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std is_union() template in C++

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The std::is_union template of C++ STL is used to check whether the given type is union or not. It returns a boolean value showing the same.

Syntax:

template <class T> struct is_union;

Parameter: This template accepts single parameter T (Trait class) to check whether T is a union or not.

Return Value: This template returns a boolean value as shown below:

  • True: If a type is a union class.
  • False: If a type is a non-union class.

Below programs illustrate the std::is_union template in C++:

Program 1::




// 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;
}


Output:

is_union:
GFG1: false
GFG2: true

Program 2:




// 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;
}


Output:

is_union:
int: false
GFG1: true
GFG2: false


Last Updated : 19 Nov, 2018
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