我创建了一个类，无法将值加载到其数组var中

Question

The problem is that the addData function adds data to all variables but not to keywords array. As far as I can see, the keywords[1] is blank after the $keywords[]=$new_value; line. Why?? Here is my code:

class comment
{

    var $id;
    var $keywords;
    //some other vars

// This is the constructor function which assigns id property, creates keywords array.
function comment($newID) 
    {
        $this->id = $newID;
        $keywords = array();
    }

// This function is used to add data to one of the object's properties.
function addData ($prop, $new_value) 
{   // Convert the property name to lower case.
    $prop = strtolower($prop);
    if ($prop=='keywords'){
        $keywords[]=$new_value;
    }
    else 
    {
        $this->$prop = $new_value;
     }
}

}

Answer 1

You forgot the $this keyword which makes your $keywords variable just a local variable instead of a class member:

$keywords[]=$new_value;

should become

$this->keywords[]=$new_value;

You did the same thing in your comment() method.

FYI, using var to declare class member variables has been obsolete for a long time. You should be using public, protected, and private as appropriate.