NAME

       PCRE2 - Perl-compatible regular expressions (revised API)

SIZE AND OTHER LIMITATIONS

       There are some size limitations in PCRE2 but it is hoped that they will never in practice be relevant.

       The maximum size of a compiled pattern is approximately 64K 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 README  file  in
       the  source  distribution  and  the  pcre2build  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.

       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  pcre2_compile()  can  specify  a  smaller
       limit.

       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.

       Note that when using the traditional matching function, PCRE2 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  pcre2stack
       documentation.

       All values in repeating quantifiers must be less than 65536.

       The maximum length of a lookbehind assertion is 65535 characters.

       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 PCRE2 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 code units,  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.

AUTHOR

       Philip Hazel
       University Computing Service
       Cambridge, England.

REVISION

       Last updated: 05 November 2015
       Copyright (c) 1997-2015 University of Cambridge.

PCRE2 10.21                                     05 November 2015                                  PCRE2LIMITS(3)