PCRELIMITS(3)          FreeBSD Library Functions 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, 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 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, 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.

       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 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.

       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: 05 November 2013
       Copyright (c) 1997-2013 University of Cambridge.

PCRE 8.34                      05 November 2013                  PCRELIMITS(3)