Std::is_union (3) Linux Manual Page

std::is_union – std::is_union

Synopsis

Defined in header<type_traits>

    template <class T>
    (since C++ 11)

        struct is_union;

Checks whether T is a union type. Provides the member constant value, which is equal to true if T is a union type . Otherwise, value is equal to false.

Template parameters

T – a type to check

Helper variable template

template< class T > (since C++17)
inline constexpr bool is_union_v = is_union<T>::value;

Inherited from std::integral_constant

Member constants

value true if T is a union type , false otherwise
(public static member constant)
[static]

Member functions

converts the object to bool, returns value
operator bool (public member function)

operator() returns value
(public member function)
(C++14)

Member types

Type Definition
value_type bool
type std::integral_constant<bool, value>

Example

// Run this code

#include <iostream>

#include <type_traits>
struct A {
};
typedef union {
    int a;
    float b;

} B;
struct C {
    B d;
};
int main()

{
    std::cout << std::boolalpha;
    std::cout << std::is_union<A>::value << '\n';
    std::cout << std::is_union<B>::value << '\n';
    std::cout << std::is_union<C>::value << '\n';
    std::cout << std::is_union<int>::value << '\n';
}

Output:

  false
  true
  false
  false

std::is_union (3) Linux Manual Page