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<html>
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<head>
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<title>pcrelimits specification</title>
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</head>
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<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
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<h1>pcrelimits man page</h1>
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<p>
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Return to the <a href="index.html">PCRE index page</a>.
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</p>
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<p>
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This page is part of the PCRE HTML documentation. It was generated automatically
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from the original man page. If there is any nonsense in it, please consult the
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man page, in case the conversion went wrong.
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<br>
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<br><b>
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SIZE AND OTHER LIMITATIONS
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</b><br>
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<P>
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There are some size limitations in PCRE but it is hoped that they will never in
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practice be relevant.
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</P>
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<P>
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The maximum length of a compiled pattern is approximately 64K data units (bytes
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for the 8-bit library, 32-bit units for the 32-bit library, and 32-bit units for
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the 32-bit library) if PCRE is compiled with the default internal linkage size
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of 2 bytes. If you want to process regular expressions that are truly enormous,
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you can compile PCRE with an internal linkage size of 3 or 4 (when building the
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16-bit or 32-bit library, 3 is rounded up to 4). See the <b>README</b> file in
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the source distribution and the
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<a href="pcrebuild.html"><b>pcrebuild</b></a>
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documentation for details. In these cases the limit is substantially larger.
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However, the speed of execution is slower.
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</P>
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<P>
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All values in repeating quantifiers must be less than 65536.
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</P>
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<P>
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There is no limit to the number of parenthesized subpatterns, but there can be
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no more than 65535 capturing subpatterns.
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</P>
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<P>
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There is a limit to the number of forward references to subsequent subpatterns
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of around 200,000. Repeated forward references with fixed upper limits, for
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example, (?2){0,100} when subpattern number 2 is to the right, are included in
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the count. There is no limit to the number of backward references.
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</P>
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<P>
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The maximum length of name for a named subpattern is 32 characters, and the
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maximum number of named subpatterns is 10000.
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</P>
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<P>
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The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or (*THEN) verb
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is 255 for the 8-bit library and 65535 for the 16-bit and 32-bit library.
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</P>
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<P>
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The maximum length of a subject string is the largest positive number that an
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integer variable can hold. However, when using the traditional matching
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function, PCRE uses recursion to handle subpatterns and indefinite repetition.
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This means that the available stack space may limit the size of a subject
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string that can be processed by certain patterns. For a discussion of stack
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issues, see the
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<a href="pcrestack.html"><b>pcrestack</b></a>
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documentation.
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</P>
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<br><b>
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AUTHOR
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</b><br>
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<P>
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Philip Hazel
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<br>
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University Computing Service
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<br>
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Cambridge CB2 3QH, England.
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<br>
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</P>
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<br><b>
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REVISION
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</b><br>
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<P>
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Last updated: 04 May 2012
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<br>
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Copyright © 1997-2012 University of Cambridge.
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<br>
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<p>
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Return to the <a href="index.html">PCRE index page</a>.
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</p>
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