104 lines
3.5 KiB
HTML
104 lines
3.5 KiB
HTML
<html>
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<head>
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<title>pcre2limits 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>pcre2limits man page</h1>
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<p>
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Return to the <a href="index.html">PCRE2 index page</a>.
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</p>
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<p>
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This page is part of the PCRE2 HTML documentation. It was generated
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automatically from the original man page. If there is any nonsense in it,
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please consult the 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 PCRE2 but it is hoped that they will never
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in practice be relevant.
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</P>
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<P>
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The maximum size of a compiled pattern is approximately 64K code units for the
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8-bit and 16-bit libraries if PCRE2 is compiled with the default internal
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linkage size, which is 2 bytes for these libraries. If you want to process
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regular expressions that are truly enormous, you can compile PCRE2 with an
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internal linkage size of 3 or 4 (when building the 16-bit library, 3 is rounded
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up to 4). See the <b>README</b> file in the source distribution and the
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<a href="pcre2build.html"><b>pcre2build</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. In the 32-bit library, the internal
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linkage size is always 4.
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</P>
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<P>
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The maximum length of a source pattern string is essentially unlimited; it is
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the largest number a PCRE2_SIZE variable can hold. However, the program that
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calls <b>pcre2_compile()</b> can specify a smaller limit.
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</P>
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<P>
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The maximum length (in code units) of a subject string is one less than the
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largest number a PCRE2_SIZE variable can hold. PCRE2_SIZE is an unsigned
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integer type, usually defined as size_t. Its maximum value (that is
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~(PCRE2_SIZE)0) is reserved as a special indicator for zero-terminated strings
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and unset offsets.
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</P>
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<P>
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Note that when using the traditional matching function, PCRE2 uses recursion to
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handle subpatterns and indefinite repetition. This means that the available
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stack space may limit the size of a subject string that can be processed by
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certain patterns. For a discussion of stack issues, see the
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<a href="pcre2stack.html"><b>pcre2stack</b></a>
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documentation.
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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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The maximum length of a lookbehind assertion is 65535 characters.
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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. There is, however, a limit to the
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depth of nesting of parenthesized subpatterns of all kinds. This is imposed in
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order to limit the amount of system stack used at compile time. The default
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limit can be specified when PCRE2 is built; the default default is 250. An
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application can change this limit by calling pcre2_set_parens_nest_limit() to
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set the limit in a compile context.
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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 code units, 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 code units for the 8-bit library and 65535 code units for the 16-bit and
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32-bit libraries.
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</P>
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<P>
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The maximum length of a string argument to a callout is the largest number a
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32-bit unsigned integer can hold.
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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, 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: 26 October 2016
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<br>
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Copyright © 1997-2016 University of Cambridge.
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<br>
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<p>
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Return to the <a href="index.html">PCRE2 index page</a>.
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</p>
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