PHP + JavaScript：将空字符串与0进行比较时，幕后会发生什么

Question

Because of loose typing, PHP has to cast both compared variables to the same type, if they aren't yet. What happens behind the scenes for this comparison:

$v = "" == 0;

It returns true. If the type of the first variable is internally casted to the type of the second variable, I can understand it:

$v = (int)"" === 0;

But if it were so, the inverse comparison should fail:

$w = 0 == "";

because

(string)0 = "0"

which is obviously not equal to "".

but it returns true, as well.

The same behavior can be observed with JavaScript.

So now I am asking myself: what happens there?! The only explanation for me is that both variables are casted to boolean. But in this case, ["X"] == "X" should return true, but it obviously doesn't. So, what's the magic to assume "" equal 0?

Answer 1

In PHP when using the equal it will convert the input so that the following are all equal:

0 == "" == false

Which all will pass an empty() check.

If you want to check the exact type use === instead. To answer your comment, array() is not a variable, but rather a data structure, that is why it fails the == check but passes the empty() check.