NAME | UTF-8, UTF-16, UTF-32, AND UNICODE PROPERTY SUPPORT | UTF-8 SUPPORT | UTF-16 AND UTF-32 SUPPORT | UTF SUPPORT OVERHEAD | UNICODE PROPERTY SUPPORT | AUTHOR | REVISION | COLOPHON

PCREUNICODE(3)            Library Functions Manual            PCREUNICODE(3)

NAME         top

       PCRE - Perl-compatible regular expressions

UTF-8, UTF-16, UTF-32, AND UNICODE PROPERTY SUPPORT         top


       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.

UTF-8 SUPPORT         top


       In order process UTF-8 strings, you must build PCRE's 8-bit library
       with UTF support, and, in addition, you must call pcre_compile() 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.

UTF-16 AND UTF-32 SUPPORT         top


       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 pcre16_compile() or pcre32_compile() 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.

UTF SUPPORT OVERHEAD         top


       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.

UNICODE PROPERTY SUPPORT         top


       If PCRE is built with Unicode character property support (which
       implies UTF support), the escape sequences \p{..}, \P{..}, and \X 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 pcrepattern and pcresyntax documentation. Only the short names
       for properties are supported. For example, \p{L} matches a letter.
       Its Perl synonym, \p{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.

   Validity of UTF-8 strings

       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.)

       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.)

       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
       pcre_exec() and pcre_dfa_exec() also pass back this information, as
       well as a more detailed reason code if the caller has provided memory
       in which to do this.

       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.

       Note that passing PCRE_NO_UTF8_CHECK to pcre_compile() 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 pcre_exec() or pcre_dfa_exec().

       If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set,
       the result is undefined and your program may crash.

   Validity of UTF-16 strings

       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.

       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 pcre16_exec() and pcre16_dfa_exec() also pass back this
       information, as well as a more detailed reason code if the caller has
       provided memory in which to do this.

       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.

   Validity of UTF-32 strings

       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.

       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 pcre32_exec() and pcre32_dfa_exec() also pass back this
       information, as well as a more detailed reason code if the caller has
       provided memory in which to do this.

       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.

   General comments about UTF modes

       1. Codepoints less than 256 can be specified in patterns by either
       braced or unbraced hexadecimal escape sequences (for example, \x{b3}
       or \xb3). Larger values have to use braced sequences.

       2. Octal numbers up to \777 are recognized, and in UTF-8 mode they
       match two-byte characters for values greater than \177.

       3. Repeat quantifiers apply to complete UTF characters, not to
       individual data units, for example: \x{100}{3}.

       4. The dot metacharacter matches one UTF character instead of a
       single data unit.

       5. The escape sequence \C 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 \C in the pcrepattern documentation). The use of \C is
       not supported in the alternative matching function
       pcre[16|32]_dfa_exec(), nor is it supported in UTF mode by the JIT
       optimization of pcre[16|32]_exec(). If JIT optimization is requested
       for a UTF pattern that contains \C, it will not succeed, and so the
       matching will be carried out by the normal interpretive function.

       6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W 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 \b and \B, because
       they are defined in terms of \w and \W. If you really want to test
       for a wider sense of, say, "digit", you can use explicit Unicode
       property tests such as \p{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 generic character types in
       the pcrepattern documentation.

       7. Similarly, characters that match the POSIX named character classes
       are all low-valued characters, unless the PCRE_UCP option is set.

       8. However, the horizontal and vertical white space matching escapes
       (\h, \H, \v, and \V) do match all the appropriate Unicode characters,
       whether or not PCRE_UCP is set.

       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.

AUTHOR         top


       Philip Hazel
       University Computing Service
       Cambridge CB2 3QH, England.

REVISION         top


       Last updated: 27 February 2013
       Copyright (c) 1997-2013 University of Cambridge.

COLOPHON         top

       This page is part of the PCRE (Perl Compatible Regular Expressions)
       project.  Information about the project can be found at 
       ⟨http://www.pcre.org/⟩.  If you have a bug report for this manual
       page, see ⟨http://bugs.exim.org/enter_bug.cgi?product=PCRE⟩.  This
       page was obtained from the tarball pcre-8.41.tar.gz fetched from 
       ⟨ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/⟩ on
       2017-09-15.  If you discover any rendering problems in this HTML ver‐
       sion of the page, or you believe there is a better or more up-to-date
       source for the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original man‐
       ual page), send a mail to man-pages@man7.org

PCRE 8.33                     27 February 2013                PCREUNICODE(3)