77 lines
2.8 KiB
Groff
77 lines
2.8 KiB
Groff
.TH PCRE2LIMITS 3 "03 November 2015" "PCRE2 10.21"
|
|
.SH NAME
|
|
PCRE2 - Perl-compatible regular expressions (revised API)
|
|
.SH "SIZE AND OTHER LIMITATIONS"
|
|
.rs
|
|
.sp
|
|
There are some size limitations in PCRE2 but it is hoped that they will never
|
|
in practice be relevant.
|
|
.P
|
|
The maximum size of a compiled pattern is approximately 64K 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 \fBREADME\fP file in the source distribution and the
|
|
.\" HREF
|
|
\fBpcre2build\fP
|
|
.\"
|
|
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.
|
|
.P
|
|
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.
|
|
.P
|
|
Note that when using the traditional matching function, PCRE2 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
|
|
\fBpcre2stack\fP
|
|
.\"
|
|
documentation.
|
|
.P
|
|
All values in repeating quantifiers must be less than 65536.
|
|
.P
|
|
The maximum length of a lookbehind assertion is 65535 characters.
|
|
.P
|
|
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 PCRE2 is built; the default is 250.
|
|
.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 code units, 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 libraries.
|
|
.
|
|
.
|
|
.SH AUTHOR
|
|
.rs
|
|
.sp
|
|
.nf
|
|
Philip Hazel
|
|
University Computing Service
|
|
Cambridge, England.
|
|
.fi
|
|
.
|
|
.
|
|
.SH REVISION
|
|
.rs
|
|
.sp
|
|
.nf
|
|
Last updated: 03 November 2015
|
|
Copyright (c) 1997-2015 University of Cambridge.
|
|
.fi
|