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

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