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
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.
There are two different limits that apply to branches of lookbehind
assertions. 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: August 2023
Copyright (c) 1997-2023 University of Cambridge.
PCRE2 10.43 1 August 2023 pcre2limits(3)
pcre2 10.43 - Generated Sat Mar 2 13:14:35 CST 2024