Question

I am interested if there is any difference from the C or C++ compiler perspective whether I use:

if (value == a) {
    ...
}
else if (value == b) { 
    ...
}
else if (value == c) { 
    ...
}

versus

switch (value) {
    case a:
        ...
        break;
    case b:
        ...
        break;
    case c:
        ...
        break;
}

It feels to me that there is no difference, just syntactic. Does anyone know more about it?

Thanks, Boda Cydo.

Answer 1

There is a difference – with switch’es, the compiler may optimize the switch to use a lookup table. This may be possible if there are many values which are close enough to each other. For example, this switch:

switch ( integer ) {
  case 10:
     xxx
     break;
  case 12:
     yyy
     break;
  case 13
     zzz
     break;
}

could become (pseudocode):

address = lookup[ integer - 10 ]; // which is prefilled with { case_10, err, err, case_12, case 13 }
goto address;
case_10: xxx; goto err;
case_12: yyy; goto err;
case_13: zzz; 
err: //do nothing