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 64 thousand code units 24for the 8-bit and 16-bit libraries if PCRE2 is compiled with the default 25internal linkage size, which is 2 bytes for these libraries. If you want to 26process regular expressions that are truly enormous, you can compile PCRE2 with 27an internal linkage size of 3 or 4 (when building the 16-bit library, 3 is 28rounded up 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> 47All values in repeating quantifiers must be less than 65536. 48</P> 49<P> 50There are two different limits that apply to branches of lookbehind assertions. 51If every branch in such an assertion matches a fixed number of characters, 52the maximum length of any branch is 65535 characters. If any branch matches a 53variable number of characters, then the maximum matching length for every 54branch is limited. The default limit is set at compile time, defaulting to 255, 55but can be changed by the calling program. 56</P> 57<P> 58There is no limit to the number of parenthesized groups, but there can be no 59more than 65535 capture groups, and there is a limit to the depth of nesting of 60parenthesized subpatterns of all kinds. This is imposed in order to limit the 61amount of system stack used at compile time. The default limit can be specified 62when PCRE2 is built; if not, the default is set to 250. An application can 63change this limit by calling pcre2_set_parens_nest_limit() to set the limit in 64a compile context. 65</P> 66<P> 67The maximum length of name for a named capture group is 32 code units, and the 68maximum number of such groups is 10000. 69</P> 70<P> 71The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or (*THEN) verb 72is 255 code units for the 8-bit library and 65535 code units for the 16-bit and 7332-bit libraries. 74</P> 75<P> 76The maximum length of a string argument to a callout is the largest number a 7732-bit unsigned integer can hold. 78</P> 79<P> 80The maximum amount of heap memory used for matching is controlled by the heap 81limit, which can be set in a pattern or in a match context. The default is a 82very large number, effectively unlimited. 83</P> 84<br><b> 85AUTHOR 86</b><br> 87<P> 88Philip Hazel 89<br> 90Retired from University Computing Service 91<br> 92Cambridge, England. 93<br> 94</P> 95<br><b> 96REVISION 97</b><br> 98<P> 99Last updated: August 2023 100<br> 101Copyright © 1997-2023 University of Cambridge. 102<br> 103<p> 104Return to the <a href="index.html">PCRE2 index page</a>. 105</p> 106