# std::is_reference

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< 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.

### 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

Run this code

    #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

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

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