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3<title>pcrelimits specification</title>
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6<h1>pcrelimits man page</h1>
7<p>
8Return to the <a href="index.html">PCRE index page</a>.
9</p>
10<p>
11This page is part of the PCRE HTML documentation. It was generated automatically
12from the original man page. If there is any nonsense in it, please consult the
13man page, in case the conversion went wrong.
14<br>
15<br><b>
16SIZE AND OTHER LIMITATIONS
17</b><br>
18<P>
19There are some size limitations in PCRE but it is hoped that they will never in
20practice be relevant.
21</P>
22<P>
23The maximum length of a compiled pattern is approximately 64K data units (bytes
24for the 8-bit library, 16-bit units for the 16-bit library) if PCRE is compiled
25with the default internal linkage size of 2 bytes. If you want to process
26regular expressions that are truly enormous, you can compile PCRE with an
27internal linkage size of 3 or 4 (when building the 16-bit library, 3 is rounded
28up to 4). See the <b>README</b> file in the source distribution and the
29<a href="pcrebuild.html"><b>pcrebuild</b></a>
30documentation for details. In these cases the limit is substantially larger.
31However, the speed of execution is slower.
32</P>
33<P>
34All values in repeating quantifiers must be less than 65536.
35</P>
36<P>
37There is no limit to the number of parenthesized subpatterns, but there can be
38no more than 65535 capturing subpatterns.
39</P>
40<P>
41There is a limit to the number of forward references to subsequent subpatterns
42of around 200,000. Repeated forward references with fixed upper limits, for
43example, (?2){0,100} when subpattern number 2 is to the right, are included in
44the count. There is no limit to the number of backward references.
45</P>
46<P>
47The maximum length of name for a named subpattern is 32 characters, and the
48maximum number of named subpatterns is 10000.
49</P>
50<P>
51The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or (*THEN) verb
52is 255 for the 8-bit library and 65535 for the 16-bit library.
53</P>
54<P>
55The maximum length of a subject string is the largest positive number that an
56integer variable can hold. However, when using the traditional matching
57function, PCRE uses recursion to handle subpatterns and indefinite repetition.
58This means that the available stack space may limit the size of a subject
59string that can be processed by certain patterns. For a discussion of stack
60issues, see the
61<a href="pcrestack.html"><b>pcrestack</b></a>
62documentation.
63</P>
64<br><b>
65AUTHOR
66</b><br>
67<P>
68Philip Hazel
69<br>
70University Computing Service
71<br>
72Cambridge CB2 3QH, England.
73<br>
74</P>
75<br><b>
76REVISION
77</b><br>
78<P>
79Last updated: 04 May 2012
80<br>
81Copyright &copy; 1997-2012 University of Cambridge.
82<br>
83<p>
84Return to the <a href="index.html">PCRE index page</a>.
85</p>
86