std::is_union - cppreference.com

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`template< class T > struct is_union;`		(since C++11)

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

Helper variable template

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

Inherited from std::integral_constant

Member constants

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

Member functions

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

Member types

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

Example

#include <type_traits>

struct A {};
static_assert(!std::is_union_v<A>);

typedef union
{
    int a;
    float b;
} B;
static_assert(std::is_union_v<B>);

struct C { B d; };
static_assert(!std::is_union_v<C>);

static_assert(!std::is_union_v<int>);

int main() {}