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.TH PCRELIMITS 3 "04 May 2012" "PCRE 8.30"
.SH NAME
PCRE - Perl-compatible regular expressions
.SH "SIZE AND OTHER LIMITATIONS"
.rs
.sp
There are some size limitations in PCRE but it is hoped that they will never in
practice be relevant.
.P
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) 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 library, 3 is rounded
up to 4). See the \fBREADME\fP file in the source distribution and the
.\" HREF
\fBpcrebuild\fP
.\"
documentation for details. In these cases the limit is substantially larger.
However, the speed of execution is slower.
.P
All values in repeating quantifiers must be less than 65536.
.P
There is no limit to the number of parenthesized subpatterns, but there can be
no more than 65535 capturing subpatterns.
.P
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.
.P
The maximum length of name for a named subpattern is 32 characters, and the
maximum number of named subpatterns is 10000.
.P
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 library.
.P
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
.\" HREF
\fBpcrestack\fP
.\"
documentation.
.
.
.SH AUTHOR
.rs
.sp
.nf
Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.
.fi
.
.
.SH REVISION
.rs
.sp
.nf
Last updated: 04 May 2012
Copyright (c) 1997-2012 University of Cambridge.
.fi
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