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std::is_object

Defined in header <type_traits> 
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.

The behavior of a program that adds specializations for std::is_object or std::is_object_v is undefined.

Template parameters

T - a type to check

Helper variable template

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

Inherited from std::integral_constant

Member constants

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

Member functions

operator bool
converts the object to bool, returns value
(public member function)
operator()
(C++14)
returns value
(public member function)

Member types

Type Definition
value_type bool
type std::integral_constant<bool, value>

Possible implementation

template<class T>
struct is_object : std::integral_constant<bool,
                       std::is_scalar<T>::value ||
                       std::is_array<T>::value ||
                       std::is_union<T>::value ||
                       std::is_class<T>::value> {};

Example

#include <iomanip>
#include <iostream>
#include <type_traits>
 
#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

See also

(C++11)
checks if a type is a scalar type
(class template)
(C++11)
checks if a type is an array type
(class template)
(C++11)
checks if a type is a union type
(class template)
(C++11)
checks if a type is a non-union class type
(class template)

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https://en.cppreference.com/w/cpp/types/is_object