zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "ss", &r1, &n, &r2, &m)
What's "ss" for here?
"ss" is type_spec string
check this rosource out http://docstore.mik.ua/orelly/weblinux2/php/ch14_07.htm
It is type_spec. Check here
The type specifier in your case is "ss". The specifier s is for a string. Since you are requesting two string parameters you need to supply two s as ss:
zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "ss", &field1 &field1_length,
&field2, &field2_length)
that php function expects 2 strings parameteres, that's why 2 s's. every string in php is defined by a pointer and a length. that's why you have
&r1, &n, -> 1st string &r2, &m -> 2nd string.