php如何将对象转成json格式数据

string json_encode($value[,$options=0])

<?php
   class Emp {
       public $name = "";
       public $hobbies  = "";
       public $birthdate = "";
   }
   $e = new Emp();
   $e->name = "sachin";
   $e->hobbies  = "sports";
   $e->birthdate = date(&#39;m/d/Y h:i:s a&#39;, "8/5/1974 12:20:03 p");
   $e->birthdate = date(&#39;m/d/Y h:i:s a&#39;, strtotime("8/5/1974 12:20:03"));

   echo json_encode($e);
?>

{"name":"sachin","hobbies":"sports","birthdate":"08\/05\/1974 12:20:03 pm"}