isset()和PHP全局变量

问题描述

关于全局变量初始化，

function hello_testing() {
    global $conditional_random;
    if (isset($conditional_random)) {
        echo "foo is inside";
    }
}

在调用hello_testing()函数之前，可能无法初始化全局变量(conditional_random).

The global variable (conditional_random) may not be initialized before the hello_testing() function is called.

那么，当未初始化$conditional_random时，通过isset()进行的验证会如何?它会失败还是永远都是真的?

So, what happens to my validation via isset() when $conditional_random is not initialized? Will it fail or it will always be true?

推荐答案

那么，为什么不进行测试呢? ;-)

Well, why don't you just test ? ;-)

注意:这并不像您想的那么简单-阅读完整答案;-)

Note: It is not as easy as you'd think -- read the full answer ;-)

调用hello_testing();函数，而不设置变量:

Calling the hello_testing(); function, without setting the variable:

hello_testing();

我没有输出-表示返回了 isset false .

I get no output -- which indicates isset returned false.

设置变量后，调用函数:

Calling the function, after setting the variable:

$conditional_random = 'blah';
hello_testing();

我得到一个输出:

foo is inside

表明 global 可以正常工作，当变量设置为时-嗯，对此应该毫无疑问^^

但是请注意，如果设置了变量，则isset将返回false，并且null！

But note that isset will return false if a variable is set, and null!

请参见 isset() 的手册页

这意味着更好的测试是:

Which means that a better test would be:

function hello_testing() {
    global $conditional_random;
    var_dump($conditional_random);
}

hello_testing();

这将显示:

null

否注意:该变量存在！即使null.

No Notice: the variable exists! Even if null.

由于我没有在函数外部设置变量，因此它表明global 设置变量-但它没有输入值；这表示null(如果尚未在函数外部设置).

As I didn't set the variable outside of the function, it shows that global sets the variable -- but it doesn't put a value into it; which means it's null if not already set outside the function.

时间:

function hello_testing() {
    //global $conditional_random;
    var_dump($conditional_random);
}

hello_testing();

赠予:

Notice: Undefined variable: conditional_random

证明已启用通知；-)

并且，如果global没有对变量进行"设置"，那么前面的示例也会给出相同的提示.

And, if global didn't "set" the variable, the previous example would have given the same notice.

最后，

function hello_testing() {
    global $conditional_random;
    var_dump($conditional_random);
}

$conditional_random = 'glop';
hello_testing();

赠予:

string 'glop' (length=4)

(这纯粹是为了证明我的示例并未受骗^^)

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