template <class T> struct is_union;

// C++ program to illustrate
// is_union template
  
#include <iostream>
#include <type_traits>
using namespace std;
  
struct GFG1 {
};
  
union GFG2 {
    int var1;
    float var2;
};
  
int main()
{
    cout << boolalpha;
    cout << "is_union:" << endl;
    cout << "GFG1: "
         << is_union<GFG1>::value << endl;
    cout << "GFG2: "
         << is_union<GFG2>::value << endl;
    return 0;
}

is_union:
GFG1: false
GFG2: true

// C++ program to illustrate
// is_union template
  
#include <iostream>
#include <type_traits>
using namespace std;
  
union GFG1 {
    int var1;
    float var2;
    char var3;
};
  
struct GFG2 {
    union {
        int var4;
        float var5;
    };
};
  
int main()
{
    cout << boolalpha;
    cout << "is_union:" << endl;
    cout << "int: "
         << is_union<int>::value << endl;
    cout << "GFG1: "
         << is_union<GFG1>::value << endl;
    cout << "GFG2: "
         << is_union<GFG2>::value << endl;
    return 0;
}

is_union:
int: false
GFG1: true
GFG2: false