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 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.   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.

       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.

       The  maximum amount of heap memory used for matching is controlled by the heap limit, which can be set in
       a pattern or in a match context. The default is a very large number, effectively unlimited.

AUTHOR

       Philip Hazel
       Retired from University Computing Service
       Cambridge, England.

REVISION

       Last updated: 26 July 2022
       Copyright (c) 1997-2022 University of Cambridge.

PCRE2 10.41                                       26 July 2022                                    PCRE2LIMITS(3)