68 lines
2.3 KiB
Groff
68 lines
2.3 KiB
Groff
|
.TH PCRELIMITS 3 "24 June 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, 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 \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 and 32-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
|