+Return to the PCRE2 index page. +
+
+This page is part of the PCRE2 HTML documentation. It was generated
+automatically from the original man page. If there is any nonsense in it,
+please consult the man page, in case the conversion went wrong.
+
+
+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. +
++The maximum length of a lookbehind assertion is 65535 characters. +
++There is no limit to the number of parenthesized subpatterns, but there can be +no more than 65535 capturing subpatterns. There is, however, 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 subpattern is 32 code units, and the +maximum number of named subpatterns 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. +
+
+Philip Hazel
+
+University Computing Service
+
+Cambridge, England.
+
+
+Last updated: 30 March 2017
+
+Copyright © 1997-2017 University of Cambridge.
+
+
+Return to the PCRE2 index page. +