Is it possible to store the address of a label in a variable and use goto to jump to it?

Question

I know everyone hates gotos. In my code, for reasons I have considered and am comfortable with, they provide an effective solution (ie I\'m not looking for \"don\'t do that\

Answer 1

The switch ... case statement is essentially a computed goto. A good example of how it works is the bizarre hack known as Duff's Device:

send(to, from, count)
register short *to, *from;
register count;
{
    register n=(count+7)/8;
    switch(count%8){
    case 0: do{ *to = *from++;
    case 7:     *to = *from++;
    case 6:     *to = *from++;
    case 5:     *to = *from++;
    case 4:     *to = *from++;
    case 3:     *to = *from++;
    case 2:     *to = *from++;
    case 1:     *to = *from++;
        }while(--n>0);
    }
}

You can't do a goto from an arbitrary location using this technique, but you can wrap your entire function in a switch statement based on a variable, then set that variable indicating where you want to go, and goto that switch statement.

int main () {
  int label = 0;
  dispatch: switch (label) {
  case 0:
    label = some_computation();
    goto dispatch;
  case 1:
    label = another_computation();
    goto dispatch;
  case 2:
    return 0;
  }
}

Of course, if you do this a lot, you'd want to write some macros to wrap it.

This technique, along with some convenience macros, can even be used to implement coroutines in C.

Answer 2

You can do something like Fortran's computer goto with pointers to functions.

// global variables up here

void c1(){ // chunk of code

}

void c2(){ // chunk of code

}

void c3(){
// chunk of code

}

void (*goTo[3])(void) = {c1, c2, c3};

// then
int x = 0;

goTo[x++] ();

goTo[x++] ();

goTo[x++] ();