Union, Part 2

Now, we lets move to a little complicated example with struct inside union with multiple size:

Here is a example:

#include <iostream>

struct Vector1
{
    int a, b;
};

struct Vector2
{
    union
    {
        struct
        {
            int a,b,c,d;
        };
        struct
        {
            Vector1 x,y;
        };
    };
    
};

void printVector1(Vector1& v1) {
    std::cout << v1.a << ", " << v1.b << std::endl;
}

int main(int argc, char const *argv[])
{
    Vector2 v = {1,2,3,4};
    printVector1(v.x);
    printVector1(v.y);

    v.d = 500;
    printVector1(v.x);
    printVector1(v.y);

    return 0;
}

Try it here:

Output:

1, 2
3, 4
1, 2
3, 500

Lets explore this example:

1. Here, we created 2 structs, Vector1 and Vector2.

2. Vector1 contains two integers: a, b.

3. Vector2 contains two possible values based on union, either it will have four integers a, b, c, d or it will contain 2 Vector1.

4. Now, if we create an object of Vector2 with values {1, 2, 3, 4}.

5. This Vector2 instance can be converted into two instances of Vector1 as it was part of the vector.

6. And, if we update a value of Vector2 insrance and read it as Vector1 Instance, you will see that Vector1 data has been changes as they are referring to same memory location.