Question

The following code prints ‘2’ four times. Why does it never print ‘1’? Can someone explain me exactly what is happening here?

#include <iostream>

int main () {

    union IntegersUnion {

        int a;
        int b;
    };

    IntegersUnion q;

    q.a = 1;
    q.b = 2;

    std::cout << "(*(&q.a)) = " << (*(&q.a)) << std::endl;
    std::cout << "(*(&q.b)) = " << (*(&q.b)) << std::endl;

    std::cout << "(*(&(q.a))) = " << (*(&(q.a))) << std::endl;
    std::cout << "(*(&(q.b))) = " << (*(&(q.b))) << std::endl;
    return 0;
}

Answer 1

A union shares the memory between its members. By doing:

q.a = 1;
q.b = 2;

the second assignment overwrites the a.