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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 65539 (sic) bytes if PCRE is
24 compiled with the default internal linkage size of 2. If you want to process
25 regular expressions that are truly enormous, you can compile PCRE with an
26 internal linkage size of 3 or 4 (see the <b>README</b> file in the source
27 distribution and the
28 <a href="pcrebuild.html"><b>pcrebuild</b></a>
29 documentation for details). In these cases the limit is substantially larger.
30 However, the speed of execution is slower.
31 </P>
32 <P>
33 All values in repeating quantifiers must be less than 65536.
34 </P>
35 <P>
36 There is no limit to the number of parenthesized subpatterns, but there can be
37 no more than 65535 capturing subpatterns.
38 </P>
39 <P>
40 There is a limit to the number of forward references to subsequent subpatterns
41 of around 200,000. Repeated forward references with fixed upper limits, for
42 example, (?2){0,100} when subpattern number 2 is to the right, are included in
43 the count. There is no limit to the number of backward references.
44 </P>
45 <P>
46 The maximum length of name for a named subpattern is 32 characters, and the
47 maximum number of named subpatterns is 10000.
48 </P>
49 <P>
50 The maximum length of a subject string is the largest positive number that an
51 integer variable can hold. However, when using the traditional matching
52 function, PCRE uses recursion to handle subpatterns and indefinite repetition.
53 This means that the available stack space may limit the size of a subject
54 string that can be processed by certain patterns. For a discussion of stack
55 issues, see the
56 <a href="pcrestack.html"><b>pcrestack</b></a>
57 documentation.
58 </P>
59 <br><b>
60 AUTHOR
61 </b><br>
62 <P>
63 Philip Hazel
64 <br>
65 University Computing Service
66 <br>
67 Cambridge CB2 3QH, England.
68 <br>
69 </P>
70 <br><b>
71 REVISION
72 </b><br>
73 <P>
74 Last updated: 30 November 2011
75 <br>
76 Copyright &copy; 1997-2011 University of Cambridge.
77 <br>
78 <p>
79 Return to the <a href="index.html">PCRE index page</a>.
80 </p>

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