# pcre2limits

## NAME



           PCRE2 - Perl-compatible regular expressions (revised API)
    


## SIZE AND OTHER LIMITATIONS



    
           There are some size limitations in PCRE2 but it is hoped that they
           will never in practice be relevant.
    
           The maximum size of a compiled pattern is approximately 64
           thousand 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 **README** file in the source distribution
           and the **pcre2build** 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.
    
           The maximum length of a source pattern string is essentially
           unlimited; it is the largest number a PCRE2_SIZE variable can
           hold. However, the program that calls **pcre2_compile()** can specify
           a smaller limit.
    
           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.
    
           All values in repeating quantifiers must be less than 65536.
    
           There are two different limits that apply to branches of
           lookbehind assertions.  If every branch in such an assertion
           matches a fixed number of characters, the maximum length of any
           branch is 65535 characters. If any branch matches a variable
           number of characters, then the maximum matching length for every
           branch is limited. The default limit is set at compile time,
           defaulting to 255, but can be changed by the calling program.
    
           There is no limit to the number of parenthesized groups, but there
           can be no more than 65535 capture groups, and there is 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 default limit can be specified when PCRE2 is
           built; if not, the default is set to 250. An application can
           change this limit by calling pcre2_set_parens_nest_limit() to set
           the limit in a compile context.
    
           The maximum length of name for a named capture group is 32 code
           units, and the maximum number of such groups is 10000.
    
           The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or
           (*THEN) verb is 255 code units for the 8-bit library and 65535
           code units for the 16-bit and 32-bit libraries.
    
           The maximum length of a string argument to a callout is the
           largest number a 32-bit unsigned integer can hold.
    
           The maximum amount of heap memory used for matching is controlled
           by the heap limit, which can be set in a pattern or in a match
           context. The default is a very large number, effectively
           unlimited.
    


## REVISION



    
           Last updated: 16 August 2023
           Copyright (c) 1997-2023 University of Cambridge.
    


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