PHPでのJSONの使い方

$arr = array ('a'=>'a','b'=>'b','c'='c','d'=>'d','e'='e');
echo json_encode($arr);

class person 
{ 
  public $name; 
  public $age; 
  public $height; 
  function __construct($name,$age,$height) 
  { 
    $this->name = $name; 
    $this->age = $age; 
    $this->height = $height;   
  }  
} 
$obj = new person("zhangsan",20,100); 
$foo_json = json_encode($obj); 
echo $foo_json;

$json = '{"a":"hello","b":"world","c":"zhangsan","d":20,"e":170}'; 
var_dump(json_decode($json));

$json = '{"a":"hello","b":"world","c":"zhangsan","d":20,"e":170}';
var_dump(json_decode($json,ture));