std::is_union

 

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is_move_constructibleis_trivially_move_constructibleis_nothrow_move_constructible (C++11)(C++11)(C++11)
is_assignableis_trivially_assignableis_nothrow_assignable (C++11)(C++11)(C++11)
is_copy_assignableis_trivially_copy_assignableis_nothrow_copy_assignable (C++11)(C++11)(C++11)
is_move_assignableis_trivially_move_assignableis_nothrow_move_assignable (C++11)(C++11)(C++11)
is_destructibleis_trivially_destructibleis_nothrow_destructible (C++11)(C++11)(C++11)
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Type transformations
aligned_storage (C++11) aligned_union (C++11) decay (C++11) enable_if (C++11) void_t (C++17)	conditional (C++11) common_type (C++11) underlying_type (C++11) result_ofinvoke_result (C++11)(deprecated in C++17)(C++17)

 

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

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

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>

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 (C++11)

checks if a type is a non-union class type (class template)