php——字符串的""和null,empty的关系

public function test(){
    $test = "";
    if($test==null){
        echo "test==null <hr>";
    }else{
        echo "test!=null <hr>";
    }
    if(empty($test)){
        echo "test is empty <hr>";
    }else{
        echo "test is not empty <hr>";
    }
    $test1 = null;
    if(empty($test1)){
        echo "null is empty <hr>";
    }else{
        echo "null is not empty <hr>";
    }
    //null == "" == empty
}

结果:

test==null
test is empty
null is empty

注:""表示字符串类型的空