PCRELIMITS(3)             OpenBSD Programmer's Manual            PCRELIMITS(3)



NAME
       PCRE - Perl-compatible regular expressions

SIZE AND OTHER LIMITATIONS

       There are some size limitations in PCRE but it is hoped that they will
       never in practice be relevant.

       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) if PCRE is compiled with the default internal linkage size of
       2 bytes. 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 library, 3 is rounded up to 4). See the
       README file in the source distribution and the pcrebuild documentation
       for details. In these cases the limit is substantially larger.
       However, the speed of execution is slower.

       All values in repeating quantifiers must be less than 65536.

       There is no limit to the number of parenthesized subpatterns, but there
       can be no more than 65535 capturing subpatterns.

       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.

       The maximum length of name for a named subpattern is 32 characters, and
       the maximum number of named subpatterns is 10000.

       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 pcrestack
       documentation.

AUTHOR

       Philip Hazel
       University Computing Service
       Cambridge CB2 3QH, England.

REVISION

       Last updated: 08 January 2012
       Copyright (c) 1997-2012 University of Cambridge.



                                                                 PCRELIMITS(3)
