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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>
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, 32-bit units for the 32-bit library, and 32-bit units for
25 the 32-bit library) if PCRE is compiled with the default internal linkage size
26 of 2 bytes. If you want to process regular expressions that are truly enormous,
27 you can compile PCRE with an internal linkage size of 3 or 4 (when building the
28 16-bit or 32-bit library, 3 is rounded up to 4). See the <b>README</b> file in
29 the source distribution and the
30 <a href="pcrebuild.html"><b>pcrebuild</b></a>
31 documentation for details. In these cases the limit is substantially larger.
32 However, the speed of execution is slower.
33 </P>
34 <P>
35 All values in repeating quantifiers must be less than 65536.
36 </P>
37 <P>
38 There is no limit to the number of parenthesized subpatterns, but there can be
39 no more than 65535 capturing subpatterns.
40 </P>
41 <P>
42 There is a limit to the number of forward references to subsequent subpatterns
43 of around 200,000. Repeated forward references with fixed upper limits, for
44 example, (?2){0,100} when subpattern number 2 is to the right, are included in
45 the count. There is no limit to the number of backward references.
46 </P>
47 <P>
48 The maximum length of name for a named subpattern is 32 characters, and the
49 maximum number of named subpatterns is 10000.
50 </P>
51 <P>
52 The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or (*THEN) verb
53 is 255 for the 8-bit library and 65535 for the 16-bit and 32-bit library.
54 </P>
55 <P>
56 The maximum length of a subject string is the largest positive number that an
57 integer variable can hold. However, when using the traditional matching
58 function, PCRE uses recursion to handle subpatterns and indefinite repetition.
59 This means that the available stack space may limit the size of a subject
60 string that can be processed by certain patterns. For a discussion of stack
61 issues, see the
62 <a href="pcrestack.html"><b>pcrestack</b></a>
63 documentation.
64 </P>
65 <br><b>
67 </b><br>
68 <P>
69 Philip Hazel
70 <br>
71 University Computing Service
72 <br>
73 Cambridge CB2 3QH, England.
74 <br>
75 </P>
76 <br><b>
78 </b><br>
79 <P>
80 Last updated: 04 May 2012
81 <br>
82 Copyright &copy; 1997-2012 University of Cambridge.
83 <br>
84 <p>
85 Return to the <a href="index.html">PCRE index page</a>.
86 </p>

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