How does it work?

For each parameter in your functions prototype there will be a local C variable of the same name and an appropriate type.

For string parameters the actual string length is storen in an additional int variable that is named like the parameter but with an additional '_len' suffix.

The mapping from PHP to C variable types is as follows:

PHP type	C type
bool	zend_bool
int	long
float	double
string	char *
array	zval *
object	zval *
resource	zval *
callback	zval *
mixed	zval *