73 lines
2.7 KiB
Groff
73 lines
2.7 KiB
Groff
.TH PCRE2LIMITS 3 "03 February 2019" "PCRE2 10.33"
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.SH NAME
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PCRE2 - Perl-compatible regular expressions (revised API)
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.SH "SIZE AND OTHER LIMITATIONS"
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.rs
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.sp
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There are some size limitations in PCRE2 but it is hoped that they will never
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in practice be relevant.
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.P
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The maximum size of a compiled pattern is approximately 64 thousand code units
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for the 8-bit and 16-bit libraries if PCRE2 is compiled with the default
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internal linkage size, which is 2 bytes for these libraries. If you want to
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process regular expressions that are truly enormous, you can compile PCRE2 with
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an internal linkage size of 3 or 4 (when building the 16-bit library, 3 is
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rounded up to 4). See the \fBREADME\fP file in the source distribution and the
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.\" HREF
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\fBpcre2build\fP
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.\"
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documentation for details. In these cases the limit is substantially larger.
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However, the speed of execution is slower. In the 32-bit library, the internal
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linkage size is always 4.
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.P
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The maximum length of a source pattern string is essentially unlimited; it is
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the largest number a PCRE2_SIZE variable can hold. However, the program that
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calls \fBpcre2_compile()\fP can specify a smaller limit.
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.P
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The maximum length (in code units) of a subject string is one less than the
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largest number a PCRE2_SIZE variable can hold. PCRE2_SIZE is an unsigned
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integer type, usually defined as size_t. Its maximum value (that is
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~(PCRE2_SIZE)0) is reserved as a special indicator for zero-terminated strings
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and unset offsets.
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.P
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All values in repeating quantifiers must be less than 65536.
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.P
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The maximum length of a lookbehind assertion is 65535 characters.
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.P
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There is no limit to the number of parenthesized groups, but there can be no
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more than 65535 capture groups, and there is a limit to the depth of nesting of
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parenthesized subpatterns of all kinds. This is imposed in order to limit the
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amount of system stack used at compile time. The default limit can be specified
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when PCRE2 is built; if not, the default is set to 250. An application can
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change this limit by calling pcre2_set_parens_nest_limit() to set the limit in
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a compile context.
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.P
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The maximum length of name for a named capture group is 32 code units, and the
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maximum number of such groups is 10000.
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.P
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The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or (*THEN) verb
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is 255 code units for the 8-bit library and 65535 code units for the 16-bit and
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32-bit libraries.
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.P
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The maximum length of a string argument to a callout is the largest number a
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32-bit unsigned integer can hold.
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.
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.
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.SH AUTHOR
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.rs
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.sp
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.nf
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Philip Hazel
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University Computing Service
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Cambridge, England.
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.fi
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.
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.
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.SH REVISION
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.rs
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.sp
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.nf
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Last updated: 02 February 2019
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Copyright (c) 1997-2019 University of Cambridge.
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.fi
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