| .TH PCRELIMITS 3 "05 November 2013" "PCRE 8.34" |
| .SH NAME |
| PCRE - Perl-compatible regular expressions |
| .SH "SIZE AND OTHER LIMITATIONS" |
| .rs |
| .sp |
| There are some size limitations in PCRE but it is hoped that they will never in |
| practice be relevant. |
| .P |
| The maximum length of a compiled pattern is approximately 64K data units (bytes |
| for the 8-bit library, 16-bit units for the 16-bit library, and 32-bit units for |
| the 32-bit library) if PCRE is compiled with the default internal linkage size, |
| which is 2 bytes for the 8-bit and 16-bit libraries, and 4 bytes for the 32-bit |
| library. If you want to process regular expressions that are truly enormous, |
| you can compile PCRE with an internal linkage size of 3 or 4 (when building the |
| 16-bit or 32-bit library, 3 is rounded up to 4). See the \fBREADME\fP file in |
| the source distribution and the |
| .\" HREF |
| \fBpcrebuild\fP |
| .\" |
| documentation for details. In these cases the limit is substantially larger. |
| However, the speed of execution is slower. |
| .P |
| All values in repeating quantifiers must be less than 65536. |
| .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 PCRE is built; the default is 250. |
| .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 |
| The maximum length of name for a named subpattern is 32 characters, and the |
| maximum number of named subpatterns is 10000. |
| .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 |
| The maximum length of a subject string is the largest positive number that an |
| integer variable can hold. However, when using the traditional matching |
| function, PCRE 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 |
| .\" HREF |
| \fBpcrestack\fP |
| .\" |
| documentation. |
| . |
| . |
| .SH AUTHOR |
| .rs |
| .sp |
| .nf |
| Philip Hazel |
| University Computing Service |
| Cambridge CB2 3QH, England. |
| .fi |
| . |
| . |
| .SH REVISION |
| .rs |
| .sp |
| .nf |
| Last updated: 05 November 2013 |
| Copyright (c) 1997-2013 University of Cambridge. |
| .fi |