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    1 <html>
    2 <head>
    3 <title>pcrelimits specification</title>
    4 </head>
    5 <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
    6 <h1>pcrelimits man page</h1>
    7 <p>
    8 Return to the <a href="index.html">PCRE index page</a>.
    9 </p>
   10 <p>
   11 This page is part of the PCRE HTML documentation. It was generated automatically
   12 from the original man page. If there is any nonsense in it, please consult the
   13 man page, in case the conversion went wrong.
   14 <br>
   15 <br><b>
   16 SIZE AND OTHER LIMITATIONS
   17 </b><br>
   18 <P>
   19 There are some size limitations in PCRE but it is hoped that they will never in
   20 practice be relevant.
   21 </P>
   22 <P>
   23 The maximum length of a compiled pattern is approximately 64K data units (bytes
   24 for the 8-bit library, 16-bit units for the 16-bit library, and 32-bit units for
   25 the 32-bit library) if PCRE is compiled with the default internal linkage size,
   26 which is 2 bytes for the 8-bit and 16-bit libraries, and 4 bytes for the 32-bit
   27 library. If you want to process regular expressions that are truly enormous,
   28 you can compile PCRE with an internal linkage size of 3 or 4 (when building the
   29 16-bit or 32-bit library, 3 is rounded up to 4). See the <b>README</b> file in
   30 the source distribution and the
   31 <a href="pcrebuild.html"><b>pcrebuild</b></a>
   32 documentation for details. In these cases the limit is substantially larger.
   33 However, the speed of execution is slower.
   34 </P>
   35 <P>
   36 All values in repeating quantifiers must be less than 65536.
   37 </P>
   38 <P>
   39 There is no limit to the number of parenthesized subpatterns, but there can be
   40 no more than 65535 capturing subpatterns. There is, however, a limit to the
   41 depth of nesting of parenthesized subpatterns of all kinds. This is imposed in
   42 order to limit the amount of system stack used at compile time. The limit can
   43 be specified when PCRE is built; the default is 250.
   44 </P>
   45 <P>
   46 There is a limit to the number of forward references to subsequent subpatterns
   47 of around 200,000. Repeated forward references with fixed upper limits, for
   48 example, (?2){0,100} when subpattern number 2 is to the right, are included in
   49 the count. There is no limit to the number of backward references.
   50 </P>
   51 <P>
   52 The maximum length of name for a named subpattern is 32 characters, and the
   53 maximum number of named subpatterns is 10000.
   54 </P>
   55 <P>
   56 The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or (*THEN) verb
   57 is 255 for the 8-bit library and 65535 for the 16-bit and 32-bit libraries.
   58 </P>
   59 <P>
   60 The maximum length of a subject string is the largest positive number that an
   61 integer variable can hold. However, when using the traditional matching
   62 function, PCRE uses recursion to handle subpatterns and indefinite repetition.
   63 This means that the available stack space may limit the size of a subject
   64 string that can be processed by certain patterns. For a discussion of stack
   65 issues, see the
   66 <a href="pcrestack.html"><b>pcrestack</b></a>
   67 documentation.
   68 </P>
   69 <br><b>
   70 AUTHOR
   71 </b><br>
   72 <P>
   73 Philip Hazel
   74 <br>
   75 University Computing Service
   76 <br>
   77 Cambridge CB2 3QH, England.
   78 <br>
   79 </P>
   80 <br><b>
   81 REVISION
   82 </b><br>
   83 <P>
   84 Last updated: 05 November 2013
   85 <br>
   86 Copyright &copy; 1997-2013 University of Cambridge.
   87 <br>
   88 <p>
   89 Return to the <a href="index.html">PCRE index page</a>.
   90 </p>