isset（$ var）==“Test”和isset（$ var）&& $ var =='Test“之间的区别是什么？

Question

What is the difference between isset($var) == "Test" and isset($var) && $var == 'Test"?

Answer 1

Here a short example:

$var = "Chuck Test";

var_dump(isset($var)); // bool(true)
var_dump(isset($undefined)); // bool(false)

var_dump(isset($var) == "Chuck Test"); // bool(true)
var_dump(isset($var) && $var == "Chuck Test"); // bool(true)
var_dump(isset($undefined) == "Chuck Test"); // bool(false)
var_dump(isset($undefined) && $undefined == "Chuck Test"); // bool(false)

it looks like they are equivalent but they aren't:

var_dump(isset($var) == "Chuck Testa"); // bool(true) !!!
var_dump(isset($var) && $var == "Chuck Testa"); // bool(false)

because isset() returns true or false, and an non-empty string compared to true results in true.

So better use the isset($var) && $var == "Test" variant, because it does what you would expect.