#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <assert.h>

// union fields all share the same space in memory
union IntOrString {
    char* as_string;
    int as_int;
};

// unions do not know which field you are using
void print_int_or_string(union IntOrString ios) {
    // how do I know which one it is?
}

int main(int argc, char* argv[]) {
    union IntOrString ios = { .as_int = 5 };

    printf("ios.as_int == %d\n", ios.as_int);
    // seg fault: address 5 is not accessible
    //printf("ios.as_string == %s\n", ios.as_string);

    // could also use a data string, but a stack string gives
    // a bigger address for this example
    char stack_string[] = "Hello";
    ios.as_string = stack_string;
    printf("ios.as_string == %s\n", ios.as_string);
    // .as_int got overwritten when we modified .as_string
    printf("ios.as_int == %d\n", ios.as_int);

    // just to demonstrate: the int in the union is still 4 bytes
    // .as_int is not the full address .as_string as an int
    // note: normally we use %p for addresses, but this cast is safe
    printf("address of string as long %ld\n", (long)ios.as_string);

    return EXIT_SUCCESS;
}
/* vim: set tabstop=4 shiftwidth=4 fileencoding=utf-8 noexpandtab: */