On: Lesser known tricks, quirks and features of C

[rramadass]

This is actually pretty useful in some usecases. One very good example is Simon Tatham's "Coroutines in C" (https://www.chiark.greenend.org.uk/~sgtatham/coroutines.html) to resume execution in a function after the point it returned from in the earlier call.

The relevant example code is;

  int function(void) {
    static int i, state = 0;
    switch (state) {
        case 0: goto LABEL0;
        case 1: goto LABEL1;
    }
    LABEL0: /* start of function */
    for (i = 0; i < 10; i++) {
        state = 1; /* so we will come back to LABEL1 */
        return i;
        LABEL1:; /* resume control straight after the return */
    }
  }

becomes;

  int function(void) {
    static int i, state = 0;
    switch (state) {
        case 0: /* start of function */
        for (i = 0; i < 10; i++) {
            state = 1; /* so we will come back to "case 1"*/
            return i;
            case 1:; /* resume control straight after the return */
        }
    }
   }