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> 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 © 1997-2012 University of Cambridge. 82<br> 83<p> 84Return to the <a href="index.html">PCRE index page</a>. 85</p> 86