如何获得函数本身有多少个参数

怎么获得函数本身有多少个参数？

function hello($param1,$param2,...){
	echo 'function name is:'. __FUNCTION__; // get function itself name
	// how to get how many parameters in these function ,
	echo '
has ? parameters';
}
hello();

function hello(){
    echo 'function name is:'. __FUNCTION__; // get function itself name
    // how to get how many parameters in these function ,
    echo '
has '.func_num_args().' parameters
';
    $params = func_get_args();
    foreach($params as $param){
        echo $param.'
';
    }
}
hello(1,2,3);