To free any allocated fields of a pattern buffer, use the POSIX
void regfree (regex_t *preg)
preg is the pattern buffer whose allocated fields you want freed;
this works because since the type
regex_t—the type for
POSIX pattern buffers—is equivalent to the type
regfree also sets preg’s
allocated field to zero.
After a buffer has been freed, it must have a regular expression
compiled in it before passing it to a matching or searching function.