How an 'if (A && B)' statement is evaluated?

Question

if( (A) && (B) )
{
  //do something
}
else
  //do something else

The question is, would the statement immediately break to else if A was FALSE. Would B even get evaluated?

I ask this in the case that B checking the validity of an array index say array[0] when the array is actually empty and has zero elements. Therefore throwing a segfault because we are trying to access something that is out of bounds of the array. Specifically

if( (array.GetElements() > 0) && (array[0]))
  array[0]->doSomething();
else
  //do nothing and return

This may be dangerous if array[0] actually gets evaluated because it segfaults without the first check to the left of the '&&'. Precedence tells me that the left side will definitely take precedence but it doesn't tell me that it won't evaluate the right side if the left is FALSE.

Answer 1

In C and C++, the && and || operators "short-circuit". That means that they only evaluate a parameter if required. If the first parameter to && is false, or the first to || is true, the rest will not be evaluated.

The code you posted is safe, though I question why you'd include an empty else block.

Answer 2

You are asking about the && operator, not the if statement.

&& short-circuits, meaning that if while working it meets a condition which results in only one answer, it will stop working and use that answer.

So, 0 && x will execute 0, then terminate because there is no way for the expression to evaluate non-zero regardless of what is the second parameter to &&.