75 lines
2.7 KiB
Groff
75 lines
2.7 KiB
Groff
.TH PCRE2LIMITS 3 "25 November 2014" "PCRE2 10.00"
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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 64K code units for the
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8-bit and 16-bit libraries if PCRE2 is compiled with the default internal
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linkage size, which is 2 bytes for these libraries. If you want to process
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regular expressions that are truly enormous, you can compile PCRE2 with an
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internal linkage size of 3 or 4 (when building the 16-bit library, 3 is rounded
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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 (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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Note that when using the traditional matching function, PCRE2 uses recursion to
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handle subpatterns and indefinite repetition. This means that the available
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stack space may limit the size of a subject string that can be processed by
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certain patterns. For a discussion of stack issues, see the
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.\" HREF
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\fBpcre2stack\fP
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.\"
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documentation.
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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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There is no limit to the number of parenthesized subpatterns, but there can be
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no more than 65535 capturing subpatterns. There is, however, a limit to the
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depth of nesting of parenthesized subpatterns of all kinds. This is imposed in
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order to limit the amount of system stack used at compile time. The limit can
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be specified when PCRE2 is built; the default is 250.
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.P
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There is a limit to the number of forward references to subsequent subpatterns
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of around 200,000. Repeated forward references with fixed upper limits, for
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example, (?2){0,100} when subpattern number 2 is to the right, are included in
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the count. There is no limit to the number of backward references.
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.P
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The maximum length of name for a named subpattern is 32 code units, and the
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maximum number of named subpatterns 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 for the 8-bit library and 65535 for the 16-bit and 32-bit libraries.
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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: 25 November 2014
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Copyright (c) 1997-2014 University of Cambridge.
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.fi
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