Is there a better way to do C style error handling?

Question

I\'m trying to learn C by writing a simple parser / compiler. So far its been a very enlightening experience, however coming from a strong background in C# I\'m having some pro

Answer 1

It's a bigger problem when you have to repeat the same finalizing code before each return from an error. In such cases it is widely accepted to use goto:

int func ()
{
  if (a() < 0) {
    goto failure_a;
  }

  if (b() < 0) {
    goto failure_b;
  }

  if (c() < 0) {
    goto failure_c;
  }

  return SUCCESS;

  failure_c:
  undo_b();

  failure_b:
  undo_a();

  failure_a:
  return FAILURE;
}

You can even create your own macros around this to save you some typing, something like this (I haven't tested this though):

#define CALL(funcname, ...) \
  if (funcname(__VA_ARGS__) < 0) { \ 
    goto failure_ ## funcname; \
  }

Overall, it is a much cleaner and less redundant approach than the trivial handling:

int func ()
{
  if (a() < 0) {
    return FAILURE;
  }

  if (b() < 0) {
    undo_a();
    return FAILURE;
  }

  if (c() < 0) {
    undo_b();
    undo_a();
    return FAILURE;
  }

  return SUCCESS;
}

As an additional hint, I often use chaining to reduce the number of if's in my code:

if (a() < 0 || b() < 0 || c() < 0) {
  return FAILURE;
}

Since || is a short-circuit operator, the above would substitute three separate if's. Consider using chaining in a return statement as well:

return (a() < 0 || b() < 0 || c() < 0) ? FAILURE : SUCCESS;