为什么 (0 == 'Hello') 在 PHP 中返回 true? [英] Why does (0 == 'Hello') return true in PHP?

问题描述

嘿，如果您有以下代码并想检查 $key 是否匹配 Hello 我发现，比较总是返回 true 如果变量是 0.当一个特殊键的数组时，我遇到了这个问题，并想知道为什么它没有按预期工作.有关示例，请参阅此代码.

Hey, if you have got the following code and want to check if $key matches Hello I've found out, that the comparison always returns true if the variable is 0. I've came across this when an array for a special key and wondered why it's wasn't working as expected. See this code for an example.

$key = 1;
if ($key != 'Hello') echo 'Hello'; //echoes hello

$key = 2;
if ($key != 'Hello') echo 'Hello'; //echoes hello

$key = 0;
if ($key != 'Hello') echo '0Hello'; //doesnt echo hello. why?
if ($key !== 'Hello') echo 'Hello'; //echoes hello

谁能解释一下?

推荐答案

运算符 == 和 != 不比较类型.因此 PHP 会自动将 'Hello' 转换为 0 (intval('Hello')) 的整数.如果不确定类型，请使用类型比较运算符 === 和 !==.或者最好确定您在程序中的任何时候处理哪种类型.

The operators == and != do not compare the type. Therefore PHP automatically converts 'Hello' to an integer which is 0 (intval('Hello')). When not sure about the type, use the type-comparing operators === and !==. Or better be sure which type you handle at any point in your program.

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