std::is_union - cppreference.com (original) (raw)

| | | | | -------------------------------------- | | ------------- | | template< class T > struct is_union; | | (since C++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.

Contents

• 1 Template parameters
• 2 Helper variable template
• 3 Inherited from std::integral_constant
  • 3.1 Member constants
  • 3.2 Member functions
  • 3.3 Member types
  • 3.4 Example
  • 3.5 See also

[edit] Template parameters

[edit] 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

| | true if T is a union type, false otherwise (public static member constant) | | ----------------------------------------------------------------------------- |

Member functions

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

Member types

[edit] Example

#include   struct A {}; static_assert(!std::is_union_v);   typedef union { int a; float b; } B; static_assert(std::is_union_v);   struct C { B d; }; static_assert(!std::is_union_v);   static_assert(!std::is_union_v);   int main() {}

[edit] See also

| | checks if a type is a non-union class type (class template) [edit] | | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |