How can I create a macro to generate this code?

Question

I wrote a reverse polish notation evaluator that supports many funcions, thus I have a switch with many cases like this one:

case 'b': {
    if (stack.size() < 1) fail();
    pop(l1, stack);
    l1 = log(l1);
    push(l1, stack);
    break;
}

For all the functions that require one argument the template is the same, the only change is the case character and the l1 = ...;. How can i create a macro that generates this case.

Answer 1

Untested, but this should work:

#define THEMACRO(charfunc, functionname) \
  case charfunc: { \
      if (stack.size() < 1) fail(); \
      pop(l1, stack); \
      l1 = functionname(l1); \
      push(l1, stack); \
      break; \
  } 

Now you can write:

THEMACRO('b', log)
THEMACRO('c', someotherfunction)

instead of:

case 'b': {
    if (stack.size() < 1) fail();
    pop(l1, stack);
    l1 = log(l1);
    push(l1, stack);
    break;
}
case 'c': {
    if (stack.size() < 1) fail();
    pop(l1, stack);
    l1 = someotherfunction(l1);
    push(l1, stack);
    break;
}

But it is quite ugly to do this with macros. I'd do this differently.