Question

I have found out that unions are classes in c++.

If you declare a class as a union:

union Foo    // Declare union type
{
    char   ch;

    int func(int a);

};          

Will the size of the union be 4 or 1 (assuming char size of 1 and pointers size of 4 ) ?

Answer 1

I have found out that unions are classes too in c++. (emphasis mine)

No (they are a class-type, not classes).My bad, apparently they are classes:

3.9.2/1

• […]
• unions, which are classes capable of containing objects of different types at different times
• […]

(no longer relevant) Unions can’t have virtual member functions & also can’t be used in inheritance.

Onto the answer:

The size will be large enough to accommodate the largest data member. In this case, it will likely be 1, yes.