std::is_reference

< cpp‎ | types
Defined in header <type_traits>
template< class T >
struct is_reference;
 (since C++11)

If T is a reference type (lvalue reference or rvalue reference), provides the member constant value equal true. For any other type, value is false.

The behavior of a program that adds specializations for is_reference or is_reference_v (since C++17) is undefined.

Template parameters

T - a type to check

Helper variable template

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

Inherited from std::integral_constant

Member constants

value
[static]
 true if T is a reference 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_reference      : std::false_type {};
template <class T> struct is_reference<T&>  : std::true_type {};
template <class T> struct is_reference<T&&> : std::true_type {};

Example

#include <iostream>
#include <type_traits>
 
class A {};
 
int main() 
{
    std::cout << std::boolalpha;
    std::cout << std::is_reference<A>::value << '\n';
    std::cout << std::is_reference<A&>::value << '\n';
    std::cout << std::is_reference<A&&>::value << '\n';
    std::cout << std::is_reference<int>::value << '\n';
    std::cout << std::is_reference<int&>::value << '\n';
    std::cout << std::is_reference<int&&>::value << '\n';
}

Output:

false
true
true
false
true
true

See also

(C++11)
 checks if a type is a lvalue reference
(class template)
(C++11)
 checks if a type is a rvalue reference
(class template)