检查IF内的条件的顺序是什么？

Question

I had a problem were I need to check two conditions, A and B. The thing is, checking B takes a lot of time, and if A is already false I don't need to check for B. I can easily do:

if(a)
  if(b)
    // Do something

But I wonder, if I do if(a AND b), does the PHP interpreter check for A and B and then apply the AND operator? Or does it already "know" there is an AND operator and so if A is false it does not checks for B?

Answer 1

What you are talking about is called Short-Circuit evaluation. I am not a PHP expert but a quick search on google explains that it is implemented in PHP. So, if A is false, B will not be executed.

http://en.wikipedia.org/wiki/Short-circuit_evaluation