pcre2limits


       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  64  thousand
       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.  How-
       ever, 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.

       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 groups, but there can
       be no more than 65535 capture groups, and there is 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
       default limit can be specified when PCRE2 is built; if not, the default
       is set to  250.  An  application  can  change  this  limit  by  calling
       pcre2_set_parens_nest_limit() to set the limit in a compile context.

       The  maximum length of name for a named capture group is 32 code units,
       and the maximum number of such groups is 10000.

       The maximum length of a  name  in  a  (*MARK),  (*PRUNE),  (*SKIP),  or
       (*THEN)  verb  is  255  code units for the 8-bit library and 65535 code
       units for the 16-bit and 32-bit libraries.

       The maximum length of a string argument to a  callout  is  the  largest
       number a 32-bit unsigned integer can hold.

AUTHOR

       Philip Hazel
       University Computing Service
       Cambridge, England.

REVISION
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