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PCRE2LIMITS(3)		   Library Functions Manual		PCRE2LIMITS(3)

       PCRE2 - Perl-compatible regular expressions (revised API)


       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  li-
       braries.	 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  in-
       ternal 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 un-
       signed integer type, usually defined as size_t. Its maximum value (that
       is ~(PCRE2_SIZE)0) is reserved as a special indicator  for  zero-termi-
       nated 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.


       Philip Hazel
       University Computing Service
       Cambridge, England.


       Last updated: 02	February 2019
       Copyright (c) 1997-2019 University of Cambridge.

PCRE2 10.33		       03 February 2019			PCRE2LIMITS(3)


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