std:: is_union

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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.

Template parameters

T - a type to check

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

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 <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() {}

See also

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