recursion - How does this C int function works without a return statement?

Question

I've this C code which I was sure it wouldn't work, but it does.

#include <stdio.h>

int* find (int* a, int val) {
    if (*a == val)
        return a;
    else
        find(a+1, val);
}

int main() {
    int a[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
    int *b;

    b = find(a, 7);

    printf("%d
", *b);

    return 0;
}

Of course, I get a warning from gcc since it lacks a return statement inside the else branch of the find function. However, it works perfectly.

Why does this happen? How does it know to return an int through the recursive function? Of course, the last calls returns an int, but I'm calling it in a void context.

Answer 1

This code is not a valid C code, and the behavior of such code is not defined.

One reason why it work may be that there is no operation after the last call in find which may result in the return value of the recursive call staying in the return register (probably eax).

But again - the behavior is undefined.