treats the subject string as consisting of a single line of characters,
+even if it actually contains newlines. The "start of line" metacharacter (^)
+matches only at the start of the string, and the "end of line" metacharacter
+($) matches only at the end of the string, or before a terminating newline
+(except when PCRE_DOLLAR_ENDONLY is set). Note, however, that unless
+PCRE_DOTALL is set, the "any character" metacharacter (.) does not match at a
+newline. This behaviour (for ^, $, and dot) is the same as Perl.
+</P>
+<P>
+When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
+match immediately following or immediately before internal newlines in the
+subject string, respectively, as well as at the very start and end. This is
+equivalent to Perl's /m option, and it can be changed within a pattern by a
+(?m) option setting. If there are no newlines in a subject string, or no
+occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
+<pre>
+ PCRE_NEVER_UTF
+</pre>
+This option locks out interpretation of the pattern as UTF-8 (or UTF-16 or
+UTF-32 in the 16-bit and 32-bit libraries). In particular, it prevents the
+creator of the pattern from switching to UTF interpretation by starting the
+pattern with (*UTF). This may be useful in applications that process patterns
+from external sources. The combination of PCRE_UTF8 and PCRE_NEVER_UTF also
+causes an error.
+<pre>
+ PCRE_NEWLINE_CR
+ PCRE_NEWLINE_LF
+ PCRE_NEWLINE_CRLF
+ PCRE_NEWLINE_ANYCRLF
+ PCRE_NEWLINE_ANY
+</pre>
+These options override the default newline definition that was chosen when PCRE
+was built. Setting the first or the second specifies that a newline is
+indicated by a single character (CR or LF, respectively). Setting
+PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
+CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
+preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
+that any Unicode newline sequence should be recognized.
+</P>
+<P>
+In an ASCII/Unicode environment, the Unicode newline sequences are the three
+just mentioned, plus the single characters VT (vertical tab, U+000B), FF (form
+feed, U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
+(paragraph separator, U+2029). For the 8-bit library, the last two are
+recognized only in UTF-8 mode.
+</P>
+<P>
+When PCRE is compiled to run in an EBCDIC (mainframe) environment, the code for
+CR is 0x0d, the same as ASCII. However, the character code for LF is normally
+0x15, though in some EBCDIC environments 0x25 is used. Whichever of these is
+not LF is made to correspond to Unicode's NEL character. EBCDIC codes are all
+less than 256. For more details, see the
+<a href="pcrebuild.html"><b>pcrebuild</b></a>
+documentation.
+</P>
+<P>
+The newline setting in the options word uses three bits that are treated
+as a number, giving eight possibilities. Currently only six are used (default
+plus the five values above). This means that if you set more than one newline
+option, the combination may or may not be sensible. For example,
+PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to PCRE_NEWLINE_CRLF, but
+other combinations may yield unused numbers and cause an error.
+</P>
+<P>
+The only time that a line break in a pattern is specially recognized when
+compiling is when PCRE_EXTENDED is set. CR and LF are white space characters,
+and so are ignored in this mode. Also, an unescaped # outside a character class
+indicates a comment that lasts until after the next line break sequence. In
+other circumstances, line break sequences in patterns are treated as literal
+data.
+</P>
+<P>
+The newline option that is set at compile time becomes the default that is used
+for <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, but it can be overridden.
+<pre>
+ PCRE_NO_AUTO_CAPTURE
+</pre>
+If this option is set, it disables the use of numbered capturing parentheses in
+the pattern. Any opening parenthesis that is not followed by ? behaves as if it
+were followed by ?: but named parentheses can still be used for capturing (and
+they acquire numbers in the usual way). There is no equivalent of this option
+in Perl.
+<pre>
+ PCRE_NO_AUTO_POSSESS
+</pre>
+If this option is set, it disables "auto-possessification". This is an
+optimization that, for example, turns a+b into a++b in order to avoid
+backtracks into a+ that can never be successful. However, if callouts are in
+use, auto-possessification means that some of them are never taken. You can set
+this option if you want the matching functions to do a full unoptimized search
+and run all the callouts, but it is mainly provided for testing purposes.
+<pre>
+ PCRE_NO_START_OPTIMIZE
+</pre>
+This is an option that acts at matching time; that is, it is really an option
+for <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>. If it is set at compile time,
+it is remembered with the compiled pattern and assumed at matching time. This
+is necessary if you want to use JIT execution, because the JIT compiler needs
+to know whether or not this option is set. For details see the discussion of
+PCRE_NO_START_OPTIMIZE
+<a href="#execoptions">below.</a>
+<pre>
+ PCRE_UCP
+</pre>
+This option changes the way PCRE processes \B, \b, \D, \d, \S, \s, \W,
+\w, and some of the POSIX character classes. By default, only ASCII characters
+are recognized, but if PCRE_UCP is set, Unicode properties are used instead to
+classify characters. More details are given in the section on
+<a href="pcre.html#genericchartypes">generic character types</a>
+in the
+<a href="pcrepattern.html"><b>pcrepattern</b></a>
+page. If you set PCRE_UCP, matching one of the items it affects takes much
+longer. The option is available only if PCRE has been compiled with Unicode
+property support.
+<pre>
+ PCRE_UNGREEDY
+</pre>
+This option inverts the "greediness" of the quantifiers so that they are not
+greedy by default, but become greedy if followed by "?". It is not compatible
+with Perl. It can also be set by a (?U) option setting within the pattern.
+<pre>
+ PCRE_UTF8
+</pre>
+This option causes PCRE to regard both the pattern and the subject as strings
+of UTF-8 characters instead of single-byte strings. However, it is available
+only when PCRE is built to include UTF support. If not, the use of this option
+provokes an error. Details of how this option changes the behaviour of PCRE are
+given in the
+<a href="pcreunicode.html"><b>pcreunicode</b></a>
+page.
+<pre>
+ PCRE_NO_UTF8_CHECK
+</pre>
+When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
+automatically checked. There is a discussion about the
+<a href="pcreunicode.html#utf8strings">validity of UTF-8 strings</a>
+in the
+<a href="pcreunicode.html"><b>pcreunicode</b></a>
+page. If an invalid UTF-8 sequence is found, <b>pcre_compile()</b> returns an
+error. If you already know that your pattern is valid, and you want to skip
+this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK option.
+When it is set, the effect of passing an invalid UTF-8 string as a pattern is
+undefined. It may cause your program to crash or loop. Note that this option
+can also be passed to <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>, to suppress
+the validity checking of subject strings only. If the same string is being
+matched many times, the option can be safely set for the second and subsequent
+matchings to improve performance.
+</P>
+<br><a name="SEC12" href="#TOC1">COMPILATION ERROR CODES</a><br>
+<P>
+The following table lists the error codes than may be returned by
+<b>pcre_compile2()</b>, along with the error messages that may be returned by
+both compiling functions. Note that error messages are always 8-bit ASCII
+strings, even in 16-bit or 32-bit mode. As PCRE has developed, some error codes
+have fallen out of use. To avoid confusion, they have not been re-used.
+<pre>
+ 0 no error
+ 1 \ at end of pattern
+ 2 \c at end of pattern
+ 3 unrecognized character follows \
+ 4 numbers out of order in {} quantifier
+ 5 number too big in {} quantifier
+ 6 missing terminating ] for character class
+ 7 invalid escape sequence in character class
+ 8 range out of order in character class
+ 9 nothing to repeat
+ 10 [this code is not in use]
+ 11 internal error: unexpected repeat
+ 12 unrecognized character after (? or (?-
+ 13 POSIX named classes are supported only within a class
+ 14 missing )
+ 15 reference to non-existent subpattern
+ 16 erroffset passed as NULL
+ 17 unknown option bit(s) set
+ 18 missing ) after comment
+ 19 [this code is not in use]
+ 20 regular expression is too large
+ 21 failed to get memory
+ 22 unmatched parentheses
+ 23 internal error: code overflow
+ 24 unrecognized character after (?&#60;
+ 25 lookbehind assertion is not fixed length
+ 26 malformed number or name after (?(
+ 27 conditional group contains more than two branches
+ 28 assertion expected after (?(
+ 29 (?R or (?[+-]digits must be followed by )
+ 30 unknown POSIX class name
+ 31 POSIX collating elements are not supported
+ 32 this version of PCRE is compiled without UTF support
+ 33 [this code is not in use]
+ 34 character value in \x{} or \o{} is too large
+ 35 invalid condition (?(0)
+ 36 \C not allowed in lookbehind assertion
+ 37 PCRE does not support \L, \l, \N{name}, \U, or \u
+ 38 number after (?C is &#62; 255
+ 39 closing ) for (?C expected
+ 40 recursive call could loop indefinitely
+ 41 unrecognized character after (?P
+ 42 syntax error in subpattern name (missing terminator)
+ 43 two named subpatterns have the same name
+ 44 invalid UTF-8 string (specifically UTF-8)
+ 45 support for \P, \p, and \X has not been compiled
+ 46 malformed \P or \p sequence
+ 47 unknown property name after \P or \p
+ 48 subpattern name is too long (maximum 32 characters)
+ 49 too many named subpatterns (maximum 10000)
+ 50 [this code is not in use]
+ 51 octal value is greater than \377 in 8-bit non-UTF-8 mode
+ 52 internal error: overran compiling workspace
+ 53 internal error: previously-checked referenced subpattern
+ not found
+ 54 DEFINE group contains more than one branch
+ 55 repeating a DEFINE group is not allowed
+ 56 inconsistent NEWLINE options
+ 57 \g is not followed by a braced, angle-bracketed, or quoted
+ name/number or by a plain number
+ 58 a numbered reference must not be zero
+ 59 an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
+ 60 (*VERB) not recognized or malformed
+ 61 number is too big
+ 62 subpattern name expected
+ 63 digit expected after (?+
+ 64 ] is an invalid data character in JavaScript compatibility mode
+ 65 different names for subpatterns of the same number are
+ not allowed
+ 66 (*MARK) must have an argument
+ 67 this version of PCRE is not compiled with Unicode property
+ support
+ 68 \c must be followed by an ASCII character
+ 69 \k is not followed by a braced, angle-bracketed, or quoted name
+ 70 internal error: unknown opcode in find_fixedlength()
+ 71 \N is not supported in a class
+ 72 too many forward references
+ 73 disallowed Unicode code point (&#62;= 0xd800 && &#60;= 0xdfff)
+ 74 invalid UTF-16 string (specifically UTF-16)
+ 75 name is too long in (*MARK), (*PRUNE), (*SKIP), or (*THEN)
+ 76 character value in \u.... sequence is too large
+ 77 invalid UTF-32 string (specifically UTF-32)
+ 78 setting UTF is disabled by the application
+ 79 non-hex character in \x{} (closing brace missing?)
+ 80 non-octal character in \o{} (closing brace missing?)
+ 81 missing opening brace after \o
+ 82 parentheses are too deeply nested
+ 83 invalid range in character class
+ 84 group name must start with a non-digit
+ 85 parentheses are too deeply nested (stack check)
+</pre>
+The numbers 32 and 10000 in errors 48 and 49 are defaults; different values may
+be used if the limits were changed when PCRE was built.
+<a name="studyingapattern"></a></P>
+<br><a name="SEC13" href="#TOC1">STUDYING A PATTERN</a><br>
+<P>
+<b>pcre_extra *pcre_study(const pcre *<i>code</i>, int <i>options</i>,</b>
+<b> const char **<i>errptr</i>);</b>
+</P>
+<P>
+If a compiled pattern is going to be used several times, it is worth spending
+more time analyzing it in order to speed up the time taken for matching. The
+function <b>pcre_study()</b> takes a pointer to a compiled pattern as its first
+argument. If studying the pattern produces additional information that will
+help speed up matching, <b>pcre_study()</b> returns a pointer to a
+<b>pcre_extra</b> block, in which the <i>study_data</i> field points to the
+results of the study.
+</P>
+<P>
+The returned value from <b>pcre_study()</b> can be passed directly to
+<b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>. However, a <b>pcre_extra</b> block
+also contains other fields that can be set by the caller before the block is
+passed; these are described
+<a href="#extradata">below</a>
+in the section on matching a pattern.
