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PCRE2LIMITS(3)		   Library Functions Manual		PCRE2LIMITS(3)

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  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.

       There are two different limits that apply to branches of	lookbehind as-
       sertions.   If every branch in such an assertion	matches	a fixed	number
       of characters, the maximum length of any	branch is 65535	characters. If
       any branch matches a variable number of characters,  then  the  maximum
       matching	 length	 for every branch is limited. The default limit	is set
       at compile time,	defaulting to 255, but can be changed by  the  calling
       program.

       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: 16	August 2023
       Copyright (c) 1997-2023 University of Cambridge.

PCRE2 10.45			16 August 2023			PCRE2LIMITS(3)

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