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

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-revision 75 by nigel,
Sat Feb 24 21:40:37 2007 UTC
+revision 197 by ph10,
Tue Jul 31 10:50:18 2007 UTC
 Line 18 
 man page, in case the conversion went wr
  <li><a name="TOC3" href="#SEC3">LIMITATIONS</a>
  <li><a name="TOC4" href="#SEC4">UTF-8 AND UNICODE PROPERTY SUPPORT</a>
  <li><a name="TOC5" href="#SEC5">AUTHOR</a>
+ <li><a name="TOC6" href="#SEC6">REVISION</a>
  </ul>
  <br><a name="SEC1" href="#TOC1">INTRODUCTION</a><br>
  <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. (Certain features that appeared in Python and PCRE before they
- approximately with Perl 5.8, including support for UTF-8 encoded strings and
+ appeared in Perl are also available using the Python syntax.)
- Unicode general category properties. However, this support has to be explicitly
+ </P>
- enabled; it is not the default.
+ <P>
+ The current implementation of PCRE (release 7.x) corresponds approximately with
+ Perl 5.10, including support for UTF-8 encoded strings and Unicode general
+ category properties. However, UTF-8 and Unicode support has to be explicitly
+ enabled; it is not the default. The Unicode tables correspond to Unicode
+ release 5.0.0.
+ </P>
+ <P>
+ In addition to the Perl-compatible matching function, PCRE 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 70 
 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 88 
 all the sections are concatenated, for e
  follows:
  <pre>
    pcre              this document
-   pcreapi           details of PCRE's native API
+   pcre-config       show PCRE installation configuration information
+   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 91 
 internal linkage size of 3 or 4 (see the
+Line 121 
 internal linkage size of 3 or 4 (see the
  distribution and the
  <a href="pcrebuild.html"><b>pcrebuild</b></a>
  documentation for details). In these cases the limit is substantially larger.
- However, the speed of execution will be slower.
+ However, the speed of execution is slower.
+ </P>
+ <P>
+ All values in repeating quantifiers must be less than 65536. The maximum
+ 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 parenthesized subpatterns, but there can be
+ no more than 65535 capturing subpatterns.
  </P>
  <P>
- All values in repeating quantifiers must be less than 65536.
+ If a non-capturing subpattern with an unlimited repetition quantifier can match
- The maximum number of capturing subpatterns is 65535.
+ an empty string, there is a limit of 1000 on the number of times it can be
+ repeated while not matching an empty string - if it does match an empty
+ string, the loop is immediately broken.
  </P>
  <P>
- There is no limit to the number of non-capturing subpatterns, but the maximum
+ The maximum length of name for a named subpattern is 32 characters, and the
- depth of nesting of all kinds of parenthesized subpattern, including capturing
+ maximum number of named subpatterns is 10000.
- subpatterns, assertions, and other types of subpattern, is 200.
  </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 126 
 instead of just strings of bytes.
+Line 170 
 instead of just strings of bytes.
  <P>
  If you compile PCRE with UTF-8 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_UTF8 flag in several places, so should not be very large.
+ to testing the PCRE_UTF8 flag occasionally, so should not be very big.
  </P>
  <P>
  If PCRE is built with Unicode character property support (which implies UTF-8
  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 201 
 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 217 
 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 190 
 must use Unicode property tests such as
+Line 234 
 must use Unicode property tests such as
  low-valued characters.
  </P>
  <P>
-. Case-insensitive matching applies only to characters whose values are less
+. However, the Perl 5.10 horizontal and vertical whitespace matching escapes
+ (\h, \H, \v, and \V) do match all the appropriate Unicode characters.
+ </P>
+ <P>
+. Case-insensitive matching applies only to characters whose values are less
  than 128, unless PCRE is built with Unicode property support. Even when Unicode
  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,
+ University Computing Service
  <br>
- Cambridge CB2 3QG, England.
+ Cambridge CB2 3QH, England.
+ <br>
+ </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 two initials, followed by the
+ two digits 10, at the domain cam.ac.uk.
+ </P>
+ <br><a name="SEC6" href="#TOC1">REVISION</a><br>
+ <P>
+ Last updated: 30 July 2007
  <br>
- Phone: +44 1223 334714
+ Copyright &copy; 1997-2007 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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