&& 之后的条件总是得到评估

I have this if statement that tests for the 2 conditions below. The second one is a function goodToGo() so I want to call it unless the first condition is already true

$value = 2239;

if ($value < 2000 && goodToGo($value)){
   //do stuff
}

function goodToGo($value){
   $ret = //some processing of the value
   return $ret; 
}

My question is about the 2 if conditions $value < 2000 && goodToGo($value). Do they both get evaluated or does the second one only get evaluated when the first one is true?

In other words, are the following 2 blocks the same?

if($value < 2000 && goodToGo($value)) {
   //stuff to do
}

if($value < 2000) {
    if (goodToGo($value)){
       //stuff to do
    }
}

解决方案

No--the second condition won't always be executed (which makes your examples equivalent).

PHP's &&, ||, and, and or operators are implemented as "short-circuit" operators. As soon as a condition is found that forces the result for the overall conditional, evaluation of subsequent conditions stops.

From http://www.php.net/manual/en/language.operators.logical.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());