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diff --git a/doc/pcreunicode.3 b/doc/pcreunicode.3 new file mode 100644 index 0000000..cb5e526 --- /dev/null +++ b/doc/pcreunicode.3 @@ -0,0 +1,249 @@ +.TH PCREUNICODE 3 "27 February 2013" "PCRE 8.33" +.SH NAME +PCRE - Perl-compatible regular expressions +.SH "UTF-8, UTF-16, UTF-32, AND UNICODE PROPERTY SUPPORT" +.rs +.sp +As well as UTF-8 support, PCRE also supports UTF-16 (from release 8.30) and +UTF-32 (from release 8.32), by means of two additional libraries. They can be +built as well as, or instead of, the 8-bit library. +. +. +.SH "UTF-8 SUPPORT" +.rs +.sp +In order process UTF-8 strings, you must build PCRE's 8-bit library with UTF +support, and, in addition, you must call +.\" HREF +\fBpcre_compile()\fP +.\" +with the PCRE_UTF8 option flag, or the pattern must start with the sequence +(*UTF8) or (*UTF). When either of these is the case, both the pattern and any +subject strings that are matched against it are treated as UTF-8 strings +instead of strings of individual 1-byte characters. +. +. +.SH "UTF-16 AND UTF-32 SUPPORT" +.rs +.sp +In order process UTF-16 or UTF-32 strings, you must build PCRE's 16-bit or +32-bit library with UTF support, and, in addition, you must call +.\" HREF +\fBpcre16_compile()\fP +.\" +or +.\" HREF +\fBpcre32_compile()\fP +.\" +with the PCRE_UTF16 or PCRE_UTF32 option flag, as appropriate. Alternatively, +the pattern must start with the sequence (*UTF16), (*UTF32), as appropriate, or +(*UTF), which can be used with either library. When UTF mode is set, both the +pattern and any subject strings that are matched against it are treated as +UTF-16 or UTF-32 strings instead of strings of individual 16-bit or 32-bit +characters. +. +. +.SH "UTF SUPPORT OVERHEAD" +.rs +.sp +If you compile PCRE with UTF support, but do not use it at run time, the +library will be a bit bigger, but the additional run time overhead is limited +to testing the PCRE_UTF[8|16|32] flag occasionally, so should not be very big. +. +. +.SH "UNICODE PROPERTY SUPPORT" +.rs +.sp +If PCRE is built with Unicode character property support (which implies UTF +support), the escape sequences \ep{..}, \eP{..}, and \eX can be used. +The available properties that can be tested are limited to the general +category properties such as Lu for an upper case letter or Nd for a decimal +number, the Unicode script names such as Arabic or Han, and the derived +properties Any and L&. Full lists is given in the +.\" HREF +\fBpcrepattern\fP +.\" +and +.\" HREF +\fBpcresyntax\fP +.\" +documentation. Only the short names for properties are supported. For example, +\ep{L} matches a letter. Its Perl synonym, \ep{Letter}, is not supported. +Furthermore, in Perl, many properties may optionally be prefixed by "Is", for +compatibility with Perl 5.6. PCRE does not support this. +. +. +.\" HTML <a name="utf8strings"></a> +.SS "Validity of UTF-8 strings" +.rs +.sp +When you set the PCRE_UTF8 flag, the byte strings passed as patterns and +subjects are (by default) checked for validity on entry to the relevant +functions. The entire string is checked before any other processing takes +place. From release 7.3 of PCRE, the check is according the rules of RFC 3629, +which are themselves derived from the Unicode specification. Earlier releases +of PCRE followed the rules of RFC 2279, which allows the full range of 31-bit +values (0 to 0x7FFFFFFF). The current check allows only values in the range U+0 +to U+10FFFF, excluding the surrogate area. (From release 8.33 the so-called +"non-character" code points are no longer excluded because Unicode corrigendum +#9 makes it clear that they should not be.) +.P +Characters in the "Surrogate Area" of Unicode are reserved for use by UTF-16, +where they are used in pairs to encode codepoints with values greater than +0xFFFF. The code points that are encoded by UTF-16 pairs are available +independently in the UTF-8 and UTF-32 encodings. (In other words, the whole +surrogate thing is a fudge for UTF-16 which unfortunately messes up UTF-8 and +UTF-32.) +.P +If an invalid UTF-8 string is passed to PCRE, an error return is given. At +compile time, the only additional information is the offset to the first byte +of the failing character. The run-time functions \fBpcre_exec()\fP and +\fBpcre_dfa_exec()\fP also pass back this information, as well as a more +detailed reason code if the caller has provided memory in which to do this. +.P +In some situations, you may already know that your strings are valid, and +therefore want to skip these checks in order to improve performance, for +example in the case of a long subject string that is being scanned repeatedly. +If you set the PCRE_NO_UTF8_CHECK flag at compile time or at run time, PCRE +assumes that the pattern or subject it is given (respectively) contains only +valid UTF-8 codes. In this case, it does not diagnose an invalid UTF-8 string. +.P +Note that passing PCRE_NO_UTF8_CHECK to \fBpcre_compile()\fP just disables the +check for the pattern; it does not also apply to subject strings. If you want +to disable the check for a subject string you must pass this option to +\fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP. +.P +If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, the result +is undefined and your program may crash. +. +. +.