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

| | | | | --------------------------------------- | | ------------- | | template< class T > struct is_object; | | (since C++11) |

std::is_object is a UnaryTypeTrait.

If T is an object type (that is any possibly cv-qualified type other than function, reference, or void types), provides the member constant value equal true. For any other type, value is false.

If the program adds specializations for std::is_object or std::is_object_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 Possible implementation
  • 3.5 Example
  • 3.6 See also

[edit] Template parameters

[edit] Helper variable template

| template< class T > constexpr bool is_object_v = is_object<T>::value; | | (since C++17) | | --------------------------------------------------------------------------- | | ------------- |

Inherited from std::integral_constant

Member constants

| | true if T is an object 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] Possible implementation

[edit] Example

#include #include #include   #define IS_OBJECT(...)
std::cout << std::boolalpha << std::left << std::setw(9) << #__VA_ARGS__
<< (std::is_object_v<__VA_ARGS__> ? " is object\n"
 : " is not an object\n")   int main() { class cls {};   IS_OBJECT(void); IS_OBJECT(int); IS_OBJECT(int&); IS_OBJECT(int*); IS_OBJECT(int*&); IS_OBJECT(cls); IS_OBJECT(cls&); IS_OBJECT(cls*); IS_OBJECT(int()); IS_OBJECT(int(*)()); IS_OBJECT(int(&)()); }

Output:

void is not an object int is object int& is not an object int* is object int*& is not an object cls is object cls& is not an object cls* is object int() is not an object int(*)() is object int(&)() is not an object

[edit] See also

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