PCRE2LIMITS(3)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 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 build‐
ing 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 (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.
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 sub‐
patterns 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: 25 November 2014
Copyright (c) 1997-2014 University of Cambridge.
PCRE2 10.00 25 November 2014 PCRE2LIMITS(3)
