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When regexec
matches parenthetical subexpressions of
pattern, it records which parts of string they match. It
returns that information by storing the offsets into an array whose
elements are structures of type regmatch_t
. The first element of
the array (index 0
) records the part of the string that matched
the entire regular expression. Each other element of the array records
the beginning and end of the part that matched a single parenthetical
subexpression.
regmatch_t | Data Type |
This is the data type of the matcharray array that you pass to
regexec . It contains two structure fields, as follows:
|
regoff_t | Data Type |
regoff_t is an alias for another signed integer type.
The fields of regmatch_t have type regoff_t .
|
The regmatch_t
elements correspond to subexpressions
positionally; the first element (index 1
) records where the first
subexpression matched, the second element records the second
subexpression, and so on. The order of the subexpressions is the order
in which they begin.
When you call regexec
, you specify how long the matchptr
array is, with the nmatch argument. This tells regexec
how
many elements to store. If the actual regular expression has more than
nmatch subexpressions, then you won't get offset information about
the rest of them. But this doesn't alter whether the pattern matches a
particular string or not.
If you don't want regexec
to return any information about where
the subexpressions matched, you can either supply 0
for
nmatch, or use the flag REG_NOSUB
when you compile the
pattern with regcomp
.