PCRE2LIMITS(3) Introduction to Library Functions 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: 16 August 2023
Copyright (c) 1997-2023 University of Cambridge.

PCRE2 10.45 16 August 2023 PCRE2LIMITS(3)