Defined in header <type_traits> | ||
---|---|---|
template< class T > struct is_union; | (since C++11) |
Checks whether T
is an union type. Provides the member constant value
which is equal to true
, if T
is an union type . Otherwise, value
is equal to false
.
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
#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
(C++11) | checks if a type is a non-union class type (class template) |
std::experimental::is_union_v
(library fundamentals TS) | variable template alias of std::is_union::value (variable template) |
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