\" HTML <a name="utf16strings"></a> +.SS "Validity of UTF-16 strings" +.rs +.sp +When you set the PCRE_UTF16 flag, the strings of 16-bit data units that are +passed as patterns and subjects are (by default) checked for validity on entry +to the relevant functions. Values other than those in the surrogate range +U+D800 to U+DFFF are independent code points. Values in the surrogate range +must be used in pairs in the correct manner. +.P +If an invalid UTF-16 string is passed to PCRE, an error return is given. At +compile time, the only additional information is the offset to the first data +unit of the failing character. The run-time functions \fBpcre16_exec()\fP and +\fBpcre16_dfa_exec()\fP also pass back this information, as well as a more +detailed reason code if the caller has provided memory in which to do this. +.P +In some situations, you may already know that your strings are valid, and +therefore want to skip these checks in order to improve performance. If you set +the PCRE_NO_UTF16_CHECK flag at compile time or at run time, PCRE assumes that +the pattern or subject it is given (respectively) contains only valid UTF-16 +sequences. In this case, it does not diagnose an invalid UTF-16 string. +However, if an invalid string is passed, the result is undefined. +. +. +.\" HTML <a name="utf32strings"></a> +.SS "Validity of UTF-32 strings" +.rs +.sp +When you set the PCRE_UTF32 flag, the strings of 32-bit data units that are +passed as patterns and subjects are (by default) checked for validity on entry +to the relevant functions. This check allows only values in the range U+0 +to U+10FFFF, excluding the surrogate area U+D800 to U+DFFF. +.P +If an invalid UTF-32 string is passed to PCRE, an error return is given. At +compile time, the only additional information is the offset to the first data +unit of the failing character. The run-time functions \fBpcre32_exec()\fP and +\fBpcre32_dfa_exec()\fP also pass back this information, as well as a more +detailed reason code if the caller has provided memory in which to do this. +.P +In some situations, you may already know that your strings are valid, and +therefore want to skip these checks in order to improve performance. If you set +the PCRE_NO_UTF32_CHECK flag at compile time or at run time, PCRE assumes that +the pattern or subject it is given (respectively) contains only valid UTF-32 +sequences. In this case, it does not diagnose an invalid UTF-32 string. +However, if an invalid string is passed, the result is undefined. +. +. +.SS "General comments about UTF modes" +.rs +.sp +1. Codepoints less than 256 can be specified in patterns by either braced or +unbraced hexadecimal escape sequences (for example, \ex{b3} or \exb3). Larger +values have to use braced sequences. +.P +2. Octal numbers up to \e777 are recognized, and in UTF-8 mode they match +two-byte characters for values greater than \e177. +.P +3. Repeat quantifiers apply to complete UTF characters, not to individual +data units, for example: \ex{100}{3}. +.P +4. The dot metacharacter matches one UTF character instead of a single data +unit. +.P +5. The escape sequence \eC can be used to match a single byte in UTF-8 mode, or +a single 16-bit data unit in UTF-16 mode, or a single 32-bit data unit in +UTF-32 mode, but its use can lead to some strange effects because it breaks up +multi-unit characters (see the description of \eC in the +.\" HREF +\fBpcrepattern\fP +.\" +documentation). The use of \eC is not supported in the alternative matching +function \fBpcre[16|32]_dfa_exec()\fP, nor is it supported in UTF mode by the +JIT optimization of \fBpcre[16|32]_exec()\fP. If JIT optimization is requested +for a UTF pattern that contains \eC, it will not succeed, and so the matching +will be carried out by the normal interpretive function. +.P +6. The character escapes \eb, \eB, \ed, \eD, \es, \eS, \ew, and \eW correctly +test characters of any code value, but, by default, the characters that PCRE +recognizes as digits, spaces, or word characters remain the same set as in +non-UTF mode, all with values less than 256. This remains true even when PCRE +is built to include Unicode property support, because to do otherwise would +slow down PCRE in many common cases. Note in particular that this applies to +\eb and \eB, because they are defined in terms of \ew and \eW. If you really +want to test for a wider sense of, say, "digit", you can use explicit Unicode +property tests such as \ep{Nd}. Alternatively, if you set the PCRE_UCP option, +the way that the character escapes work is changed so that Unicode properties +are used to determine which characters match. There are more details in the +section on +.\" HTML <a href="pcrepattern.html#genericchartypes"> +.\" </a> +generic character types +.\" +in the +.\" HREF +\fBpcrepattern\fP +.\" +documentation. +.P +7. Similarly, characters that match the POSIX named character classes are all +low-valued characters, unless the PCRE_UCP option is set. +.P +8. However, the horizontal and vertical white space matching escapes (\eh, \eH, +\ev, and \eV) do match all the appropriate Unicode characters, whether or not +PCRE_UCP is set. +.P +9. Case-insensitive matching applies only to characters whose values are less +than 128, unless PCRE is built with Unicode property support. A few Unicode +characters such as Greek sigma have more than two codepoints that are +case-equivalent. Up to and including PCRE release 8.31, only one-to-one case +mappings were supported, but later releases (with Unicode property support) do +treat as case-equivalent all versions of characters such as Greek sigma. +. +. +.SH AUTHOR +.rs +.sp +.nf +Philip Hazel +University Computing Service +Cambridge CB2 3QH, England. +.fi +. +. +.SH REVISION +.rs +.sp +.nf +Last updated: 27 February 2013 +Copyright (c) 1997-2013 University of Cambridge. +.fi |