1<html> 2<head> 3<title>pcre2limits specification</title> 4</head> 5<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB"> 6<h1>pcre2limits man page</h1> 7<p> 8Return to the <a href="index.html">PCRE2 index page</a>. 9</p> 10<p> 11This page is part of the PCRE2 HTML documentation. It was generated 12automatically from the original man page. If there is any nonsense in it, 13please consult the man 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 PCRE2 but it is hoped that they will never 20in practice be relevant. 21</P> 22<P> 23The maximum size of a compiled pattern is approximately 64K code units for the 248-bit and 16-bit libraries if PCRE2 is compiled with the default internal 25linkage size, which is 2 bytes for these libraries. If you want to process 26regular expressions that are truly enormous, you can compile PCRE2 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="pcre2build.html"><b>pcre2build</b></a> 30documentation for details. In these cases the limit is substantially larger. 31However, the speed of execution is slower. In the 32-bit library, the internal 32linkage size is always 4. 33</P> 34<P> 35The maximum length of a source pattern string is essentially unlimited; it is 36the largest number a PCRE2_SIZE variable can hold. However, the program that 37calls <b>pcre2_compile()</b> can specify a smaller limit. 38</P> 39<P> 40The maximum length (in code units) of a subject string is one less than the 41largest number a PCRE2_SIZE variable can hold. PCRE2_SIZE is an unsigned 42integer type, usually defined as size_t. Its maximum value (that is 43~(PCRE2_SIZE)0) is reserved as a special indicator for zero-terminated strings 44and unset offsets. 45</P> 46<P> 47Note that when using the traditional matching function, PCRE2 uses recursion to 48handle subpatterns and indefinite repetition. This means that the available 49stack space may limit the size of a subject string that can be processed by 50certain patterns. For a discussion of stack issues, see the 51<a href="pcre2stack.html"><b>pcre2stack</b></a> 52documentation. 53</P> 54<P> 55All values in repeating quantifiers must be less than 65536. 56</P> 57<P> 58The maximum length of a lookbehind assertion is 65535 characters. 59</P> 60<P> 61There is no limit to the number of parenthesized subpatterns, but there can be 62no more than 65535 capturing subpatterns. There is, however, a limit to the 63depth of nesting of parenthesized subpatterns of all kinds. This is imposed in 64order to limit the amount of system stack used at compile time. The limit can 65be specified when PCRE2 is built; the default is 250. 66</P> 67<P> 68There is a limit to the number of forward references to subsequent subpatterns 69of around 200,000. Repeated forward references with fixed upper limits, for 70example, (?2){0,100} when subpattern number 2 is to the right, are included in 71the count. There is no limit to the number of backward references. 72</P> 73<P> 74The maximum length of name for a named subpattern is 32 code units, and the 75maximum number of named subpatterns is 10000. 76</P> 77<P> 78The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or (*THEN) verb 79is 255 for the 8-bit library and 65535 for the 16-bit and 32-bit libraries. 80</P> 81<br><b> 82AUTHOR 83</b><br> 84<P> 85Philip Hazel 86<br> 87University Computing Service 88<br> 89Cambridge, England. 90<br> 91</P> 92<br><b> 93REVISION 94</b><br> 95<P> 96Last updated: 05 November 2015 97<br> 98Copyright © 1997-2015 University of Cambridge. 99<br> 100<p> 101Return to the <a href="index.html">PCRE2 index page</a>. 102</p> 103