+</P>
+<P>
+If studying the pattern does not produce any useful information,
+<b>pcre_study()</b> returns NULL by default. In that circumstance, if the
+calling program wants to pass any of the other fields to <b>pcre_exec()</b> or
+<b>pcre_dfa_exec()</b>, it must set up its own <b>pcre_extra</b> block. However,
+if <b>pcre_study()</b> is called with the PCRE_STUDY_EXTRA_NEEDED option, it
+returns a <b>pcre_extra</b> block even if studying did not find any additional
+information. It may still return NULL, however, if an error occurs in
+<b>pcre_study()</b>.
+</P>
+<P>
+The second argument of <b>pcre_study()</b> contains option bits. There are three
+further options in addition to PCRE_STUDY_EXTRA_NEEDED:
+<pre>
+ PCRE_STUDY_JIT_COMPILE
+ PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
+ PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE
+</pre>
+If any of these are set, and the just-in-time compiler is available, the
+pattern is further compiled into machine code that executes much faster than
+the <b>pcre_exec()</b> interpretive matching function. If the just-in-time
+compiler is not available, these options are ignored. All undefined bits in the
+<i>options</i> argument must be zero.
+</P>
+<P>
+JIT compilation is a heavyweight optimization. It can take some time for
+patterns to be analyzed, and for one-off matches and simple patterns the
+benefit of faster execution might be offset by a much slower study time.
+Not all patterns can be optimized by the JIT compiler. For those that cannot be
+handled, matching automatically falls back to the <b>pcre_exec()</b>
+interpreter. For more details, see the
+<a href="pcrejit.html"><b>pcrejit</b></a>
+documentation.
+</P>
+<P>
+The third argument for <b>pcre_study()</b> is a pointer for an error message. If
+studying succeeds (even if no data is returned), the variable it points to is
+set to NULL. Otherwise it is set to point to a textual error message. This is a
+static string that is part of the library. You must not try to free it. You
+should test the error pointer for NULL after calling <b>pcre_study()</b>, to be
+sure that it has run successfully.
+</P>
+<P>
+When you are finished with a pattern, you can free the memory used for the
+study data by calling <b>pcre_free_study()</b>. This function was added to the
+API for release 8.20. For earlier versions, the memory could be freed with
+<b>pcre_free()</b>, just like the pattern itself. This will still work in cases
+where JIT optimization is not used, but it is advisable to change to the new
+function when convenient.
+</P>
+<P>
+This is a typical way in which <b>pcre_study</b>() is used (except that in a
+real application there should be tests for errors):
+<pre>
+ int rc;
+ pcre *re;
+ pcre_extra *sd;
+ re = pcre_compile("pattern", 0, &error, &erroroffset, NULL);
+ sd = pcre_study(
+ re, /* result of pcre_compile() */
+ 0, /* no options */
+ &error); /* set to NULL or points to a message */
+ rc = pcre_exec( /* see below for details of pcre_exec() options */
+ re, sd, "subject", 7, 0, 0, ovector, 30);
+ ...
+ pcre_free_study(sd);
+ pcre_free(re);
+</pre>
+Studying a pattern does two things: first, a lower bound for the length of
+subject string that is needed to match the pattern is computed. This does not
+mean that there are any strings of that length that match, but it does
+guarantee that no shorter strings match. The value is used to avoid wasting
+time by trying to match strings that are shorter than the lower bound. You can
+find out the value in a calling program via the <b>pcre_fullinfo()</b> function.
+</P>
+<P>
+Studying a pattern is also useful for non-anchored patterns that do not have a
+single fixed starting character. A bitmap of possible starting bytes is
+created. This speeds up finding a position in the subject at which to start
+matching. (In 16-bit mode, the bitmap is used for 16-bit values less than 256.
+In 32-bit mode, the bitmap is used for 32-bit values less than 256.)
+</P>
+<P>
+These two optimizations apply to both <b>pcre_exec()</b> and
+<b>pcre_dfa_exec()</b>, and the information is also used by the JIT compiler.
+The optimizations can be disabled by setting the PCRE_NO_START_OPTIMIZE option.
+You might want to do this if your pattern contains callouts or (*MARK) and you
+want to make use of these facilities in cases where matching fails.
+</P>
+<P>
+PCRE_NO_START_OPTIMIZE can be specified at either compile time or execution
+time. However, if PCRE_NO_START_OPTIMIZE is passed to <b>pcre_exec()</b>, (that
+is, after any JIT compilation has happened) JIT execution is disabled. For JIT
+execution to work with PCRE_NO_START_OPTIMIZE, the option must be set at
+compile time.
+</P>
+<P>
+There is a longer discussion of PCRE_NO_START_OPTIMIZE
+<a href="#execoptions">below.</a>
+<a name="localesupport"></a></P>
+<br><a name="SEC14" href="#TOC1">LOCALE SUPPORT</a><br>
+<P>
+PCRE handles caseless matching, and determines whether characters are letters,
+digits, or whatever, by reference to a set of tables, indexed by character
+code point. When running in UTF-8 mode, or in the 16- or 32-bit libraries, this
+applies only to characters with code points less than 256. By default,
+higher-valued code points never match escapes such as \w or \d. However, if
+PCRE is built with Unicode property support, all characters can be tested with
+\p and \P, or, alternatively, the PCRE_UCP option can be set when a pattern
+is compiled; this causes \w and friends to use Unicode property support
+instead of the built-in tables.
+</P>
+<P>
+The use of locales with Unicode is discouraged. If you are handling characters
+with code points greater than 128, you should either use Unicode support, or
+use locales, but not try to mix the two.
+</P>
+<P>
+PCRE contains an internal set of tables that are used when the final argument
+of <b>pcre_compile()</b> is NULL. These are sufficient for many applications.
+Normally, the internal tables recognize only ASCII characters. However, when
+PCRE is built, it is possible to cause the internal tables to be rebuilt in the
+default "C" locale of the local system, which may cause them to be different.
+</P>
+<P>
+The internal tables can always be overridden by tables supplied by the
+application that calls PCRE. These may be created in a different locale from
+the default. As more and more applications change to using Unicode, the need
+for this locale support is expected to die away.
+</P>
+<P>
+External tables are built by calling the <b>pcre_maketables()</b> function,
+which has no arguments, in the relevant locale. The result can then be passed
+to <b>pcre_compile()</b> as often as necessary. For example, to build and use
+tables that are appropriate for the French locale (where accented characters
+with values greater than 128 are treated as letters), the following code could
+be used:
+<pre>
+ setlocale(LC_CTYPE, "fr_FR");
+ tables = pcre_maketables();
+ re = pcre_compile(..., tables);
+</pre>
+The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
+are using Windows, the name for the French locale is "french".
+</P>
+<P>
+When <b>pcre_maketables()</b> runs, the tables are built in memory that is
+obtained via <b>pcre_malloc</b>. It is the caller's responsibility to ensure
+that the memory containing the tables remains available for as long as it is
+needed.
+</P>
+<P>
+The pointer that is passed to <b>pcre_compile()</b> is saved with the compiled
+pattern, and the same tables are used via this pointer by <b>pcre_study()</b>
+and also by <b>pcre_exec()</b> and <b>pcre_dfa_exec()</b>. Thus, for any single
+pattern, compilation, studying and matching all happen in the same locale, but
+different patterns can be processed in different locales.
+</P>
+<P>
+It is possible to pass a table pointer or NULL (indicating the use of the
+internal tables) to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> (see the
+discussion below in the section on matching a pattern). This facility is
+provided for use with pre-compiled patterns that have been saved and reloaded.
+Character tables are not saved with patterns, so if a non-standard table was
+used at compile time, it must be provided again when the reloaded pattern is
+matched. Attempting to use this facility to match a pattern in a different
+locale from the one in which it was compiled is likely to lead to anomalous
+(usually incorrect) results.
+<a name="infoaboutpattern"></a></P>
+<br><a name="SEC15" href="#TOC1">INFORMATION ABOUT A PATTERN</a><br>
+<P>
+<b>int pcre_fullinfo(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
+<b> int <i>what</i>, void *<i>where</i>);</b>
+</P>
+<P>
+The <b>pcre_fullinfo()</b> function returns information about a compiled
+pattern. It replaces the <b>pcre_info()</b> function, which was removed from the
+library at version 8.30, after more than 10 years of obsolescence.
+</P>
+<P>
+The first argument for <b>pcre_fullinfo()</b> is a pointer to the compiled
+pattern. The second argument is the result of <b>pcre_study()</b>, or NULL if
+the pattern was not studied. The third argument specifies which piece of
+information is required, and the fourth argument is a pointer to a variable
+to receive the data. The yield of the function is zero for success, or one of
+the following negative numbers:
+<pre>
+ PCRE_ERROR_NULL the argument <i>code</i> was NULL
+ the argument <i>where</i> was NULL
+ PCRE_ERROR_BADMAGIC the "magic number" was not found
+ PCRE_ERROR_BADENDIANNESS the pattern was compiled with different
+ endianness
+ PCRE_ERROR_BADOPTION the value of <i>what</i> was invalid
+ PCRE_ERROR_UNSET the requested field is not set
+</pre>
+The "magic number" is placed at the start of each compiled pattern as an simple
+check against passing an arbitrary memory pointer. The endianness error can
+occur if a compiled pattern is saved and reloaded on a different host. Here is
+a typical call of <b>pcre_fullinfo()</b>, to obtain the length of the compiled
+pattern:
+<pre>
+ int rc;
+ size_t length;
+ rc = pcre_fullinfo(
+ re, /* result of pcre_compile() */
+ sd, /* result of pcre_study(), or NULL */
+ PCRE_INFO_SIZE, /* what is required */
+ &length); /* where to put the data */
+</pre>
+The possible values for the third argument are defined in <b>pcre.h</b>, and are
+as follows:
+<pre>
+ PCRE_INFO_BACKREFMAX
+</pre>
+Return the number of the highest back reference in the pattern. The fourth
+argument should point to an <b>int</b> variable. Zero is returned if there are
+no back references.
+<pre>
+ PCRE_INFO_CAPTURECOUNT
+</pre>
+Return the number of capturing subpatterns in the pattern. The fourth argument
+should point to an <b>int</b> variable.
+<pre>
+ PCRE_INFO_DEFAULT_TABLES
+</pre>
+Return a pointer to the internal default character tables within PCRE. The
+fourth argument should point to an <b>unsigned char *</b> variable. This
+information call is provided for internal use by the <b>pcre_study()</b>
+function. External callers can cause PCRE to use its internal tables by passing
+a NULL table pointer.
+<pre>
+ PCRE_INFO_FIRSTBYTE (deprecated)
+</pre>
+Return information about the first data unit of any matched string, for a
+non-anchored pattern. The name of this option refers to the 8-bit library,
+where data units are bytes. The fourth argument should point to an <b>int</b>
+variable. Negative values are used for special cases. However, this means that
+when the 32-bit library is in non-UTF-32 mode, the full 32-bit range of
+characters cannot be returned. For this reason, this value is deprecated; use
+PCRE_INFO_FIRSTCHARACTERFLAGS and PCRE_INFO_FIRSTCHARACTER instead.
+</P>
+<P>
+If there is a fixed first value, for example, the letter "c" from a pattern
+such as (cat|cow|coyote), its value is returned. In the 8-bit library, the
+value is always less than 256. In the 16-bit library the value can be up to
+0xffff. In the 32-bit library the value can be up to 0x10ffff.
+</P>
+<P>
+If there is no fixed first value, and if either
+<br>
+<br>
+(a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
+starts with "^", or
+<br>
+<br>
+(b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
+(if it were set, the pattern would be anchored),
+<br>
+<br>
+-1 is returned, indicating that the pattern matches only at the start of a
+subject string or after any newline within the string. Otherwise -2 is
+returned. For anchored patterns, -2 is returned.
