union in C++

In C++. A union is defined starting with the keyword union, followed by an (optional) name for the union and a set of member declarations enclosed in curly braces.
* A union type can't have a base class. 
```
#include <iostream>
using namespace std;

union Token {
    char cval;
    int ival;
    double dval;
};

int main()
{
    Token t;
    t.cval = 1;
    cout << t.ival << endl;
}
```