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std::is_union(3)	       C++ Standard Libary		std::is_union(3)

NAME
     std::is_union - std::is_union

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

	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 >					(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
	[static] (public static member constant)

Member functions
	operator bool converts the object to bool, returns value
		      (public member function)
	operator()    returns value
	(C++14)       (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
	is_class checks if a type is a non-union class type
	(C++11)  (class template)

http://cppreference.com 	   2024.06.10			std::is_union(3)
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