为什么当class_name为null时mysql_fetch_object失败，即使这是默认值？

Question

I'm trying to write a simple database wrapper class. I've written a method like so:

public function get_objects($sql, $class_name = null) {
    $result = mysql_query( $sql, $this->connection );
    $objs = array();
    if( $result ) {
        while ($obj = mysql_fetch_object($result, $class_name)) {
            $objs[] = $obj;
        }
        mysql_free_result($result);
    }
    return $objs;
}

If I don't specify $class_name when calling this method the call to mysql_fetch_object fails with the following error:

PHP Fatal error:  Class '' not found in ...

The problem is I don't want it to use a class_name. I just want it to perform the default behavior as if I hadn't specified a class_name.

Why is this failing?

Answer 1

The default isn't null. The default is stdClass (from the docs):

The name of the class to instantiate, set the properties of and return. If not specified, a stdClass object is returned.

If you want to keep the same default, you'll need to have this as your method signature:

 public function get_objects($sql, $class_name = "stdClass") {
     // continue as normal.