/[pcre]/code/trunk/doc/html/pcre.html

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-revision 75 by nigel,
Sat Feb 24 21:40:37 2007 UTC
+revision 91 by nigel,
Sat Feb 24 21:41:34 2007 UTC
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 man page, in case the conversion went wr
  <P>
  The PCRE library is a set of functions that implement regular expression
  pattern matching using the same syntax and semantics as Perl, with just a few
- differences. The current implementation of PCRE (release 5.x) corresponds
+ differences. The current implementation of PCRE (release 6.x) corresponds
  approximately with Perl 5.8, including support for UTF-8 encoded strings and
  Unicode general category properties. However, this support has to be explicitly
  enabled; it is not the default.
  </P>
  <P>
+ In addition to the Perl-compatible matching function, PCRE also contains an
+ alternative matching function that matches the same compiled patterns in a
+ different way. In certain circumstances, the alternative function has some
+ advantages. For a discussion of the two matching algorithms, see the
+ <a href="pcrematching.html"><b>pcrematching</b></a>
+ page.
+ </P>
+ <P>
  PCRE is written in C and released as a C library. A number of people have
- written wrappers and interfaces of various kinds. A C++ class is included in
+ written wrappers and interfaces of various kinds. In particular, Google Inc.
- these contributions, which can be found in the <i>Contrib</i> directory at the
+ have provided a comprehensive C++ wrapper. This is now included as part of the
- primary FTP site, which is:
+ PCRE distribution. The
+ <a href="pcrecpp.html"><b>pcrecpp</b></a>
+ page has details of this interface. Other people's contributions can be found
+ in the <i>Contrib</i> directory at the primary FTP site, which is:
  <a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre</a>
  </P>
  <P>
-Line 53 
 available. The features themselves are d
+Line 64 
 available. The features themselves are d
  page. Documentation about building PCRE for various operating systems can be
  found in the <b>README</b> file in the source distribution.
  </P>
+ <P>
+ The library contains a number of undocumented internal functions and data
+ tables that are used by more than one of the exported external functions, but
+ which are not intended for use by external callers. Their names all begin with
+ "_pcre_", which hopefully will not provoke any name clashes. In some
+ environments, it is possible to control which external symbols are exported
+ when a shared library is built, and in these cases the undocumented symbols are
+ not exported.
+ </P>
  <br><a name="SEC2" href="#TOC1">USER DOCUMENTATION</a><br>
  <P>
  The user documentation for PCRE comprises a number of different sections. In
-Line 62 
 all the sections are concatenated, for e
+Line 82 
 all the sections are concatenated, for e
  follows:
  <pre>
    pcre              this document
-   pcreapi           details of PCRE's native API
+   pcreapi           details of PCRE's native C API
    pcrebuild         options for building PCRE
    pcrecallout       details of the callout feature
    pcrecompat        discussion of Perl compatibility
+   pcrecpp           details of the C++ wrapper
    pcregrep          description of the <b>pcregrep</b> command
+   pcrematching      discussion of the two matching algorithms
    pcrepartial       details of the partial matching facility
    pcrepattern       syntax and semantics of supported regular expressions
    pcreperform       discussion of performance issues
-   pcreposix         the POSIX-compatible API
+   pcreposix         the POSIX-compatible C API
    pcreprecompile    details of saving and re-using precompiled patterns
    pcresample        discussion of the sample program
+   pcrestack         discussion of stack usage
    pcretest          description of the <b>pcretest</b> testing command
  </pre>
  In addition, in the "man" and HTML formats, there is a short page for each
- library function, listing its arguments and results.
+ C library function, listing its arguments and results.
  </P>
  <br><a name="SEC3" href="#TOC1">LIMITATIONS</a><br>
  <P>
-Line 94 
 documentation for details). In these cas
+Line 117 
 documentation for details). In these cas
  However, the speed of execution will be slower.
  </P>
  <P>
- All values in repeating quantifiers must be less than 65536.
+ All values in repeating quantifiers must be less than 65536. The maximum
- The maximum number of capturing subpatterns is 65535.
+ compiled length of subpattern with an explicit repeat count is 30000 bytes. The
+ maximum number of capturing subpatterns is 65535.
  </P>
  <P>
  There is no limit to the number of non-capturing subpatterns, but the maximum
-Line 103 
 depth of nesting of all kinds of parenth
+Line 127 
 depth of nesting of all kinds of parenth
  subpatterns, assertions, and other types of subpattern, is 200.
