PCRELIMITS(3)              Library Functions Manual              PCRELIMITS(3)

       PCRE - Perl-compatible regular expressions


       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 li-
       brary, 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 sub-
       patterns of around 200,000. Repeated forward references with fixed  up-
       per 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 indef-
       inite  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.


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


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

PCRE 8.34                      05 November 2013                  PCRELIMITS(3)
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