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PCRELIMITS(3) Library Functions Manual 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, 32-bit units for the 32-bit library, and 32-bit units for the 32-bit
library) if PCRE is compiled with the default internal linkage size of 2 bytes. 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 exe-
cution 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 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 library.
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 recur-
sion 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: 04 May 2012
Copyright (c) 1997-2012 University of Cambridge.
PCRE 8.30 24 June 2012 PCRELIMITS(3)
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