std::is_union (3) - Linux Manuals

std::is_union: std::is_union

NAME

std::is_union - std::is_union

Synopsis

Defined in header <type_traits>
template< class T > (since C++11)
struct is_union;

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.

Template parameters

T - a type to check

Helper variable template

template< class T > (since C++17)
inline constexpr bool is_union_v = is_union<T>::value;

Inherited from std::integral_constant

Member constants

value true if T is a union type , false otherwise
         (public static member constant)
[static]

Member functions

              converts the object to bool, returns value
operator bool (public member function)

operator() returns value
              (public member function)
(C++14)

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