std::is_lvalue_reference

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

std::is_lvalue_reference is an UnaryTypeTrait.

Checks whether T is an lvalue reference type. Provides the member constant value which is equal to true, if T is an lvalue reference type. Otherwise, value is equal to false.

The behavior of a program that adds specializations for std::is_lvalue_reference or std::is_lvalue_reference_v (since C++17) is undefined.

Template parameters

T - a type to check

Helper variable template

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

Inherited from std::integral_constant

Member constants

value
[static]
 true if T is an lvalue 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_lvalue_reference     : std::false_type {};
template<class T> struct is_lvalue_reference<T&> : std::true_type {};

Example

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

Output:

false
true
false
false
true
false

See also

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