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std::is_union

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Defined in header <type_traits>
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.

Contents

[edit] Template parameters

T - a type to check

[edit] Helper variable template

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

Inherited from std::integral_constant

Member constants

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

Member functions

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

Member types

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

[edit] Example

Run this code
#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() {}

[edit] See also

(C++11)
 checks if a type is a non-union class type
(class template) [edit]
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