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   pcreapi    ( 3 )

Perl-совместимые регулярные выражения (Perl-compatible regular expressions)
  Name  |  Pcre native api basic functions  |  Pcre native api string extraction functions  |  Pcre native api auxiliary functions  |  Pcre native api indirected functions  |  Pcre 8-bit, 16-bit, and 32-bit libraries  |  Pcre api overview  |  Newlines  |  Multithreading  |  Saving precompiled patterns for later use  |  Checking build-time options  |  Compiling a pattern  |  Compilation error codes  |  Studying a pattern  |  Locale support  |  Information about a pattern  |  Reference counts  |  Matching a pattern: the traditional function  |  Extracting captured substrings by number  |  Extracting captured substrings by name  |  Duplicate subpattern names  |  Finding all possible matches  |    Obtaining an estimate of stack usage    |  Matching a pattern: the alternative function  |  See also  |

OBTAINING AN ESTIMATE OF STACK USAGE

Matching certain patterns using pcre_exec() can use a lot of process stack, which in certain environments can be rather limited in size. Some users find it helpful to have an estimate of the amount of stack that is used by pcre_exec(), to help them set recursion limits, as described in the pcrestack documentation. The estimate that is output by pcretest when called with the -m and -C options is obtained by calling pcre_exec with the values NULL, NULL, NULL, -999, and -999 for its first five arguments.

Normally, if its first argument is NULL, pcre_exec() immediately returns the negative error code PCRE_ERROR_NULL, but with this special combination of arguments, it returns instead a negative number whose absolute value is the approximate stack frame size in bytes. (A negative number is used so that it is clear that no match has happened.) The value is approximate because in some cases, recursive calls to pcre_exec() occur when there are one or two additional variables on the stack.

If PCRE has been compiled to use the heap instead of the stack for recursion, the value returned is the size of each block that is obtained from the heap.