std::is_lvalue_reference

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

std::is_lvalue_reference is a 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 is undefined.

Template parameters

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

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

Docs

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