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 64K code  units
14       for  the  8-bit  and  16-bit  libraries  if  PCRE2 is compiled with the
15       default internal linkage size, which is 2 bytes for these libraries. If
16       you  want  to  process regular expressions that are truly enormous, you
17       can compile PCRE2 with an internal linkage size of 3 or 4 (when  build‐
18       ing  the  16-bit library, 3 is rounded up to 4). See the README file in
19       the source distribution and the pcre2build documentation  for  details.
20       In  these  cases the limit is substantially larger.  However, the speed
21       of execution is slower. In the 32-bit  library,  the  internal  linkage
22       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
30       unsigned  integer  type,  usually  defined as size_t. Its maximum value
31       (that is ~(PCRE2_SIZE)0) is reserved as a special indicator  for  zero-
32       terminated strings and unset offsets.
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34       Note  that  when  using  the  traditional matching function, PCRE2 uses
35       recursion to handle subpatterns and indefinite repetition.  This  means
36       that  the  available stack space may limit the size of a subject string
37       that can be processed by certain patterns. For a  discussion  of  stack
38       issues, see the pcre2stack documentation.
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40       All values in repeating quantifiers must be less than 65536.
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42       The maximum length of a lookbehind assertion is 65535 characters.
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44       There is no limit to the number of parenthesized subpatterns, but there
45       can be no more than 65535 capturing subpatterns. There is,  however,  a
46       limit  to  the  depth  of  nesting  of parenthesized subpatterns of all
47       kinds. This is imposed in order to limit the  amount  of  system  stack
48       used  at compile time. The default limit can be specified when PCRE2 is
49       built; the default default is 250. An application can change this limit
50       by  calling pcre2_set_parens_nest_limit() to set the limit in a compile
51       context.
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53       The maximum length of name for a named subpattern is 32 code units, and
54       the maximum number of named subpatterns is 10000.
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56       The  maximum  length  of  a  name  in  a (*MARK), (*PRUNE), (*SKIP), or
57       (*THEN) verb is 255 code units for the 8-bit  library  and  65535  code
58       units for the 16-bit and 32-bit libraries.
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60       The  maximum  length  of  a string argument to a callout is the largest
61       number a 32-bit unsigned integer can hold.
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AUTHOR

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65       Philip Hazel
66       University Computing Service
67       Cambridge, England.
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REVISION

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71       Last updated: 26 October 2016
72       Copyright (c) 1997-2016 University of Cambridge.
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76PCRE2 10.23                     26 October 2016                 PCRE2LIMITS(3)