+<pre>
+ PCRE_INFO_FIRSTCHARACTER
+</pre>
+Return the value of the first data unit (non-UTF character) of any matched
+string in the situation where PCRE_INFO_FIRSTCHARACTERFLAGS returns 1;
+otherwise return 0. The fourth argument should point to an <b>uint_t</b>
+variable.
+</P>
+<P>
+In the 8-bit library, the value is always less than 256. In the 16-bit library
+the value can be up to 0xffff. In the 32-bit library in UTF-32 mode the value
+can be up to 0x10ffff, and up to 0xffffffff when not using UTF-32 mode.
+<pre>
+ PCRE_INFO_FIRSTCHARACTERFLAGS
+</pre>
+Return information about the first data unit of any matched string, for a
+non-anchored pattern. The fourth argument should point to an <b>int</b>
+variable.
+</P>
+<P>
+If there is a fixed first value, for example, the letter "c" from a pattern
+such as (cat|cow|coyote), 1 is returned, and the character value can be
+retrieved using PCRE_INFO_FIRSTCHARACTER. If there is no fixed first value, and
+if either
+<br>
+<br>
+(a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
+starts with "^", or
+<br>
+<br>
+(b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
+(if it were set, the pattern would be anchored),
+<br>
+<br>
+2 is returned, indicating that the pattern matches only at the start of a
+subject string or after any newline within the string. Otherwise 0 is
+returned. For anchored patterns, 0 is returned.
+<pre>
+ PCRE_INFO_FIRSTTABLE
+</pre>
+If the pattern was studied, and this resulted in the construction of a 256-bit
+table indicating a fixed set of values for the first data unit in any matching
+string, a pointer to the table is returned. Otherwise NULL is returned. The
+fourth argument should point to an <b>unsigned char *</b> variable.
+<pre>
+ PCRE_INFO_HASCRORLF
+</pre>
+Return 1 if the pattern contains any explicit matches for CR or LF characters,
+otherwise 0. The fourth argument should point to an <b>int</b> variable. An
+explicit match is either a literal CR or LF character, or \r or \n.
+<pre>
+ PCRE_INFO_JCHANGED
+</pre>
+Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise
+0. The fourth argument should point to an <b>int</b> variable. (?J) and
+(?-J) set and unset the local PCRE_DUPNAMES option, respectively.
+<pre>
+ PCRE_INFO_JIT
+</pre>
+Return 1 if the pattern was studied with one of the JIT options, and
+just-in-time compiling was successful. The fourth argument should point to an
+<b>int</b> variable. A return value of 0 means that JIT support is not available
+in this version of PCRE, or that the pattern was not studied with a JIT option,
+or that the JIT compiler could not handle this particular pattern. See the
+<a href="pcrejit.html"><b>pcrejit</b></a>
+documentation for details of what can and cannot be handled.
+<pre>
+ PCRE_INFO_JITSIZE
+</pre>
+If the pattern was successfully studied with a JIT option, return the size of
+the JIT compiled code, otherwise return zero. The fourth argument should point
+to a <b>size_t</b> variable.
+<pre>
+ PCRE_INFO_LASTLITERAL
+</pre>
+Return the value of the rightmost literal data unit that must exist in any
+matched string, other than at its start, if such a value has been recorded. The
+fourth argument should point to an <b>int</b> variable. If there is no such
+value, -1 is returned. For anchored patterns, a last literal value is recorded
+only if it follows something of variable length. For example, for the pattern
+/^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value
+is -1.
+</P>
+<P>
+Since for the 32-bit library using the non-UTF-32 mode, this function is unable
+to return the full 32-bit range of characters, this value is deprecated;
+instead the PCRE_INFO_REQUIREDCHARFLAGS and PCRE_INFO_REQUIREDCHAR values should
+be used.
+<pre>
+ PCRE_INFO_MATCH_EMPTY
+</pre>
+Return 1 if the pattern can match an empty string, otherwise 0. The fourth
+argument should point to an <b>int</b> variable.
+<pre>
+ PCRE_INFO_MATCHLIMIT
+</pre>
+If the pattern set a match limit by including an item of the form
+(*LIMIT_MATCH=nnnn) at the start, the value is returned. The fourth argument
+should point to an unsigned 32-bit integer. If no such value has been set, the
+call to <b>pcre_fullinfo()</b> returns the error PCRE_ERROR_UNSET.
+<pre>
+ PCRE_INFO_MAXLOOKBEHIND
+</pre>
+Return the number of characters (NB not data units) in the longest lookbehind
+assertion in the pattern. This information is useful when doing multi-segment
+matching using the partial matching facilities. Note that the simple assertions
+\b and \B require a one-character lookbehind. \A also registers a
+one-character lookbehind, though it does not actually inspect the previous
+character. This is to ensure that at least one character from the old segment
+is retained when a new segment is processed. Otherwise, if there are no
+lookbehinds in the pattern, \A might match incorrectly at the start of a new
+segment.
+<pre>
+ PCRE_INFO_MINLENGTH
+</pre>
+If the pattern was studied and a minimum length for matching subject strings
+was computed, its value is returned. Otherwise the returned value is -1. The
+value is a number of characters, which in UTF mode may be different from the
+number of data units. The fourth argument should point to an <b>int</b>
+variable. A non-negative value is a lower bound to the length of any matching
+string. There may not be any strings of that length that do actually match, but
+every string that does match is at least that long.
+<pre>
+ PCRE_INFO_NAMECOUNT
+ PCRE_INFO_NAMEENTRYSIZE
+ PCRE_INFO_NAMETABLE
+</pre>
+PCRE supports the use of named as well as numbered capturing parentheses. The
+names are just an additional way of identifying the parentheses, which still
+acquire numbers. Several convenience functions such as
+<b>pcre_get_named_substring()</b> are provided for extracting captured
+substrings by name. It is also possible to extract the data directly, by first
+converting the name to a number in order to access the correct pointers in the
+output vector (described with <b>pcre_exec()</b> below). To do the conversion,
+you need to use the name-to-number map, which is described by these three
+values.
+</P>
+<P>
+The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
+the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
+entry; both of these return an <b>int</b> value. The entry size depends on the
+length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
+entry of the table. This is a pointer to <b>char</b> in the 8-bit library, where
+the first two bytes of each entry are the number of the capturing parenthesis,
+most significant byte first. In the 16-bit library, the pointer points to
+16-bit data units, the first of which contains the parenthesis number. In the
+32-bit library, the pointer points to 32-bit data units, the first of which
+contains the parenthesis number. The rest of the entry is the corresponding
+name, zero terminated.
+</P>
+<P>
+The names are in alphabetical order. If (?| is used to create multiple groups
+with the same number, as described in the
+<a href="pcrepattern.html#dupsubpatternnumber">section on duplicate subpattern numbers</a>
+in the
+<a href="pcrepattern.html"><b>pcrepattern</b></a>
+page, the groups may be given the same name, but there is only one entry in the
+table. Different names for groups of the same number are not permitted.
+Duplicate names for subpatterns with different numbers are permitted,
+but only if PCRE_DUPNAMES is set. They appear in the table in the order in
+which they were found in the pattern. In the absence of (?| this is the order
+of increasing number; when (?| is used this is not necessarily the case because
+later subpatterns may have lower numbers.
+</P>
+<P>
+As a simple example of the name/number table, consider the following pattern
+after compilation by the 8-bit library (assume PCRE_EXTENDED is set, so white
+space - including newlines - is ignored):
+<pre>
+ (?&#60;date&#62; (?&#60;year&#62;(\d\d)?\d\d) - (?&#60;month&#62;\d\d) - (?&#60;day&#62;\d\d) )
+</pre>
+There are four named subpatterns, so the table has four entries, and each entry
+in the table is eight bytes long. The table is as follows, with non-printing
+bytes shows in hexadecimal, and undefined bytes shown as ??:
+<pre>
+ 00 01 d a t e 00 ??
+ 00 05 d a y 00 ?? ??
+ 00 04 m o n t h 00
+ 00 02 y e a r 00 ??
+</pre>
+When writing code to extract data from named subpatterns using the
+name-to-number map, remember that the length of the entries is likely to be
+different for each compiled pattern.
+<pre>
+ PCRE_INFO_OKPARTIAL
+</pre>
+Return 1 if the pattern can be used for partial matching with
+<b>pcre_exec()</b>, otherwise 0. The fourth argument should point to an
+<b>int</b> variable. From release 8.00, this always returns 1, because the
+restrictions that previously applied to partial matching have been lifted. The
+<a href="pcrepartial.html"><b>pcrepartial</b></a>
+documentation gives details of partial matching.
+<pre>
+ PCRE_INFO_OPTIONS
+</pre>
+Return a copy of the options with which the pattern was compiled. The fourth
+argument should point to an <b>unsigned long int</b> variable. These option bits
+are those specified in the call to <b>pcre_compile()</b>, modified by any
+top-level option settings at the start of the pattern itself. In other words,
+they are the options that will be in force when matching starts. For example,
+if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
+result is PCRE_CASELESS, PCRE_MULTILINE, and PCRE_EXTENDED.
+</P>
+<P>
+A pattern is automatically anchored by PCRE if all of its top-level
+alternatives begin with one of the following:
+<pre>
+ ^ unless PCRE_MULTILINE is set
+ \A always
+ \G always
+ .* if PCRE_DOTALL is set and there are no back references to the subpattern in which .* appears
+</pre>
+For such patterns, the PCRE_ANCHORED bit is set in the options returned by
+<b>pcre_fullinfo()</b>.
+<pre>
+ PCRE_INFO_RECURSIONLIMIT
+</pre>
+If the pattern set a recursion limit by including an item of the form
+(*LIMIT_RECURSION=nnnn) at the start, the value is returned. The fourth
+argument should point to an unsigned 32-bit integer. If no such value has been
+set, the call to <b>pcre_fullinfo()</b> returns the error PCRE_ERROR_UNSET.
+<pre>
+ PCRE_INFO_SIZE
+</pre>
+Return the size of the compiled pattern in bytes (for all three libraries). The
+fourth argument should point to a <b>size_t</b> variable. This value does not
+include the size of the <b>pcre</b> structure that is returned by
+<b>pcre_compile()</b>. The value that is passed as the argument to
+<b>pcre_malloc()</b> when <b>pcre_compile()</b> is getting memory in which to
+place the compiled data is the value returned by this option plus the size of
+the <b>pcre</b> structure. Studying a compiled pattern, with or without JIT,
+does not alter the value returned by this option.
+<pre>
+ PCRE_INFO_STUDYSIZE
+</pre>
+Return the size in bytes (for all three libraries) of the data block pointed to
+by the <i>study_data</i> field in a <b>pcre_extra</b> block. If <b>pcre_extra</b>
+is NULL, or there is no study data, zero is returned. The fourth argument
+should point to a <b>size_t</b> variable. The <i>study_data</i> field is set by
+<b>pcre_study()</b> to record information that will speed up matching (see the
+section entitled
+<a href="#studyingapattern">"Studying a pattern"</a>
+above). The format of the <i>study_data</i> block is private, but its length
+is made available via this option so that it can be saved and restored (see the
+<a href="pcreprecompile.html"><b>pcreprecompile</b></a>
+documentation for details).
+<pre>
+ PCRE_INFO_REQUIREDCHARFLAGS
+</pre>
+Returns 1 if there is a rightmost literal data unit that must exist in any
+matched string, other than at its start. The fourth argument should point to
+an <b>int</b> variable. If there is no such value, 0 is returned. If returning
+1, the character value itself can be retrieved using PCRE_INFO_REQUIREDCHAR.
+</P>
+<P>
+For anchored patterns, a last literal value is recorded only if it follows
+something of variable length. For example, for the pattern /^a\d+z\d+/ the
+returned value 1 (with "z" returned from PCRE_INFO_REQUIREDCHAR), but for
+/^a\dz\d/ the returned value is 0.
+<pre>
+ PCRE_INFO_REQUIREDCHAR
+</pre>
+Return the value of the rightmost literal data unit that must exist in any
+matched string, other than at its start, if such a value has been recorded. The
+fourth argument should point to an <b>uint32_t</b> variable. If there is no such
+value, 0 is returned.
