Simple Demonstration object to Array

object2array.php

<?php
$post_id = array((object) (array(
   'index_id' => 'Mahfuz',
)), (object) (array(
   'index_id' => 'mstmhaque@gmail.com',
)), (object) (array(
   'index_id' => 142,
)));

foreach ($post_id as $key => $value) {
    $result[] = $value->index_id;
}

print_r($result);