Quit recursive function when a dynamic condition is met

Using the function from Generate all sequences of bits within hamming distance t:

void magic(char* str, int i, int changesLeft) {
        if (changesLeft == 0) {
                printf("%s\n", str);
                return;
        }
        if (i < 0) return;
        // flip current bit
        str[i] = str[i] == '0' ? '1' : '0';
        magic(str, i-1, changesLeft-1);
        // or don't flip it (flip it again to undo)
        str[i] = str[i] == '0' ? '1' : '0';
        magic(str, i-1, changesLeft);
}

I would like to quit the recursive function and return to the caller function when a certain condition occurs (if it does). So it's like my recursive function is hearing voices that might tell her to quit!

It only happens after str is printed, here:

if (changesLeft == 0) {
    printf("%s\n", str);
    if quit_now = voices();
    return;
}

How to do this (stop unfolding the recursion and return to the function caller)?

---

Attempt:

if (i < 0 || quit_now == 1) return;

just seems to block the execution and never end!

_{PS - I am interested even in c old methodologies.}