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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 64 thousand 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> |
| 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 groups, but there can be no |
| more than 65535 capture groups, and there is 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 default limit can be specified |
| when PCRE2 is built; if not, the default is set to 250. An application can |
| change this limit by calling pcre2_set_parens_nest_limit() to set the limit in |
| a compile context. |
| </P> |
| <P> |
| The maximum length of name for a named capture group is 32 code units, and the |
| maximum number of such groups is 10000. |
| </P> |
| <P> |
| The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or (*THEN) verb |
| is 255 code units for the 8-bit library and 65535 code units for the 16-bit and |
| 32-bit libraries. |
| </P> |
| <P> |
| The maximum length of a string argument to a callout is the largest number a |
| 32-bit unsigned integer can hold. |
| </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: 02 February 2019 |
| <br> |
| Copyright © 1997-2019 University of Cambridge. |
| <br> |
| <p> |
| Return to the <a href="index.html">PCRE2 index page</a>. |
| </p> |