1PCRE2LIMITS(3)             Library Functions Manual             PCRE2LIMITS(3)
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NAME

6       PCRE2 - Perl-compatible regular expressions (revised API)
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SIZE AND OTHER LIMITATIONS

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10       There are some size limitations in PCRE2 but it is hoped that they will
11       never in practice be relevant.
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13       The maximum size of a compiled pattern  is  approximately  64  thousand
14       code units for the 8-bit and 16-bit libraries if PCRE2 is compiled with
15       the default internal linkage size, which  is  2  bytes  for  these  li‐
16       braries.  If  you  want  to  process regular expressions that are truly
17       enormous, you can compile PCRE2 with an internal linkage size of 3 or 4
18       (when  building  the  16-bit  library,  3  is rounded up to 4). See the
19       README file in the source distribution and the pcre2build documentation
20       for  details.  In  these cases the limit is substantially larger.  How‐
21       ever, the speed of execution is slower. In the 32-bit library, the  in‐
22       ternal linkage size is always 4.
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24       The maximum length of a source pattern string is essentially unlimited;
25       it is the largest number a PCRE2_SIZE variable can hold.  However,  the
26       program that calls pcre2_compile() can specify a smaller limit.
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28       The maximum length (in code units) of a subject string is one less than
29       the largest number a PCRE2_SIZE variable can hold. PCRE2_SIZE is an un‐
30       signed integer type, usually defined as size_t. Its maximum value (that
31       is ~(PCRE2_SIZE)0) is reserved as a special indicator  for  zero-termi‐
32       nated strings and unset offsets.
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34       All values in repeating quantifiers must be less than 65536.
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36       The maximum length of a lookbehind assertion is 65535 characters.
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38       There  is no limit to the number of parenthesized groups, but there can
39       be no more than 65535 capture groups, and there is a limit to the depth
40       of  nesting  of parenthesized subpatterns of all kinds. This is imposed
41       in order to limit the amount of system stack used at compile time.  The
42       default limit can be specified when PCRE2 is built; if not, the default
43       is set to  250.  An  application  can  change  this  limit  by  calling
44       pcre2_set_parens_nest_limit() to set the limit in a compile context.
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46       The  maximum length of name for a named capture group is 32 code units,
47       and the maximum number of such groups is 10000.
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49       The maximum length of a  name  in  a  (*MARK),  (*PRUNE),  (*SKIP),  or
50       (*THEN)  verb  is  255  code units for the 8-bit library and 65535 code
51       units for the 16-bit and 32-bit libraries.
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53       The maximum length of a string argument to a  callout  is  the  largest
54       number a 32-bit unsigned integer can hold.
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56       The  maximum  amount  of heap memory used for matching is controlled by
57       the heap limit, which can be set in a pattern or in  a  match  context.
58       The default is a very large number, effectively unlimited.
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AUTHOR

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62       Philip Hazel
63       Retired from University Computing Service
64       Cambridge, England.
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REVISION

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68       Last updated: 26 July 2022
69       Copyright (c) 1997-2022 University of Cambridge.
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73PCRE2 10.41                      26 July 2022                   PCRE2LIMITS(3)
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