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PHP中isset(变量)和直接判断变量的区别

Jun 23, 2016 pm 01:29 PM

在变量为空字符串和布尔值false以及数值0时,isset全部返回true,直接判断全部返回false:

$empty='';echo (isset($empty)?'1':0);//1echo '<br/>';echo ($empty?'1':0);//0
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$empty=false;echo (isset($empty)?'1':0);//1echo '<br/>';echo ($empty?'1':0);//0
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$empty=0;echo (isset($empty)?'1':0);//1echo '<br/>';echo ($empty?'1':0);//0
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只有在变量为null时,它们才是没有区别的:

$empty=null;echo (isset($empty)?'1':0);//0echo '<br/>';echo ($empty?'1':0);//0
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虽然isset在判断变量没什么作用,但是在判断数组有无一个变量却很好用:

$arr=array('1'=>1,'3'=>3);$temp=null;//PS:php中数组不同于map,如果没有key而你去取值会引发错误而不是返回null,所以要有对应的判断,先判断再取值if (isset($arr['2'])) {//效果等同于array_key_exists('2', $arr),但相对代码短一点    $temp=$arr['2'];}echo $temp;
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还有对isset不了解的可以去官网看一下就明白了:
http://php.net/manual/zh/function.isset.php

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