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| <title>pcre2limits specification</title> |
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| <h1>pcre2limits man page</h1> |
| <p> |
| Return to the <a href="index.html">PCRE2 index page</a>. |
| </p> |
| <p> |
| This page is part of the PCRE2 HTML documentation. It was generated |
| automatically from the original man page. If there is any nonsense in it, |
| please consult the man page, in case the conversion went wrong. |
| <br> |
| <br><b> |
| SIZE AND OTHER LIMITATIONS |
| </b><br> |
| <P> |
| There are some size limitations in PCRE2 but it is hoped that they will never |
| in practice be relevant. |
| </P> |
| <P> |
| The maximum size of a compiled pattern is approximately 64K code units for the |
| 8-bit and 16-bit libraries if PCRE2 is compiled with the default internal |
| linkage size, which is 2 bytes for these libraries. If you want to process |
| regular expressions that are truly enormous, you can compile PCRE2 with an |
| internal linkage size of 3 or 4 (when building the 16-bit library, 3 is rounded |
| up to 4). See the <b>README</b> file in the source distribution and the |
| <a href="pcre2build.html"><b>pcre2build</b></a> |
| documentation for details. In these cases the limit is substantially larger. |
| However, the speed of execution is slower. In the 32-bit library, the internal |
| linkage size is always 4. |
| </P> |
| <P> |
| The maximum length of a source pattern string is essentially unlimited; it is |
| the largest number a PCRE2_SIZE variable can hold. However, the program that |
| calls <b>pcre2_compile()</b> can specify a smaller limit. |
| </P> |
| <P> |
| The maximum length (in code units) of a subject string is one less than the |
| largest number a PCRE2_SIZE variable can hold. PCRE2_SIZE is an unsigned |
| integer type, usually defined as size_t. Its maximum value (that is |
| ~(PCRE2_SIZE)0) is reserved as a special indicator for zero-terminated strings |
| and unset offsets. |
| </P> |
| <P> |
| Note that when using the traditional matching function, PCRE2 uses recursion to |
| handle subpatterns and indefinite repetition. This means that the available |
| stack space may limit the size of a subject string that can be processed by |
| certain patterns. For a discussion of stack issues, see the |
| <a href="pcre2stack.html"><b>pcre2stack</b></a> |
| documentation. |
| </P> |
| <P> |
| All values in repeating quantifiers must be less than 65536. |
| </P> |
| <P> |
| The maximum length of a lookbehind assertion is 65535 characters. |
| </P> |
| <P> |
| There is no limit to the number of parenthesized subpatterns, but there can be |
| no more than 65535 capturing subpatterns. There is, however, a limit to the |
| depth of nesting of parenthesized subpatterns of all kinds. This is imposed in |
| order to limit the amount of system stack used at compile time. The limit can |
| be specified when PCRE2 is built; the default is 250. |
| </P> |
| <P> |
| There is a limit to the number of forward references to subsequent subpatterns |
| of around 200,000. Repeated forward references with fixed upper limits, for |
| example, (?2){0,100} when subpattern number 2 is to the right, are included in |
| the count. There is no limit to the number of backward references. |
| </P> |
| <P> |
| The maximum length of name for a named subpattern is 32 code units, and the |
| maximum number of named subpatterns is 10000. |
| </P> |
| <P> |
| The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or (*THEN) verb |
| is 255 for the 8-bit library and 65535 for the 16-bit and 32-bit libraries. |
| </P> |
| <br><b> |
| AUTHOR |
| </b><br> |
| <P> |
| Philip Hazel |
| <br> |
| University Computing Service |
| <br> |
| Cambridge, England. |
| <br> |
| </P> |
| <br><b> |
| REVISION |
| </b><br> |
| <P> |
| Last updated: 05 November 2015 |
| <br> |
| Copyright © 1997-2015 University of Cambridge. |
| <br> |
| <p> |
| Return to the <a href="index.html">PCRE2 index page</a>. |
| </p> |