+</P>
+<br><a name="SEC16" href="#TOC1">REFERENCE COUNTS</a><br>
+<P>
+<b>int pcre_refcount(pcre *<i>code</i>, int <i>adjust</i>);</b>
+</P>
+<P>
+The <b>pcre_refcount()</b> function is used to maintain a reference count in the
+data block that contains a compiled pattern. It is provided for the benefit of
+applications that operate in an object-oriented manner, where different parts
+of the application may be using the same compiled pattern, but you want to free
+the block when they are all done.
+</P>
+<P>
+When a pattern is compiled, the reference count field is initialized to zero.
+It is changed only by calling this function, whose action is to add the
+<i>adjust</i> value (which may be positive or negative) to it. The yield of the
+function is the new value. However, the value of the count is constrained to
+lie between 0 and 65535, inclusive. If the new value is outside these limits,
+it is forced to the appropriate limit value.
+</P>
+<P>
+Except when it is zero, the reference count is not correctly preserved if a
+pattern is compiled on one host and then transferred to a host whose byte-order
+is different. (This seems a highly unlikely scenario.)
+</P>
+<br><a name="SEC17" href="#TOC1">MATCHING A PATTERN: THE TRADITIONAL FUNCTION</a><br>
+<P>
+<b>int pcre_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
+<b> const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
+<b> int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>);</b>
+</P>
+<P>
+The function <b>pcre_exec()</b> is called to match a subject string against a
+compiled pattern, which is passed in the <i>code</i> argument. If the
+pattern was studied, the result of the study should be passed in the
+<i>extra</i> argument. You can call <b>pcre_exec()</b> with the same <i>code</i>
+and <i>extra</i> arguments as many times as you like, in order to match
+different subject strings with the same pattern.
+</P>
+<P>
+This function is the main matching facility of the library, and it operates in
+a Perl-like manner. For specialist use there is also an alternative matching
+function, which is described
+<a href="#dfamatch">below</a>
+in the section about the <b>pcre_dfa_exec()</b> function.
+</P>
+<P>
+In most applications, the pattern will have been compiled (and optionally
+studied) in the same process that calls <b>pcre_exec()</b>. However, it is
+possible to save compiled patterns and study data, and then use them later
+in different processes, possibly even on different hosts. For a discussion
+about this, see the
+<a href="pcreprecompile.html"><b>pcreprecompile</b></a>
+documentation.
+</P>
+<P>
+Here is an example of a simple call to <b>pcre_exec()</b>:
+<pre>
+ int rc;
+ int ovector[30];
+ rc = pcre_exec(
+ re, /* result of pcre_compile() */
+ NULL, /* we didn't study the pattern */
+ "some string", /* the subject string */
+ 11, /* the length of the subject string */
+ 0, /* start at offset 0 in the subject */
+ 0, /* default options */
+ ovector, /* vector of integers for substring information */
+ 30); /* number of elements (NOT size in bytes) */
+<a name="extradata"></a></PRE>
+</P>
+<br><b>
+Extra data for <b>pcre_exec()</b>
+</b><br>
+<P>
+If the <i>extra</i> argument is not NULL, it must point to a <b>pcre_extra</b>
+data block. The <b>pcre_study()</b> function returns such a block (when it
+doesn't return NULL), but you can also create one for yourself, and pass
+additional information in it. The <b>pcre_extra</b> block contains the following
+fields (not necessarily in this order):
+<pre>
+ unsigned long int <i>flags</i>;
+ void *<i>study_data</i>;
+ void *<i>executable_jit</i>;
+ unsigned long int <i>match_limit</i>;
+ unsigned long int <i>match_limit_recursion</i>;
+ void *<i>callout_data</i>;
+ const unsigned char *<i>tables</i>;
+ unsigned char **<i>mark</i>;
+</pre>
+In the 16-bit version of this structure, the <i>mark</i> field has type
+"PCRE_UCHAR16 **".
+<br>
+<br>
+In the 32-bit version of this structure, the <i>mark</i> field has type
+"PCRE_UCHAR32 **".
+</P>
+<P>
+The <i>flags</i> field is used to specify which of the other fields are set. The
+flag bits are:
+<pre>
+ PCRE_EXTRA_CALLOUT_DATA
+ PCRE_EXTRA_EXECUTABLE_JIT
+ PCRE_EXTRA_MARK
+ PCRE_EXTRA_MATCH_LIMIT
+ PCRE_EXTRA_MATCH_LIMIT_RECURSION
+ PCRE_EXTRA_STUDY_DATA
+ PCRE_EXTRA_TABLES
+</pre>
+Other flag bits should be set to zero. The <i>study_data</i> field and sometimes
+the <i>executable_jit</i> field are set in the <b>pcre_extra</b> block that is
+returned by <b>pcre_study()</b>, together with the appropriate flag bits. You
+should not set these yourself, but you may add to the block by setting other
+fields and their corresponding flag bits.
+</P>
+<P>
+The <i>match_limit</i> field provides a means of preventing PCRE from using up a
+vast amount of resources when running patterns that are not going to match,
+but which have a very large number of possibilities in their search trees. The
+classic example is a pattern that uses nested unlimited repeats.
+</P>
+<P>
+Internally, <b>pcre_exec()</b> uses a function called <b>match()</b>, which it
+calls repeatedly (sometimes recursively). The limit set by <i>match_limit</i> is
+imposed on the number of times this function is called during a match, which
+has the effect of limiting the amount of backtracking that can take place. For
+patterns that are not anchored, the count restarts from zero for each position
+in the subject string.
+</P>
+<P>
+When <b>pcre_exec()</b> is called with a pattern that was successfully studied
+with a JIT option, the way that the matching is executed is entirely different.
+However, there is still the possibility of runaway matching that goes on for a
+very long time, and so the <i>match_limit</i> value is also used in this case
+(but in a different way) to limit how long the matching can continue.
+</P>
+<P>
+The default value for the limit can be set when PCRE is built; the default
+default is 10 million, which handles all but the most extreme cases. You can
+override the default by suppling <b>pcre_exec()</b> with a <b>pcre_extra</b>
+block in which <i>match_limit</i> is set, and PCRE_EXTRA_MATCH_LIMIT is set in
+the <i>flags</i> field. If the limit is exceeded, <b>pcre_exec()</b> returns
+PCRE_ERROR_MATCHLIMIT.
+</P>
+<P>
+A value for the match limit may also be supplied by an item at the start of a
+pattern of the form
+<pre>
+ (*LIMIT_MATCH=d)
+</pre>
+where d is a decimal number. However, such a setting is ignored unless d is
+less than the limit set by the caller of <b>pcre_exec()</b> or, if no such limit
+is set, less than the default.
+</P>
+<P>
+The <i>match_limit_recursion</i> field is similar to <i>match_limit</i>, but
+instead of limiting the total number of times that <b>match()</b> is called, it
+limits the depth of recursion. The recursion depth is a smaller number than the
+total number of calls, because not all calls to <b>match()</b> are recursive.
+This limit is of use only if it is set smaller than <i>match_limit</i>.
+</P>
+<P>
+Limiting the recursion depth limits the amount of machine stack that can be
+used, or, when PCRE has been compiled to use memory on the heap instead of the
+stack, the amount of heap memory that can be used. This limit is not relevant,
+and is ignored, when matching is done using JIT compiled code.
+</P>
+<P>
+The default value for <i>match_limit_recursion</i> can be set when PCRE is
+built; the default default is the same value as the default for
+<i>match_limit</i>. You can override the default by suppling <b>pcre_exec()</b>
+with a <b>pcre_extra</b> block in which <i>match_limit_recursion</i> is set, and
+PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the <i>flags</i> field. If the limit
+is exceeded, <b>pcre_exec()</b> returns PCRE_ERROR_RECURSIONLIMIT.
+</P>
+<P>
+A value for the recursion limit may also be supplied by an item at the start of
+a pattern of the form
+<pre>
+ (*LIMIT_RECURSION=d)
+</pre>
+where d is a decimal number. However, such a setting is ignored unless d is
+less than the limit set by the caller of <b>pcre_exec()</b> or, if no such limit
+is set, less than the default.
+</P>
+<P>
+The <i>callout_data</i> field is used in conjunction with the "callout" feature,
+and is described in the
+<a href="pcrecallout.html"><b>pcrecallout</b></a>
+documentation.
+</P>
+<P>
+The <i>tables</i> field is provided for use with patterns that have been
+pre-compiled using custom character tables, saved to disc or elsewhere, and
+then reloaded, because the tables that were used to compile a pattern are not
+saved with it. See the
+<a href="pcreprecompile.html"><b>pcreprecompile</b></a>
+documentation for a discussion of saving compiled patterns for later use. If
+NULL is passed using this mechanism, it forces PCRE's internal tables to be
+used.
+</P>
+<P>
+<b>Warning:</b> The tables that <b>pcre_exec()</b> uses must be the same as those
+that were used when the pattern was compiled. If this is not the case, the
+behaviour of <b>pcre_exec()</b> is undefined. Therefore, when a pattern is
+compiled and matched in the same process, this field should never be set. In
+this (the most common) case, the correct table pointer is automatically passed
+with the compiled pattern from <b>pcre_compile()</b> to <b>pcre_exec()</b>.
+</P>
+<P>
+If PCRE_EXTRA_MARK is set in the <i>flags</i> field, the <i>mark</i> field must
+be set to point to a suitable variable. If the pattern contains any
+backtracking control verbs such as (*MARK:NAME), and the execution ends up with
+a name to pass back, a pointer to the name string (zero terminated) is placed
+in the variable pointed to by the <i>mark</i> field. The names are within the
+compiled pattern; if you wish to retain such a name you must copy it before
+freeing the memory of a compiled pattern. If there is no name to pass back, the
+variable pointed to by the <i>mark</i> field is set to NULL. For details of the
+backtracking control verbs, see the section entitled
+<a href="pcrepattern#backtrackcontrol">"Backtracking control"</a>
+in the
+<a href="pcrepattern.html"><b>pcrepattern</b></a>
+documentation.
+<a name="execoptions"></a></P>
+<br><b>
+Option bits for <b>pcre_exec()</b>
+</b><br>
+<P>
+The unused bits of the <i>options</i> argument for <b>pcre_exec()</b> must be
+zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
+PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
+PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, and
+PCRE_PARTIAL_SOFT.
+</P>
+<P>
+If the pattern was successfully studied with one of the just-in-time (JIT)
+compile options, the only supported options for JIT execution are
+PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,
+PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. If an
+unsupported option is used, JIT execution is disabled and the normal
+interpretive code in <b>pcre_exec()</b> is run.
+<pre>
+ PCRE_ANCHORED
+</pre>
+The PCRE_ANCHORED option limits <b>pcre_exec()</b> to matching at the first
+matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
+to be anchored by virtue of its contents, it cannot be made unachored at
+matching time.
+<pre>
+ PCRE_BSR_ANYCRLF
+ PCRE_BSR_UNICODE
+</pre>
+These options (which are mutually exclusive) control what the \R escape
+sequence matches. The choice is either to match only CR, LF, or CRLF, or to
+match any Unicode newline sequence. These options override the choice that was
+made or defaulted when the pattern was compiled.
+<pre>
+ PCRE_NEWLINE_CR
+ PCRE_NEWLINE_LF
+ PCRE_NEWLINE_CRLF
+ PCRE_NEWLINE_ANYCRLF
+ PCRE_NEWLINE_ANY
+</pre>
+These options override the newline definition that was chosen or defaulted when
+the pattern was compiled. For details, see the description of
+<b>pcre_compile()</b> above. During matching, the newline choice affects the
+behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
+the way the match position is advanced after a match failure for an unanchored
+pattern.
+</P>
+<P>
+When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is set, and a
+match attempt for an unanchored pattern fails when the current position is at a
+CRLF sequence, and the pattern contains no explicit matches for CR or LF
+characters, the match position is advanced by two characters instead of one, in
+other words, to after the CRLF.
