_CP_occurs is equivalent to the result = occurs(string, expression) BASIC function.
int _CP_occurs(CPSTR** result, CPSTR* string, int expression)
This function returns -1 if an error occurs. The error code is contained in _CP_errno.
/* Prints "a". */
CPSTR * s = _CP_mkstr("a\376a");
_CP_occurs(&s,s,2);
_CP_print(s);