  </P>
  <P>
+ The maximum length of name for a named subpattern is 32, and the maximum number
+ of named subpatterns is 10000.
+ </P>
+ <P>
  The maximum length of a subject string is the largest positive number that an
- integer variable can hold. However, PCRE uses recursion to handle subpatterns
+ integer variable can hold. However, when using the traditional matching
- and indefinite repetition. This means that the available stack space may limit
+ function, PCRE uses recursion to handle subpatterns and indefinite repetition.
- the size of a subject string that can be processed by certain patterns.
+ This means that the available stack space may limit the size of a subject
+ string that can be processed by certain patterns. For a discussion of stack
+ issues, see the
+ <a href="pcrestack.html"><b>pcrestack</b></a>
+ documentation.
  <a name="utf8support"></a></P>
  <br><a name="SEC4" href="#TOC1">UTF-8 AND UNICODE PROPERTY SUPPORT</a><br>
  <P>
-Line 133 
 If PCRE is built with Unicode character
+Line 165 
 If PCRE is built with Unicode character
  support), the escape sequences \p{..}, \P{..}, and \X are supported.
  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. A full list is given in the
+ number, the Unicode script names such as Arabic or Han, and the derived
+ properties Any and L&. A full list is given in the
  <a href="pcrepattern.html"><b>pcrepattern</b></a>
- documentation. The PCRE library is increased in size by about 90K when Unicode
+ documentation. Only the short names for properties are supported. For example,
- property support is included.
+ \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.
  </P>
  <P>
  The following comments apply when PCRE is running in UTF-8 mode:
-Line 154 
 PCRE when PCRE_NO_UTF8_CHECK is set, the
+Line 189 
 PCRE when PCRE_NO_UTF8_CHECK is set, the
  may crash.
  </P>
  <P>
-. In a pattern, the escape sequence \x{...}, where the contents of the braces
+. An unbraced hexadecimal escape sequence (such as \xb3) matches a two-byte
- is a string of hexadecimal digits, is interpreted as a UTF-8 character whose
+ UTF-8 character if the value is greater than 127.
- code number is the given hexadecimal number, for example: \x{1234}. If a
- non-hexadecimal digit appears between the braces, the item is not recognized.
- This escape sequence can be used either as a literal, or within a character
- class.
  </P>
  <P>
-. The original hexadecimal escape sequence, \xhh, matches a two-byte UTF-8
+. Octal numbers up to \777 are recognized, and match two-byte UTF-8
- character if the value is greater than 127.
+ characters for values greater than \177.
  </P>
  <P>
 . Repeat quantifiers apply to complete UTF-8 characters, not to individual
-Line 174 
 bytes, for example: \x{100}{3}.
+Line 205 
 bytes, for example: \x{100}{3}.
  </P>
  <P>
 . The escape sequence \C can be used to match a single byte in UTF-8 mode,
- but its use can lead to some strange effects.
+ but its use can lead to some strange effects. This facility is not available in
+ the alternative matching function, <b>pcre_dfa_exec()</b>.
  </P>
  <P>
 . The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
-Line 195 
 than 128, unless PCRE is built with Unic
+Line 227 
 than 128, unless PCRE is built with Unic
  property support is available, PCRE still uses its own character tables when
  checking the case of low-valued characters, so as not to degrade performance.
  The Unicode property information is used only for characters with higher
- values.
+ values. Even when Unicode property support is available, PCRE supports
+ case-insensitive matching only when there is a one-to-one mapping between a
+ letter's cases. There are a small number of many-to-one mappings in Unicode;
+ these are not supported by PCRE.
  </P>
  <br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
  <P>
- Philip Hazel &#60;ph10@cam.ac.uk&#62;
+ Philip Hazel
  <br>
  University Computing Service,
  <br>
  Cambridge CB2 3QG, England.
+ </P>
+ <P>
+ Putting an actual email address here seems to have been a spam magnet, so I've
+ taken it away. If you want to email me, use my initial and surname, separated
+ by a dot, at the domain ucs.cam.ac.uk.
+ Last updated: 05 June 2006
  <br>
- Phone: +44 1223 334714
+ Copyright &copy; 1997-2006 University of Cambridge.
- Last updated: 09 September 2004
- <br>
- Copyright &copy; 1997-2004 University of Cambridge.
  <p>
  Return to the <a href="index.html">PCRE index page</a>.
  </p>

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