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php容易被错误使用的empty函数

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在php的官方手册中写道,

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检查一个变量是否为空。
如果 var 是非空或非零的值,则 empty() 返回 FALSE。换句话说,""、0、"0"、NULL、FALSE、array()、var $var; 以及没有任何属性的对象都将被认为是空的,如果 var 为空,则返回 TRUE。?

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随后在其手册中郑重说明了,

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empty() 只检测变量,检测任何非变量的东西都将导致解析错误。换句话说,后边的语句将不会起作用: empty(addslashes($name))。 ?

empty用来检测变量是否为空,这在网站编程中经常会使用到,比如,我们在前台页面提交了用户的用户名,这时,我们需要判断是否为空,如果为空的话,让他重新提交,这时我们需要用到函数trim,即过滤掉两边的空格,然后用empty检测。

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if  (empty(trim($_GET['username'])) { …}

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但是,当我们运行这段代码的时候,却报错了。原因就在于“empty() 只检测变量”,而trim返回的确实值,不是变量。所以empty执行到这儿的时候报错了。修改方法也很简单,第一种方法:

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if  (trim($_GET['username'] == ’‘) { …}

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第二种方法,增加中间变量:

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$username = trim($_GET['username']);
if  (empty($username)) { …}
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推荐的方法是,在项目中使用验证框架来解决这个问题。

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