+</P>
+<P>
+The above rule is a compromise that makes the most common cases work as
+expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not
+set), it does not match the string "\r\nA" because, after failing at the
+start, it skips both the CR and the LF before retrying. However, the pattern
+[\r\n]A does match that string, because it contains an explicit CR or LF
+reference, and so advances only by one character after the first failure.
+</P>
+<P>
+An explicit match for CR of LF is either a literal appearance of one of those
+characters, or one of the \r or \n escape sequences. Implicit matches such as
+[^X] do not count, nor does \s (which includes CR and LF in the characters
+that it matches).
+</P>
+<P>
+Notwithstanding the above, anomalous effects may still occur when CRLF is a
+valid newline sequence and explicit \r or \n escapes appear in the pattern.
+<pre>
+ PCRE_NOTBOL
+</pre>
+This option specifies that first character of the subject string is not the
+beginning of a line, so the circumflex metacharacter should not match before
+it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
+never to match. This option affects only the behaviour of the circumflex
+metacharacter. It does not affect \A.
+<pre>
+ PCRE_NOTEOL
+</pre>
+This option specifies that the end of the subject string is not the end of a
+line, so the dollar metacharacter should not match it nor (except in multiline
+mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
+compile time) causes dollar never to match. This option affects only the
+behaviour of the dollar metacharacter. It does not affect \Z or \z.
+<pre>
+ PCRE_NOTEMPTY
+</pre>
+An empty string is not considered to be a valid match if this option is set. If
+there are alternatives in the pattern, they are tried. If all the alternatives
+match the empty string, the entire match fails. For example, if the pattern
+<pre>
+ a?b?
+</pre>
+is applied to a string not beginning with "a" or "b", it matches an empty
+string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
+valid, so PCRE searches further into the string for occurrences of "a" or "b".
+<pre>
+ PCRE_NOTEMPTY_ATSTART
+</pre>
+This is like PCRE_NOTEMPTY, except that an empty string match that is not at
+the start of the subject is permitted. If the pattern is anchored, such a match
+can occur only if the pattern contains \K.
+</P>
+<P>
+Perl has no direct equivalent of PCRE_NOTEMPTY or PCRE_NOTEMPTY_ATSTART, but it
+does make a special case of a pattern match of the empty string within its
+<b>split()</b> function, and when using the /g modifier. It is possible to
+emulate Perl's behaviour after matching a null string by first trying the match
+again at the same offset with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then
+if that fails, by advancing the starting offset (see below) and trying an
+ordinary match again. There is some code that demonstrates how to do this in
+the
+<a href="pcredemo.html"><b>pcredemo</b></a>
+sample program. In the most general case, you have to check to see if the
+newline convention recognizes CRLF as a newline, and if so, and the current
+character is CR followed by LF, advance the starting offset by two characters
+instead of one.
+<pre>
+ PCRE_NO_START_OPTIMIZE
+</pre>
+There are a number of optimizations that <b>pcre_exec()</b> uses at the start of
+a match, in order to speed up the process. For example, if it is known that an
+unanchored match must start with a specific character, it searches the subject
+for that character, and fails immediately if it cannot find it, without
+actually running the main matching function. This means that a special item
+such as (*COMMIT) at the start of a pattern is not considered until after a
+suitable starting point for the match has been found. Also, when callouts or
+(*MARK) items are in use, these "start-up" optimizations can cause them to be
+skipped if the pattern is never actually used. The start-up optimizations are
+in effect a pre-scan of the subject that takes place before the pattern is run.
+</P>
+<P>
+The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations, possibly
+causing performance to suffer, but ensuring that in cases where the result is
+"no match", the callouts do occur, and that items such as (*COMMIT) and (*MARK)
+are considered at every possible starting position in the subject string. If
+PCRE_NO_START_OPTIMIZE is set at compile time, it cannot be unset at matching
+time. The use of PCRE_NO_START_OPTIMIZE at matching time (that is, passing it
+to <b>pcre_exec()</b>) disables JIT execution; in this situation, matching is
+always done using interpretively.
+</P>
+<P>
+Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching operation.
+Consider the pattern
+<pre>
+ (*COMMIT)ABC
+</pre>
+When this is compiled, PCRE records the fact that a match must start with the
+character "A". Suppose the subject string is "DEFABC". The start-up
+optimization scans along the subject, finds "A" and runs the first match
+attempt from there. The (*COMMIT) item means that the pattern must match the
+current starting position, which in this case, it does. However, if the same
+match is run with PCRE_NO_START_OPTIMIZE set, the initial scan along the
+subject string does not happen. The first match attempt is run starting from
+"D" and when this fails, (*COMMIT) prevents any further matches being tried, so
+the overall result is "no match". If the pattern is studied, more start-up
+optimizations may be used. For example, a minimum length for the subject may be
+recorded. Consider the pattern
+<pre>
+ (*MARK:A)(X|Y)
+</pre>
+The minimum length for a match is one character. If the subject is "ABC", there
+will be attempts to match "ABC", "BC", "C", and then finally an empty string.
+If the pattern is studied, the final attempt does not take place, because PCRE
+knows that the subject is too short, and so the (*MARK) is never encountered.
+In this case, studying the pattern does not affect the overall match result,
+which is still "no match", but it does affect the auxiliary information that is
+returned.
+<pre>
+ PCRE_NO_UTF8_CHECK
+</pre>
+When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
+string is automatically checked when <b>pcre_exec()</b> is subsequently called.
+The entire string is checked before any other processing takes place. The value
+of <i>startoffset</i> is also checked to ensure that it points to the start of a
+UTF-8 character. There is a discussion about the
+<a href="pcreunicode.html#utf8strings">validity of UTF-8 strings</a>
+in the
+<a href="pcreunicode.html"><b>pcreunicode</b></a>
+page. If an invalid sequence of bytes is found, <b>pcre_exec()</b> returns the
+error PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is a
+truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8. In both
+cases, information about the precise nature of the error may also be returned
+(see the descriptions of these errors in the section entitled \fIError return
+values from\fP <b>pcre_exec()</b>
+<a href="#errorlist">below).</a>
+If <i>startoffset</i> contains a value that does not point to the start of a
+UTF-8 character (or to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is
+returned.
+</P>
+<P>
+If you already know that your subject is valid, and you want to skip these
+checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
+calling <b>pcre_exec()</b>. You might want to do this for the second and
+subsequent calls to <b>pcre_exec()</b> if you are making repeated calls to find
+all the matches in a single subject string. However, you should be sure that
+the value of <i>startoffset</i> points to the start of a character (or the end
+of the subject). When PCRE_NO_UTF8_CHECK is set, the effect of passing an
+invalid string as a subject or an invalid value of <i>startoffset</i> is
+undefined. Your program may crash or loop.
+<pre>
+ PCRE_PARTIAL_HARD
+ PCRE_PARTIAL_SOFT
+</pre>
+These options turn on the partial matching feature. For backwards
+compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial match
+occurs if the end of the subject string is reached successfully, but there are
+not enough subject characters to complete the match. If this happens when
+PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set, matching continues by
+testing any remaining alternatives. Only if no complete match can be found is
+PCRE_ERROR_PARTIAL returned instead of PCRE_ERROR_NOMATCH. In other words,
+PCRE_PARTIAL_SOFT says that the caller is prepared to handle a partial match,
+but only if no complete match can be found.
+</P>
+<P>
+If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this case, if a
+partial match is found, <b>pcre_exec()</b> immediately returns
+PCRE_ERROR_PARTIAL, without considering any other alternatives. In other words,
+when PCRE_PARTIAL_HARD is set, a partial match is considered to be more
+important that an alternative complete match.
+</P>
+<P>
+In both cases, the portion of the string that was inspected when the partial
+match was found is set as the first matching string. There is a more detailed
+discussion of partial and multi-segment matching, with examples, in the
+<a href="pcrepartial.html"><b>pcrepartial</b></a>
+documentation.
+</P>
+<br><b>
+The string to be matched by <b>pcre_exec()</b>
+</b><br>
+<P>
+The subject string is passed to <b>pcre_exec()</b> as a pointer in
+<i>subject</i>, a length in <i>length</i>, and a starting offset in
+<i>startoffset</i>. The units for <i>length</i> and <i>startoffset</i> are bytes
+for the 8-bit library, 16-bit data items for the 16-bit library, and 32-bit
+data items for the 32-bit library.
+</P>
+<P>
+If <i>startoffset</i> is negative or greater than the length of the subject,
+<b>pcre_exec()</b> returns PCRE_ERROR_BADOFFSET. When the starting offset is
+zero, the search for a match starts at the beginning of the subject, and this
+is by far the most common case. In UTF-8 or UTF-16 mode, the offset must point
+to the start of a character, or the end of the subject (in UTF-32 mode, one
+data unit equals one character, so all offsets are valid). Unlike the pattern
+string, the subject may contain binary zeroes.
+</P>
+<P>
+A non-zero starting offset is useful when searching for another match in the
+same subject by calling <b>pcre_exec()</b> again after a previous success.
+Setting <i>startoffset</i> differs from just passing over a shortened string and
+setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
+lookbehind. For example, consider the pattern
+<pre>
+ \Biss\B
+</pre>
+which finds occurrences of "iss" in the middle of words. (\B matches only if
+the current position in the subject is not a word boundary.) When applied to
+the string "Mississipi" the first call to <b>pcre_exec()</b> finds the first
+occurrence. If <b>pcre_exec()</b> is called again with just the remainder of the
+subject, namely "issipi", it does not match, because \B is always false at the
+start of the subject, which is deemed to be a word boundary. However, if
+<b>pcre_exec()</b> is passed the entire string again, but with <i>startoffset</i>
+set to 4, it finds the second occurrence of "iss" because it is able to look
+behind the starting point to discover that it is preceded by a letter.
+</P>
+<P>
+Finding all the matches in a subject is tricky when the pattern can match an
+empty string. It is possible to emulate Perl's /g behaviour by first trying the
+match again at the same offset, with the PCRE_NOTEMPTY_ATSTART and
+PCRE_ANCHORED options, and then if that fails, advancing the starting offset
+and trying an ordinary match again. There is some code that demonstrates how to
+do this in the
+<a href="pcredemo.html"><b>pcredemo</b></a>
+sample program. In the most general case, you have to check to see if the
+newline convention recognizes CRLF as a newline, and if so, and the current
+character is CR followed by LF, advance the starting offset by two characters
+instead of one.
+</P>
+<P>
+If a non-zero starting offset is passed when the pattern is anchored, one
+attempt to match at the given offset is made. This can only succeed if the
+pattern does not require the match to be at the start of the subject.
+</P>
+<br><b>
+How <b>pcre_exec()</b> returns captured substrings
+</b><br>
+<P>
+In general, a pattern matches a certain portion of the subject, and in
+addition, further substrings from the subject may be picked out by parts of the
+pattern. Following the usage in Jeffrey Friedl's book, this is called
+"capturing" in what follows, and the phrase "capturing subpattern" is used for
+a fragment of a pattern that picks out a substring. PCRE supports several other
+kinds of parenthesized subpattern that do not cause substrings to be captured.
+</P>
+<P>
+Captured substrings are returned to the caller via a vector of integers whose
+address is passed in <i>ovector</i>. The number of elements in the vector is
+passed in <i>ovecsize</i>, which must be a non-negative number. <b>Note</b>: this
+argument is NOT the size of <i>ovector</i> in bytes.
+</P>
+<P>
+The first two-thirds of the vector is used to pass back captured substrings,
+each substring using a pair of integers. The remaining third of the vector is
+used as workspace by <b>pcre_exec()</b> while matching capturing subpatterns,
+and is not available for passing back information. The number passed in
+<i>ovecsize</i> should always be a multiple of three. If it is not, it is
+rounded down.
+</P>
+<P>
+When a match is successful, information about captured substrings is returned
+in pairs of integers, starting at the beginning of <i>ovector</i>, and
+continuing up to two-thirds of its length at the most. The first element of
+each pair is set to the offset of the first character in a substring, and the
+second is set to the offset of the first character after the end of a
+substring. These values are always data unit offsets, even in UTF mode. They
+are byte offsets in the 8-bit library, 16-bit data item offsets in the 16-bit
+library, and 32-bit data item offsets in the 32-bit library. <b>Note</b>: they
+are not character counts.
