NAME¶

std::is_union - std::is_union

Synopsis¶

Defined in header <type_traits>
template< class T > (since C++11)
struct is_union;

std::is_union is a UnaryTypeTrait.

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.

If the program adds specializations for std::is_union or std::is_union_v, the
behavior is undefined.

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
[static] (public static member constant)

Member functions¶

operator bool converts the object to bool, returns value
(public member function)
operator() returns value
(C++14) (public member function)

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

See also¶

is_class checks if a type is a non-union class type
(C++11) (class template)