std:: is_object

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C++
Metaprogramming library
Type traits
Type categories
is_object
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
Type properties
(C++11)
(C++11)
(C++11)
(C++11)
(C++14)
(C++11)
(C++17)
(C++23)
(C++11) (deprecated in C++26)
(C++11)
(C++11)
(C++11) ( until C++20* )
(C++11) (deprecated in C++20)
(C++11)
(C++11)
(C++20)
(C++20)
(C++23)
(C++17)
Type trait constants
(C++11) (C++17) (C++11) (C++11)
Metafunctions
(C++17)
(C++17)
(C++17)
Supported operations
Relationships and property queries
Type modifications
Type transformations
(C++11) (deprecated in C++23)
(C++11) (deprecated in C++23)
(C++11)
(C++20)
(C++11)
(C++17)

(C++11)
(C++11)
(C++20)
(C++11)
(C++11) ( until C++20* ) (C++17)
(C++20)
Compile-time rational arithmetic
Compile-time integer sequences
(C++14)
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 .

If the program adds specializations for std::is_object or std::is_object_v , the behavior is undefined.

Template parameters

T - a type to check

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

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

Run this code 
#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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