+</P>
+<P>
+The first pair of integers, <i>ovector[0]</i> and <i>ovector[1]</i>, identify the
+portion of the subject string matched by the entire pattern. The next pair is
+used for the first capturing subpattern, and so on. The value returned by
+<b>pcre_exec()</b> is one more than the highest numbered pair that has been set.
+For example, if two substrings have been captured, the returned value is 3. If
+there are no capturing subpatterns, the return value from a successful match is
+1, indicating that just the first pair of offsets has been set.
+</P>
+<P>
+If a capturing subpattern is matched repeatedly, it is the last portion of the
+string that it matched that is returned.
+</P>
+<P>
+If the vector is too small to hold all the captured substring offsets, it is
+used as far as possible (up to two-thirds of its length), and the function
+returns a value of zero. If neither the actual string matched nor any captured
+substrings are of interest, <b>pcre_exec()</b> may be called with <i>ovector</i>
+passed as NULL and <i>ovecsize</i> as zero. However, if the pattern contains
+back references and the <i>ovector</i> is not big enough to remember the related
+substrings, PCRE has to get additional memory for use during matching. Thus it
+is usually advisable to supply an <i>ovector</i> of reasonable size.
+</P>
+<P>
+There are some cases where zero is returned (indicating vector overflow) when
+in fact the vector is exactly the right size for the final match. For example,
+consider the pattern
+<pre>
+ (a)(?:(b)c|bd)
+</pre>
+If a vector of 6 elements (allowing for only 1 captured substring) is given
+with subject string "abd", <b>pcre_exec()</b> will try to set the second
+captured string, thereby recording a vector overflow, before failing to match
+"c" and backing up to try the second alternative. The zero return, however,
+does correctly indicate that the maximum number of slots (namely 2) have been
+filled. In similar cases where there is temporary overflow, but the final
+number of used slots is actually less than the maximum, a non-zero value is
+returned.
+</P>
+<P>
+The <b>pcre_fullinfo()</b> function can be used to find out how many capturing
+subpatterns there are in a compiled pattern. The smallest size for
+<i>ovector</i> that will allow for <i>n</i> captured substrings, in addition to
+the offsets of the substring matched by the whole pattern, is (<i>n</i>+1)*3.
+</P>
+<P>
+It is possible for capturing subpattern number <i>n+1</i> to match some part of
+the subject when subpattern <i>n</i> has not been used at all. For example, if
+the string "abc" is matched against the pattern (a|(z))(bc) the return from the
+function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
+happens, both values in the offset pairs corresponding to unused subpatterns
+are set to -1.
+</P>
+<P>
+Offset values that correspond to unused subpatterns at the end of the
+expression are also set to -1. For example, if the string "abc" is matched
+against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
+return from the function is 2, because the highest used capturing subpattern
+number is 1, and the offsets for for the second and third capturing subpatterns
+(assuming the vector is large enough, of course) are set to -1.
+</P>
+<P>
+<b>Note</b>: Elements in the first two-thirds of <i>ovector</i> that do not
+correspond to capturing parentheses in the pattern are never changed. That is,
+if a pattern contains <i>n</i> capturing parentheses, no more than
+<i>ovector[0]</i> to <i>ovector[2n+1]</i> are set by <b>pcre_exec()</b>. The other
+elements (in the first two-thirds) retain whatever values they previously had.
+</P>
+<P>
+Some convenience functions are provided for extracting the captured substrings
+as separate strings. These are described below.
+<a name="errorlist"></a></P>
+<br><b>
+Error return values from <b>pcre_exec()</b>
+</b><br>
+<P>
+If <b>pcre_exec()</b> fails, it returns a negative number. The following are
+defined in the header file:
+<pre>
+ PCRE_ERROR_NOMATCH (-1)
+</pre>
+The subject string did not match the pattern.
+<pre>
+ PCRE_ERROR_NULL (-2)
+</pre>
+Either <i>code</i> or <i>subject</i> was passed as NULL, or <i>ovector</i> was
+NULL and <i>ovecsize</i> was not zero.
+<pre>
+ PCRE_ERROR_BADOPTION (-3)
+</pre>
+An unrecognized bit was set in the <i>options</i> argument.
+<pre>
+ PCRE_ERROR_BADMAGIC (-4)
+</pre>
+PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
+the case when it is passed a junk pointer and to detect when a pattern that was
+compiled in an environment of one endianness is run in an environment with the
+other endianness. This is the error that PCRE gives when the magic number is
+not present.
+<pre>
+ PCRE_ERROR_UNKNOWN_OPCODE (-5)
+</pre>
+While running the pattern match, an unknown item was encountered in the
+compiled pattern. This error could be caused by a bug in PCRE or by overwriting
+of the compiled pattern.
+<pre>
+ PCRE_ERROR_NOMEMORY (-6)
+</pre>
+If a pattern contains back references, but the <i>ovector</i> that is passed to
+<b>pcre_exec()</b> is not big enough to remember the referenced substrings, PCRE
+gets a block of memory at the start of matching to use for this purpose. If the
+call via <b>pcre_malloc()</b> fails, this error is given. The memory is
+automatically freed at the end of matching.
+</P>
+<P>
+This error is also given if <b>pcre_stack_malloc()</b> fails in
+<b>pcre_exec()</b>. This can happen only when PCRE has been compiled with
+<b>--disable-stack-for-recursion</b>.
+<pre>
+ PCRE_ERROR_NOSUBSTRING (-7)
+</pre>
+This error is used by the <b>pcre_copy_substring()</b>,
+<b>pcre_get_substring()</b>, and <b>pcre_get_substring_list()</b> functions (see
+below). It is never returned by <b>pcre_exec()</b>.
+<pre>
+ PCRE_ERROR_MATCHLIMIT (-8)
+</pre>
+The backtracking limit, as specified by the <i>match_limit</i> field in a
+<b>pcre_extra</b> structure (or defaulted) was reached. See the description
+above.
+<pre>
+ PCRE_ERROR_CALLOUT (-9)
+</pre>
+This error is never generated by <b>pcre_exec()</b> itself. It is provided for
+use by callout functions that want to yield a distinctive error code. See the
+<a href="pcrecallout.html"><b>pcrecallout</b></a>
+documentation for details.
+<pre>
+ PCRE_ERROR_BADUTF8 (-10)
+</pre>
+A string that contains an invalid UTF-8 byte sequence was passed as a subject,
+and the PCRE_NO_UTF8_CHECK option was not set. If the size of the output vector
+(<i>ovecsize</i>) is at least 2, the byte offset to the start of the the invalid
+UTF-8 character is placed in the first element, and a reason code is placed in
+the second element. The reason codes are listed in the
+<a href="#badutf8reasons">following section.</a>
+For backward compatibility, if PCRE_PARTIAL_HARD is set and the problem is a
+truncated UTF-8 character at the end of the subject (reason codes 1 to 5),
+PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.
+<pre>
+ PCRE_ERROR_BADUTF8_OFFSET (-11)
+</pre>
+The UTF-8 byte sequence that was passed as a subject was checked and found to
+be valid (the PCRE_NO_UTF8_CHECK option was not set), but the value of
+<i>startoffset</i> did not point to the beginning of a UTF-8 character or the
+end of the subject.
+<pre>
+ PCRE_ERROR_PARTIAL (-12)
+</pre>
+The subject string did not match, but it did match partially. See the
+<a href="pcrepartial.html"><b>pcrepartial</b></a>
+documentation for details of partial matching.
+<pre>
+ PCRE_ERROR_BADPARTIAL (-13)
+</pre>
+This code is no longer in use. It was formerly returned when the PCRE_PARTIAL
+option was used with a compiled pattern containing items that were not
+supported for partial matching. From release 8.00 onwards, there are no
+restrictions on partial matching.
+<pre>
+ PCRE_ERROR_INTERNAL (-14)
+</pre>
+An unexpected internal error has occurred. This error could be caused by a bug
+in PCRE or by overwriting of the compiled pattern.
+<pre>
+ PCRE_ERROR_BADCOUNT (-15)
+</pre>
+This error is given if the value of the <i>ovecsize</i> argument is negative.
+<pre>
+ PCRE_ERROR_RECURSIONLIMIT (-21)
+</pre>
+The internal recursion limit, as specified by the <i>match_limit_recursion</i>
+field in a <b>pcre_extra</b> structure (or defaulted) was reached. See the
+description above.
+<pre>
+ PCRE_ERROR_BADNEWLINE (-23)
+</pre>
+An invalid combination of PCRE_NEWLINE_<i>xxx</i> options was given.
+<pre>
+ PCRE_ERROR_BADOFFSET (-24)
+</pre>
+The value of <i>startoffset</i> was negative or greater than the length of the
+subject, that is, the value in <i>length</i>.
+<pre>
+ PCRE_ERROR_SHORTUTF8 (-25)
+</pre>
+This error is returned instead of PCRE_ERROR_BADUTF8 when the subject string
+ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD option is set.
+Information about the failure is returned as for PCRE_ERROR_BADUTF8. It is in
+fact sufficient to detect this case, but this special error code for
+PCRE_PARTIAL_HARD precedes the implementation of returned information; it is
+retained for backwards compatibility.
+<pre>
+ PCRE_ERROR_RECURSELOOP (-26)
+</pre>
+This error is returned when <b>pcre_exec()</b> detects a recursion loop within
+the pattern. Specifically, it means that either the whole pattern or a
+subpattern has been called recursively for the second time at the same position
+in the subject string. Some simple patterns that might do this are detected and
+faulted at compile time, but more complicated cases, in particular mutual
+recursions between two different subpatterns, cannot be detected until run
+time.
+<pre>
+ PCRE_ERROR_JIT_STACKLIMIT (-27)
+</pre>
+This error is returned when a pattern that was successfully studied using a
+JIT compile option is being matched, but the memory available for the
+just-in-time processing stack is not large enough. See the
+<a href="pcrejit.html"><b>pcrejit</b></a>
+documentation for more details.
+<pre>
+ PCRE_ERROR_BADMODE (-28)
+</pre>
+This error is given if a pattern that was compiled by the 8-bit library is
+passed to a 16-bit or 32-bit library function, or vice versa.
+<pre>
+ PCRE_ERROR_BADENDIANNESS (-29)
+</pre>
+This error is given if a pattern that was compiled and saved is reloaded on a
+host with different endianness. The utility function
+<b>pcre_pattern_to_host_byte_order()</b> can be used to convert such a pattern
+so that it runs on the new host.
+<pre>
+ PCRE_ERROR_JIT_BADOPTION
+</pre>
+This error is returned when a pattern that was successfully studied using a JIT
+compile option is being matched, but the matching mode (partial or complete
+match) does not correspond to any JIT compilation mode. When the JIT fast path
+function is used, this error may be also given for invalid options. See the
+<a href="pcrejit.html"><b>pcrejit</b></a>
+documentation for more details.
+<pre>
+ PCRE_ERROR_BADLENGTH (-32)
+</pre>
+This error is given if <b>pcre_exec()</b> is called with a negative value for
+the <i>length</i> argument.
+</P>
+<P>
+Error numbers -16 to -20, -22, and 30 are not used by <b>pcre_exec()</b>.
+<a name="badutf8reasons"></a></P>
+<br><b>
+Reason codes for invalid UTF-8 strings
+</b><br>
+<P>
+This section applies only to the 8-bit library. The corresponding information
+for the 16-bit and 32-bit libraries is given in the
+<a href="pcre16.html"><b>pcre16</b></a>
+and
+<a href="pcre32.html"><b>pcre32</b></a>
+pages.
