json_encode和json_decode

<?php 
$json = '{"a":1,"b":2,"c":3,"d":4,"e":5}'; 
var_dump(json_decode($json)); 
var_dump(json_decode($json, true)); 
?> 

object(stdClass)#1 (5) { 
["a"] => int(1) 
["b"] => int(2) 
["c"] => int(3) 
["d"] => int(4) 
["e"] => int(5) 
} 

array(5) { 
["a"] => int(1) 
["b"] => int(2) 
["c"] => int(3) 
["d"] => int(4) 
["e"] => int(5) 
} 

可以看出 json_decode($data,true)输出的一个关联数组,由此可知json_decode($data）输出的是对象,而json_decode("$arr",true)是把它强制生成PHP关联数组.