Convert stdClass object to array in PHP

I fetch post_id from postmeta as:

$post_id = $wpdb->get_results("SELECT post_id FROM $wpdb->postmeta WHERE (meta_key = 'mfn-post-link1' AND meta_value = '". $from ."')");

when i try print_r($post_id); I have array like this:

Array
(
    [0] => stdClass Object
        (
            [post_id] => 140
        )

    [1] => stdClass Object
        (
            [post_id] => 141
        )

    [2] => stdClass Object
        (
            [post_id] => 142
        )

)

and i dont know how to traverse it, and how could I get array like this

Array
(
    [0]  => 140


    [1] => 141


    [2] => 142

)

Any idea how can I do this?

The easiest way is to JSON-encode your object and then decode it back to an array:

$array = json_decode(json_encode($object), true);

Or if you prefer, you can traverse the object manually, too:

foreach ($object as $value) 
    $array[] = $value->post_id;

Very simple, first turn your object into a json object, this will return a string of your object into a JSON representative.

Take that result and decode with an extra parameter of true, where it will convert to associative array

$array = json_decode(json_encode($oObject),true);

Try this:

$new_array = objectToArray($yourObject);

function objectToArray($d) 
{
    if (is_object($d)) {
        // Gets the properties of the given object
        // with get_object_vars function
        $d = get_object_vars($d);
    }

    if (is_array($d)) {
        /*
        * Return array converted to object
        * Using __FUNCTION__ (Magic constant)
        * for recursive call
        */
        return array_map(__FUNCTION__, $d);
    } else {
        // Return array
        return $d;
    }
}

You can convert an std object to array like this:

$objectToArray = (array)$object;