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PCREUNICODE(3)             Library Functions Manual             PCREUNICODE(3)

NAME
       PCRE - Perl-compatible regular expressions
UTF-8, UTF-16, UTF-32, AND UNICODE PROPERTY SUPPORT
       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
       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
       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
       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
       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 rel-
       evant functions. The entire string is checked before any other process-
       ing takes place. From release 7.3 of PCRE, the check is  according  the
       rules of RFC 3629, which are themselves derived from the Unicode speci-
       fication. 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,  exclud-
       ing the surrogate area and the non-characters.
       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.)
       Also excluded are the "Non-Character" code points, which are U+FDD0  to
       U+FDEF  and  the  last  two  code  points  in  each plane, U+??FFFE and
       U+??FFFF.
       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  perfor-
       mance,  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 valid-
       ity  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.
       Excluded  are  the  "Non-Character"  code  points,  which are U+FDD0 to
       U+FDEF and the last  two  code  points  in  each  plane,  U+??FFFE  and
       U+??FFFF.
       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 perfor-
       mance. 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 (respec-
       tively) 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 valid-
       ity 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, and the "Non-Character" code points, which are U+FDD0 to U+FDEF
       and the last two characters in each plane, U+??FFFE and U+??FFFF.
       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 perfor-
       mance. 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 (respec-
       tively) 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 individ-
       ual 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 sec-
       tion 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 code-
       points 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
       Philip Hazel
       University Computing Service
       Cambridge CB2 3QH, England.
REVISION
       Last updated: 11 November 2012
       Copyright (c) 1997-2012 University of Cambridge.

PCRE 8.32                      11 November 2012                 PCREUNICODE(3)