+</P>
+<P>
+When <b>pcre_exec()</b> returns either PCRE_ERROR_BADUTF8 or
+PCRE_ERROR_SHORTUTF8, and the size of the output vector (<i>ovecsize</i>) is at
+least 2, the offset of the start of the invalid UTF-8 character is placed in
+the first output vector element (<i>ovector[0]</i>) and a reason code is placed
+in the second element (<i>ovector[1]</i>). The reason codes are given names in
+the <b>pcre.h</b> header file:
+<pre>
+ PCRE_UTF8_ERR1
+ PCRE_UTF8_ERR2
+ PCRE_UTF8_ERR3
+ PCRE_UTF8_ERR4
+ PCRE_UTF8_ERR5
+</pre>
+The string ends with a truncated UTF-8 character; the code specifies how many
+bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 characters to be
+no longer than 4 bytes, the encoding scheme (originally defined by RFC 2279)
+allows for up to 6 bytes, and this is checked first; hence the possibility of
+4 or 5 missing bytes.
+<pre>
+ PCRE_UTF8_ERR6
+ PCRE_UTF8_ERR7
+ PCRE_UTF8_ERR8
+ PCRE_UTF8_ERR9
+ PCRE_UTF8_ERR10
+</pre>
+The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of the
+character do not have the binary value 0b10 (that is, either the most
+significant bit is 0, or the next bit is 1).
+<pre>
+ PCRE_UTF8_ERR11
+ PCRE_UTF8_ERR12
+</pre>
+A character that is valid by the RFC 2279 rules is either 5 or 6 bytes long;
+these code points are excluded by RFC 3629.
+<pre>
+ PCRE_UTF8_ERR13
+</pre>
+A 4-byte character has a value greater than 0x10fff; these code points are
+excluded by RFC 3629.
+<pre>
+ PCRE_UTF8_ERR14
+</pre>
+A 3-byte character has a value in the range 0xd800 to 0xdfff; this range of
+code points are reserved by RFC 3629 for use with UTF-16, and so are excluded
+from UTF-8.
+<pre>
+ PCRE_UTF8_ERR15
+ PCRE_UTF8_ERR16
+ PCRE_UTF8_ERR17
+ PCRE_UTF8_ERR18
+ PCRE_UTF8_ERR19
+</pre>
+A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes for a
+value that can be represented by fewer bytes, which is invalid. For example,
+the two bytes 0xc0, 0xae give the value 0x2e, whose correct coding uses just
+one byte.
+<pre>
+ PCRE_UTF8_ERR20
+</pre>
+The two most significant bits of the first byte of a character have the binary
+value 0b10 (that is, the most significant bit is 1 and the second is 0). Such a
+byte can only validly occur as the second or subsequent byte of a multi-byte
+character.
+<pre>
+ PCRE_UTF8_ERR21
+</pre>
+The first byte of a character has the value 0xfe or 0xff. These values can
+never occur in a valid UTF-8 string.
+<pre>
+ PCRE_UTF8_ERR22
+</pre>
+This error code was formerly used when the presence of a so-called
+"non-character" caused an error. Unicode corrigendum #9 makes it clear that
+such characters should not cause a string to be rejected, and so this code is
+no longer in use and is never returned.
+</P>
+<br><a name="SEC18" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NUMBER</a><br>
+<P>
+<b>int pcre_copy_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
+<b> int <i>stringcount</i>, int <i>stringnumber</i>, char *<i>buffer</i>,</b>
+<b> int <i>buffersize</i>);</b>
+<br>
+<br>
+<b>int pcre_get_substring(const char *<i>subject</i>, int *<i>ovector</i>,</b>
+<b> int <i>stringcount</i>, int <i>stringnumber</i>,</b>
+<b> const char **<i>stringptr</i>);</b>
+<br>
+<br>
+<b>int pcre_get_substring_list(const char *<i>subject</i>,</b>
+<b> int *<i>ovector</i>, int <i>stringcount</i>, const char ***<i>listptr</i>);</b>
+</P>
+<P>
+Captured substrings can be accessed directly by using the offsets returned by
+<b>pcre_exec()</b> in <i>ovector</i>. For convenience, the functions
+<b>pcre_copy_substring()</b>, <b>pcre_get_substring()</b>, and
+<b>pcre_get_substring_list()</b> are provided for extracting captured substrings
+as new, separate, zero-terminated strings. These functions identify substrings
+by number. The next section describes functions for extracting named
+substrings.
+</P>
+<P>
+A substring that contains a binary zero is correctly extracted and has a
+further zero added on the end, but the result is not, of course, a C string.
+However, you can process such a string by referring to the length that is
+returned by <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>.
+Unfortunately, the interface to <b>pcre_get_substring_list()</b> is not adequate
+for handling strings containing binary zeros, because the end of the final
+string is not independently indicated.
+</P>
+<P>
+The first three arguments are the same for all three of these functions:
+<i>subject</i> is the subject string that has just been successfully matched,
+<i>ovector</i> is a pointer to the vector of integer offsets that was passed to
+<b>pcre_exec()</b>, and <i>stringcount</i> is the number of substrings that were
+captured by the match, including the substring that matched the entire regular
+expression. This is the value returned by <b>pcre_exec()</b> if it is greater
+than zero. If <b>pcre_exec()</b> returned zero, indicating that it ran out of
+space in <i>ovector</i>, the value passed as <i>stringcount</i> should be the
+number of elements in the vector divided by three.
+</P>
+<P>
+The functions <b>pcre_copy_substring()</b> and <b>pcre_get_substring()</b>
+extract a single substring, whose number is given as <i>stringnumber</i>. A
+value of zero extracts the substring that matched the entire pattern, whereas
+higher values extract the captured substrings. For <b>pcre_copy_substring()</b>,
+the string is placed in <i>buffer</i>, whose length is given by
+<i>buffersize</i>, while for <b>pcre_get_substring()</b> a new block of memory is
+obtained via <b>pcre_malloc</b>, and its address is returned via
+<i>stringptr</i>. The yield of the function is the length of the string, not
+including the terminating zero, or one of these error codes:
+<pre>
+ PCRE_ERROR_NOMEMORY (-6)
+</pre>
+The buffer was too small for <b>pcre_copy_substring()</b>, or the attempt to get
+memory failed for <b>pcre_get_substring()</b>.
+<pre>
+ PCRE_ERROR_NOSUBSTRING (-7)
+</pre>
+There is no substring whose number is <i>stringnumber</i>.
+</P>
+<P>
+The <b>pcre_get_substring_list()</b> function extracts all available substrings
+and builds a list of pointers to them. All this is done in a single block of
+memory that is obtained via <b>pcre_malloc</b>. The address of the memory block
+is returned via <i>listptr</i>, which is also the start of the list of string
+pointers. The end of the list is marked by a NULL pointer. The yield of the
+function is zero if all went well, or the error code
+<pre>
+ PCRE_ERROR_NOMEMORY (-6)
+</pre>
+if the attempt to get the memory block failed.
+</P>
+<P>
+When any of these functions encounter a substring that is unset, which can
+happen when capturing subpattern number <i>n+1</i> matches some part of the
+subject, but subpattern <i>n</i> has not been used at all, they return an empty
+string. This can be distinguished from a genuine zero-length substring by
+inspecting the appropriate offset in <i>ovector</i>, which is negative for unset
+substrings.
+</P>
+<P>
+The two convenience functions <b>pcre_free_substring()</b> and
+<b>pcre_free_substring_list()</b> can be used to free the memory returned by
+a previous call of <b>pcre_get_substring()</b> or
+<b>pcre_get_substring_list()</b>, respectively. They do nothing more than call
+the function pointed to by <b>pcre_free</b>, which of course could be called
+directly from a C program. However, PCRE is used in some situations where it is
+linked via a special interface to another programming language that cannot use
+<b>pcre_free</b> directly; it is for these cases that the functions are
+provided.
+</P>
+<br><a name="SEC19" href="#TOC1">EXTRACTING CAPTURED SUBSTRINGS BY NAME</a><br>
+<P>
+<b>int pcre_get_stringnumber(const pcre *<i>code</i>,</b>
+<b> const char *<i>name</i>);</b>
+<br>
+<br>
+<b>int pcre_copy_named_substring(const pcre *<i>code</i>,</b>
+<b> const char *<i>subject</i>, int *<i>ovector</i>,</b>
+<b> int <i>stringcount</i>, const char *<i>stringname</i>,</b>
+<b> char *<i>buffer</i>, int <i>buffersize</i>);</b>
+<br>
+<br>
+<b>int pcre_get_named_substring(const pcre *<i>code</i>,</b>
+<b> const char *<i>subject</i>, int *<i>ovector</i>,</b>
+<b> int <i>stringcount</i>, const char *<i>stringname</i>,</b>
+<b> const char **<i>stringptr</i>);</b>
+</P>
+<P>
+To extract a substring by name, you first have to find associated number.
+For example, for this pattern
+<pre>
+ (a+)b(?&#60;xxx&#62;\d+)...
+</pre>
+the number of the subpattern called "xxx" is 2. If the name is known to be
+unique (PCRE_DUPNAMES was not set), you can find the number from the name by
+calling <b>pcre_get_stringnumber()</b>. The first argument is the compiled
+pattern, and the second is the name. The yield of the function is the
+subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
+that name.
+</P>
+<P>
+Given the number, you can extract the substring directly, or use one of the
+functions described in the previous section. For convenience, there are also
+two functions that do the whole job.
+</P>
+<P>
+Most of the arguments of <b>pcre_copy_named_substring()</b> and
+<b>pcre_get_named_substring()</b> are the same as those for the similarly named
+functions that extract by number. As these are described in the previous
+section, they are not re-described here. There are just two differences:
+</P>
+<P>
+First, instead of a substring number, a substring name is given. Second, there
+is an extra argument, given at the start, which is a pointer to the compiled
+pattern. This is needed in order to gain access to the name-to-number
+translation table.
+</P>
+<P>
+These functions call <b>pcre_get_stringnumber()</b>, and if it succeeds, they
+then call <b>pcre_copy_substring()</b> or <b>pcre_get_substring()</b>, as
+appropriate. <b>NOTE:</b> If PCRE_DUPNAMES is set and there are duplicate names,
+the behaviour may not be what you want (see the next section).
+</P>
+<P>
+<b>Warning:</b> If the pattern uses the (?| feature to set up multiple
+subpatterns with the same number, as described in the
+<a href="pcrepattern.html#dupsubpatternnumber">section on duplicate subpattern numbers</a>
+in the
+<a href="pcrepattern.html"><b>pcrepattern</b></a>
+page, you cannot use names to distinguish the different subpatterns, because
+names are not included in the compiled code. The matching process uses only
+numbers. For this reason, the use of different names for subpatterns of the
+same number causes an error at compile time.
+</P>
+<br><a name="SEC20" href="#TOC1">DUPLICATE SUBPATTERN NAMES</a><br>
+<P>
+<b>int pcre_get_stringtable_entries(const pcre *<i>code</i>,</b>
+<b> const char *<i>name</i>, char **<i>first</i>, char **<i>last</i>);</b>
+</P>
+<P>
+When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
+are not required to be unique. (Duplicate names are always allowed for
+subpatterns with the same number, created by using the (?| feature. Indeed, if
+such subpatterns are named, they are required to use the same names.)
+</P>
+<P>
+Normally, patterns with duplicate names are such that in any one match, only
+one of the named subpatterns participates. An example is shown in the
+<a href="pcrepattern.html"><b>pcrepattern</b></a>
+documentation.
+</P>
+<P>
+When duplicates are present, <b>pcre_copy_named_substring()</b> and
+<b>pcre_get_named_substring()</b> return the first substring corresponding to
+the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is
+returned; no data is returned. The <b>pcre_get_stringnumber()</b> function
+returns one of the numbers that are associated with the name, but it is not
+defined which it is.
+</P>
+<P>
+If you want to get full details of all captured substrings for a given name,
+you must use the <b>pcre_get_stringtable_entries()</b> function. The first
+argument is the compiled pattern, and the second is the name. The third and
+fourth are pointers to variables which are updated by the function. After it
+has run, they point to the first and last entries in the name-to-number table
+for the given name. The function itself returns the length of each entry, or
+PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
+described above in the section entitled <i>Information about a pattern</i>
+<a href="#infoaboutpattern">above.</a>
+Given all the relevant entries for the name, you can extract each of their
+numbers, and hence the captured data, if any.
