PCRELIMITS(3) Introduction to Library Functions PCRELIMITS(3)

NAME

PCRE - Perl-compatible regular expressions

SIZE AND OTHER LIMITATIONS

There are some size limitations in PCRE but it is hoped that they
will never in practice be relevant.

The maximum length of a compiled pattern is approximately 64K data
units (bytes for the 8-bit library, 16-bit units for the 16-bit
library, and 32-bit units for the 32-bit library) if PCRE is compiled
with the default internal linkage size, which is 2 bytes for the
8-bit and 16-bit libraries, and 4 bytes for the 32-bit library. If
you want to process regular expressions that are truly enormous, you
can compile PCRE with an internal linkage size of 3 or 4 (when
building the 16-bit or 32-bit library, 3 is rounded up to 4). See the
README file in the source distribution and the pcrebuild
documentation for details. In these cases the limit is substantially
larger. However, the speed of execution is slower.

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 PCRE is
built; the default is 250.

There is a limit to the number of forward references to subsequent
subpatterns 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 characters,
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.

The maximum length of a subject string is the largest positive number
that an integer variable can hold. However, when using the
traditional matching function, PCRE 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 pcrestack documentation.

AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.

REVISION

Last updated: 05 November 2013
Copyright (c) 1997-2013 University of Cambridge.

PCRE 8.34 05 November 2013 PCRELIMITS(3)