在PHP中键入错误:为什么根本不使用isset? [英] Weak typing in PHP: why use isset at all?

问题描述

似乎我的代码可以检查是否为空

It seems like my code works to check for null if I do

if ($tx) 

或

if (isset($tx))

为什么在写起来比较困难的时候我会做第二个?

why would I do the second one when it's harder to write?

推荐答案

我想指出的是，我在这里阅读的每个人的回复都应该添加一个警告:

I want to point out that everyone's reponse I've read here should have one caveat added:

如果测试已设置为NULL的变量，则isset()将返回FALSE" ( php.net/isset ).

这意味着在某些情况下，例如检查GET或POST参数，使用isset()足以判断是否设置了变量(因为它要么是字符串，要么是字符串将不会被设置).但是，在变量可能为NULL的情况下(当您进入对象和更复杂的应用程序时，这是很常见的情况)，isset()会让您感到茫然.

This means that in some cases, like checking for a GET or POST parameter, using isset() is enough to tell if the variable is set (because it will either be a string, or it won't be set). However, in cases where NULL is a possible value for a variable, which is fairly common when you get into objects and more complex applications, isset() leaves you high and dry.

例如(使用Suhosin-Patch 0.9.6.2(cli)在PHP 5.2.6上进行测试(内置:2008年8月17日09:05:31))

For example (tested with PHP 5.2.6 with Suhosin-Patch 0.9.6.2 (cli) (built: Aug 17 2008 09:05:31)):

<?php
$a = '';
$b = NULL;
var_dump(isset($a));
var_dump(isset($b));
var_dump(isset($c));

输出:

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

谢谢，PHP！

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