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
.
T | - | a type to check |
template< class T > inline constexpr bool is_union_v = is_union<T>::value; | (since C++17) |
value
[static] | true if T is a union type , false otherwise (public static member constant) |
operator bool | converts the object to bool , returns value (public member function) |
operator()
(C++14) | returns value (public member function) |
Type | Definition |
---|---|
value_type | bool |
type | std::integral_constant<bool, value> |
#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
(C++11) | checks if a type is a non-union class type (class template) |
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