PHP如果执行

Question

In PHP if you have the following code does $b get evaluated since $a will cause the if statement to return false?

$a = false;
$b = true;

if ($a && $b) {
  // more code here
}

also if $b does get evaluated are there ever circumstances where a portion of an if statement may not be evaluated as the processor already knows that the value to be false?

Answer 1

Evaluation of && is stopped as soon as it hits the false condition.

These (&&) are short-circuit operators, so they don't go to check second condition if the first one true (in case of OR) or false(in case of AND).

Reference: http://php.net/manual/en/language.operators.logical.php

---

From documentation:

<?php

// --------------------
// foo() will never get called as those operators are short-circuit

$a = (false && foo());
$b = (true  || foo());
$c = (false and foo());
$d = (true  or  foo());