std::is_union
From cppreference.com
| Defined in header <type_traits>
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| template< class T > struct is_union; |
(since 哋它亢++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 > inline constexpr bool is_union_v = is_union<T>::value; |
(since 哋它亢++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() (哋它亢++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
| (哋它亢++11) |
checks if a type is a non-union class type (class template) |