Question

I found a bug in code (the if statement should have had “==” instad of “=”) and I have few questions.

Example code:

int i = 5;
if (i = MyFunction())  // MyFunction() returns an int; this is where bug was made
{
  // call A()
}
else
{
  // call B()
}

From what I gather it should always call A().
1. Is my assumption correct()?
2. Is this case for all/most compilers (any exceptions)?

Answer 1

1. No, it will only call A() if the assignment is considered true, i.e. non-zero.
2. Yes, this is standard. It’s not a very good way to write the code since the risk of confusion is large.

Some people flip comparisons, writing the constant to the left, to avoid the risk:

if( 12 == x )

but of course this wouldn’t have worked in your case, since it really is an assignment. Most compilers can give you a warning when this code is detected, since it’s so often a cause of bugs.