+</P>
+<br><a name="SEC21" href="#TOC1">FINDING ALL POSSIBLE MATCHES</a><br>
+<P>
+The traditional matching function uses a similar algorithm to Perl, which stops
+when it finds the first match, starting at a given point in the subject. If you
+want to find all possible matches, or the longest possible match, consider
+using the alternative matching function (see below) instead. If you cannot use
+the alternative function, but still need to find all possible matches, you
+can kludge it up by making use of the callout facility, which is described in
+the
+<a href="pcrecallout.html"><b>pcrecallout</b></a>
+documentation.
+</P>
+<P>
+What you have to do is to insert a callout right at the end of the pattern.
+When your callout function is called, extract and save the current matched
+substring. Then return 1, which forces <b>pcre_exec()</b> to backtrack and try
+other alternatives. Ultimately, when it runs out of matches, <b>pcre_exec()</b>
+will yield PCRE_ERROR_NOMATCH.
+</P>
+<br><a name="SEC22" href="#TOC1">OBTAINING AN ESTIMATE OF STACK USAGE</a><br>
+<P>
+Matching certain patterns using <b>pcre_exec()</b> can use a lot of process
+stack, which in certain environments can be rather limited in size. Some users
+find it helpful to have an estimate of the amount of stack that is used by
+<b>pcre_exec()</b>, to help them set recursion limits, as described in the
+<a href="pcrestack.html"><b>pcrestack</b></a>
+documentation. The estimate that is output by <b>pcretest</b> when called with
+the <b>-m</b> and <b>-C</b> options is obtained by calling <b>pcre_exec</b> with
+the values NULL, NULL, NULL, -999, and -999 for its first five arguments.
+</P>
+<P>
+Normally, if its first argument is NULL, <b>pcre_exec()</b> immediately returns
+the negative error code PCRE_ERROR_NULL, but with this special combination of
+arguments, it returns instead a negative number whose absolute value is the
+approximate stack frame size in bytes. (A negative number is used so that it is
+clear that no match has happened.) The value is approximate because in some
+cases, recursive calls to <b>pcre_exec()</b> occur when there are one or two
+additional variables on the stack.
+</P>
+<P>
+If PCRE has been compiled to use the heap instead of the stack for recursion,
+the value returned is the size of each block that is obtained from the heap.
+<a name="dfamatch"></a></P>
+<br><a name="SEC23" href="#TOC1">MATCHING A PATTERN: THE ALTERNATIVE FUNCTION</a><br>
+<P>
+<b>int pcre_dfa_exec(const pcre *<i>code</i>, const pcre_extra *<i>extra</i>,</b>
+<b> const char *<i>subject</i>, int <i>length</i>, int <i>startoffset</i>,</b>
+<b> int <i>options</i>, int *<i>ovector</i>, int <i>ovecsize</i>,</b>
+<b> int *<i>workspace</i>, int <i>wscount</i>);</b>
+</P>
+<P>
+The function <b>pcre_dfa_exec()</b> is called to match a subject string against
+a compiled pattern, using a matching algorithm that scans the subject string
+just once, and does not backtrack. This has different characteristics to the
+normal algorithm, and is not compatible with Perl. Some of the features of PCRE
+patterns are not supported. Nevertheless, there are times when this kind of
+matching can be useful. For a discussion of the two matching algorithms, and a
+list of features that <b>pcre_dfa_exec()</b> does not support, see the
+<a href="pcrematching.html"><b>pcrematching</b></a>
+documentation.
+</P>
+<P>
+The arguments for the <b>pcre_dfa_exec()</b> function are the same as for
+<b>pcre_exec()</b>, plus two extras. The <i>ovector</i> argument is used in a
+different way, and this is described below. The other common arguments are used
+in the same way as for <b>pcre_exec()</b>, so their description is not repeated
+here.
+</P>
+<P>
+The two additional arguments provide workspace for the function. The workspace
+vector should contain at least 20 elements. It is used for keeping track of
+multiple paths through the pattern tree. More workspace will be needed for
+patterns and subjects where there are a lot of potential matches.
+</P>
+<P>
+Here is an example of a simple call to <b>pcre_dfa_exec()</b>:
+<pre>
+ int rc;
+ int ovector[10];
+ int wspace[20];
+ rc = pcre_dfa_exec(
+ re, /* result of pcre_compile() */
+ NULL, /* we didn't study the pattern */
+ "some string", /* the subject string */
+ 11, /* the length of the subject string */
+ 0, /* start at offset 0 in the subject */
+ 0, /* default options */
+ ovector, /* vector of integers for substring information */
+ 10, /* number of elements (NOT size in bytes) */
+ wspace, /* working space vector */
+ 20); /* number of elements (NOT size in bytes) */
+</PRE>
+</P>
+<br><b>
+Option bits for <b>pcre_dfa_exec()</b>
+</b><br>
+<P>
+The unused bits of the <i>options</i> argument for <b>pcre_dfa_exec()</b> must be
+zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_<i>xxx</i>,
+PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
+PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF, PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE,
+PCRE_PARTIAL_HARD, PCRE_PARTIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART.
+All but the last four of these are exactly the same as for <b>pcre_exec()</b>,
+so their description is not repeated here.
+<pre>
+ PCRE_PARTIAL_HARD
+ PCRE_PARTIAL_SOFT
+</pre>
+These have the same general effect as they do for <b>pcre_exec()</b>, but the
+details are slightly different. When PCRE_PARTIAL_HARD is set for
+<b>pcre_dfa_exec()</b>, it returns PCRE_ERROR_PARTIAL if the end of the subject
+is reached and there is still at least one matching possibility that requires
+additional characters. This happens even if some complete matches have also
+been found. When PCRE_PARTIAL_SOFT is set, the return code PCRE_ERROR_NOMATCH
+is converted into PCRE_ERROR_PARTIAL if the end of the subject is reached,
+there have been no complete matches, but there is still at least one matching
+possibility. The portion of the string that was inspected when the longest
+partial match was found is set as the first matching string in both cases.
+There is a more detailed discussion of partial and multi-segment matching, with
+examples, in the
+<a href="pcrepartial.html"><b>pcrepartial</b></a>
+documentation.
+<pre>
+ PCRE_DFA_SHORTEST
+</pre>
+Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
+soon as it has found one match. Because of the way the alternative algorithm
+works, this is necessarily the shortest possible match at the first possible
+matching point in the subject string.
+<pre>
+ PCRE_DFA_RESTART
+</pre>
+When <b>pcre_dfa_exec()</b> returns a partial match, it is possible to call it
+again, with additional subject characters, and have it continue with the same
+match. The PCRE_DFA_RESTART option requests this action; when it is set, the
+<i>workspace</i> and <i>wscount</i> options must reference the same vector as
+before because data about the match so far is left in them after a partial
+match. There is more discussion of this facility in the
+<a href="pcrepartial.html"><b>pcrepartial</b></a>
+documentation.
+</P>
+<br><b>
+Successful returns from <b>pcre_dfa_exec()</b>
+</b><br>
+<P>
+When <b>pcre_dfa_exec()</b> succeeds, it may have matched more than one
+substring in the subject. Note, however, that all the matches from one run of
+the function start at the same point in the subject. The shorter matches are
+all initial substrings of the longer matches. For example, if the pattern
+<pre>
+ &#60;.*&#62;
+</pre>
+is matched against the string
+<pre>
+ This is &#60;something&#62; &#60;something else&#62; &#60;something further&#62; no more
+</pre>
+the three matched strings are
+<pre>
+ &#60;something&#62;
+ &#60;something&#62; &#60;something else&#62;
+ &#60;something&#62; &#60;something else&#62; &#60;something further&#62;
+</pre>
+On success, the yield of the function is a number greater than zero, which is
+the number of matched substrings. The substrings themselves are returned in
+<i>ovector</i>. Each string uses two elements; the first is the offset to the
+start, and the second is the offset to the end. In fact, all the strings have
+the same start offset. (Space could have been saved by giving this only once,
+but it was decided to retain some compatibility with the way <b>pcre_exec()</b>
+returns data, even though the meaning of the strings is different.)
+</P>
+<P>
+The strings are returned in reverse order of length; that is, the longest
+matching string is given first. If there were too many matches to fit into
+<i>ovector</i>, the yield of the function is zero, and the vector is filled with
+the longest matches. Unlike <b>pcre_exec()</b>, <b>pcre_dfa_exec()</b> can use
+the entire <i>ovector</i> for returning matched strings.
+</P>
+<P>
+NOTE: PCRE's "auto-possessification" optimization usually applies to character
+repeats at the end of a pattern (as well as internally). For example, the
+pattern "a\d+" is compiled as if it were "a\d++" because there is no point
+even considering the possibility of backtracking into the repeated digits. For
+DFA matching, this means that only one possible match is found. If you really
+do want multiple matches in such cases, either use an ungreedy repeat
+("a\d+?") or set the PCRE_NO_AUTO_POSSESS option when compiling.
+</P>
+<br><b>
+Error returns from <b>pcre_dfa_exec()</b>
+</b><br>
+<P>
+The <b>pcre_dfa_exec()</b> function returns a negative number when it fails.
+Many of the errors are the same as for <b>pcre_exec()</b>, and these are
+described
+<a href="#errorlist">above.</a>
+There are in addition the following errors that are specific to
+<b>pcre_dfa_exec()</b>:
+<pre>
+ PCRE_ERROR_DFA_UITEM (-16)
+</pre>
+This return is given if <b>pcre_dfa_exec()</b> encounters an item in the pattern
+that it does not support, for instance, the use of \C or a back reference.
+<pre>
+ PCRE_ERROR_DFA_UCOND (-17)
+</pre>
+This return is given if <b>pcre_dfa_exec()</b> encounters a condition item that
+uses a back reference for the condition, or a test for recursion in a specific
+group. These are not supported.
+<pre>
+ PCRE_ERROR_DFA_UMLIMIT (-18)
+</pre>
+This return is given if <b>pcre_dfa_exec()</b> is called with an <i>extra</i>
+block that contains a setting of the <i>match_limit</i> or
+<i>match_limit_recursion</i> fields. This is not supported (these fields are
+meaningless for DFA matching).
+<pre>
+ PCRE_ERROR_DFA_WSSIZE (-19)
+</pre>
+This return is given if <b>pcre_dfa_exec()</b> runs out of space in the
+<i>workspace</i> vector.
+<pre>
+ PCRE_ERROR_DFA_RECURSE (-20)
+</pre>
+When a recursive subpattern is processed, the matching function calls itself
+recursively, using private vectors for <i>ovector</i> and <i>workspace</i>. This
+error is given if the output vector is not large enough. This should be
+extremely rare, as a vector of size 1000 is used.
+<pre>
+ PCRE_ERROR_DFA_BADRESTART (-30)
+</pre>
+When <b>pcre_dfa_exec()</b> is called with the <b>PCRE_DFA_RESTART</b> option,
+some plausibility checks are made on the contents of the workspace, which
+should contain data about the previous partial match. If any of these checks
+fail, this error is given.
+</P>
+<br><a name="SEC24" href="#TOC1">SEE ALSO</a><br>
+<P>
+<b>pcre16</b>(3), <b>pcre32</b>(3), <b>pcrebuild</b>(3), <b>pcrecallout</b>(3),
+<b>pcrecpp(3)</b>(3), <b>pcrematching</b>(3), <b>pcrepartial</b>(3),
+<b>pcreposix</b>(3), <b>pcreprecompile</b>(3), <b>pcresample</b>(3),
+<b>pcrestack</b>(3).
+</P>
+<br><a name="SEC25" href="#TOC1">AUTHOR</a><br>
+<P>
+Philip Hazel
+<br>
+University Computing Service
+<br>
+Cambridge CB2 3QH, England.
+<br>
+</P>
+<br><a name="SEC26" href="#TOC1">REVISION</a><br>
+<P>
+Last updated: 18 December 2015
+<br>
+Copyright &copy; 1997-2015 University of Cambridge.
+<br>
+<p>
+Return to the <a href="index.html">PCRE index page</a>.
+</p>