std::is_union
From cppreference.com
                    
                                        
                    
                    
                                                            
                    | 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.
| Contents | 
[edit] Template parameters
| T | - | a type to check | 
Inherited from std::integral_constant
Member constants
| value [static] | true if Tis 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
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
[edit] See also
| (C++11) | checks if a type is a class type (but not union type) (class template) | 


