NAME¶

std::is_object - std::is_object

Synopsis¶

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

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

Inherited from std::integral_constant

Member constants¶

value true if T is an object 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>

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¶

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