问题描述
是否需要在循环或函数之前初始化/声明变量?
Is it necessary to initialize / declare a variable before a loop or a function?
无论我之前是否初始化/声明变量，我的代码仍然有效.
Whether I initialize / declare variable before or not my code still works.
我正在分享我的实际意思的演示代码:
I'm sharing demo code for what I actually mean:
$cars = null;
foreach ($build as $brand) {
$cars .= $brand . ",";
}
echo $cars;
或者
foreach ($build as $brand) {
$cars .= $brand . ",";
}
echo $cars;
这两段代码对我来说都是一样的，所以有必要在开始时初始化/声明一个变量吗?
Both pieces of code works same for me, so is it necessary to initialize / declare a variable at the beginning?
推荐答案
PHP 不需要它，但始终初始化变量是一个好习惯.
PHP does not require it, but it is a good practice to always initialize your variables.
如果您不使用默认值初始化变量，PHP 引擎将根据您使用变量的方式进行类型转换.这有时会导致意外行为.
If you don't initialize your variables with a default value, the PHP engine will do a type cast depending on how you are using the variable. This sometimes will lead to unexpected behaviour.
总之，在我看来，总是为你的变量设置一个默认值.
So in short, in my opinion, always set a default value for your variables.
附:在您的情况下，该值应设置为"(空字符串)，而不是 null，因为您使用它来连接其他字符串.
P.S. In your case the value should be set to "" (empty string), instead of null, since you are using it to concatenate other strings.
编辑
正如其他人 (@n-dru) 所指出的，如果您不设置默认值，则会生成通知.
As others (@n-dru) have noted, if you don't set a default value a notice will be generated.
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