std::is_union

From Cppreference

Defined in header `<type_traits>`

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

If T is a union type, provides the member constant value equal true. For any other type, value is false.

Inherited from std::integral_constant

Member constants


`value`	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)

Member types


Type	Definition

`value_type`	`bool`

`type`	std::integral_constant<bool, value>

[edit] Example

#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

[edit] See also

is_class (C++11)

checks if a type is a class type (but not union type)
(class template)