php 5.2 版本isset()方法小坑

PHP 5.2.17p1 (cli) (built: May 28 2015 16:15:30)
Copyright (c) 1997-2010 The PHP Group
Zend Engine v2.2.0, Copyright (c) 1998-2010 Zend Technologies

<?php

$s = json_encode(array("cost" => "199000000000&444838oo88888ooooo38338384&132132121321&"));
var_dump(isset($s['ecode_cost_detail']));

$s = array(1);
var_dump(isset($s['ecode_cost_detail']));

$s = "";
var_dump(isset($s['ecode_cost_detail']));

$s = null;
var_dump(isset($s['ecode_cost_detail']));

$s = "mmmmm";
var_dump(isset($s['ecode_cost_detail']));

返回结果

bool(true)
bool(false)
bool(false)
bool(false)
bool(true)

对于5.6版本

返回结果

bool(false)
bool(false)
bool(false)
bool(false)
bool(false)