std::is_lvalue_reference

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Feature test macros(C++20)
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Concepts library(C++20)
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Metaprogramming library(C++11)
General utilities library
Containers library
Iterators library
Ranges library(C++20)
Algorithms library
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Date and time library
Input/output library
Filesystem library(C++17)
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Metaprogramming library

Type traits

Type categories

is_void

(C++11)

is_null_pointer

(C++11)(DR*)

is_array (C++11)
is_pointer (C++11)
is_enum (C++11)
is_union (C++11)
is_class (C++11)
is_function (C++11)
is_reference (C++11)

is_object (C++11)
is_scalar (C++11)
is_compound (C++11)
is_integral (C++11)
is_floating_point (C++11)
is_fundamental (C++11)
is_arithmetic (C++11)

is_lvalue_reference

(C++11)

is_rvalue_reference

(C++11)

is_member_pointer

(C++11)

is_member_object_pointer

(C++11)

is_member_function_pointer

(C++11)

Type properties

(C++11)

(C++11)

(C++11)

(C++11)

(C++14)

(C++11)

(C++17)

(C++23)

(C++11)(deprecated in C++26)

is_trivially_copyable

(C++11)

is_standard_layout

(C++11)

is_literal_type

(C++11)(until C++20*)

is_pod

(C++11)(deprecated in C++20)

(C++11)

(C++11)

(C++20)

(C++20)

(C++23)

has_unique_object_representations

(C++17)

Type trait constants

integral_constantbool_constanttrue_typefalse_type

(C++11)(C++17)(C++11)(C++11)

Metafunctions

conjunction

(C++17)

disjunction

(C++17)

negation

(C++17)

Supported operations

is_constructibleis_trivially_constructibleis_nothrow_constructible (C++11)(C++11)(C++11)
is_default_constructibleis_trivially_default_constructibleis_nothrow_default_constructible (C++11)(C++11)(C++11)
is_copy_constructibleis_trivially_copy_constructibleis_nothrow_copy_constructible (C++11)(C++11)(C++11)
is_move_constructibleis_trivially_move_constructibleis_nothrow_move_constructible (C++11)(C++11)(C++11)
is_assignableis_trivially_assignableis_nothrow_assignable (C++11)(C++11)(C++11)

is_copy_assignableis_trivially_copy_assignableis_nothrow_copy_assignable (C++11)(C++11)(C++11)
is_move_assignableis_trivially_move_assignableis_nothrow_move_assignable (C++11)(C++11)(C++11)
is_destructibleis_trivially_destructibleis_nothrow_destructible (C++11)(C++11)(C++11)
has_virtual_destructor (C++11)
is_swappable_withis_swappableis_nothrow_swappable_withis_nothrow_swappable (C++17)(C++17)(C++17)(C++17)

Relationships and property queries

is_same (C++11)
is_convertibleis_nothrow_convertible (C++11)(C++20)
is_layout_compatible (C++20)
is_pointer_interconvertible_base_of (C++20)
is_pointer_interconvertible_with_class (C++20)
is_corresponding_member (C++20)
reference_constructs_from_temporary (C++23)
reference_converts_from_temporary (C++23)

is_base_of (C++11)
is_virtual_base_of (C++26)
alignment_of (C++11)
rank (C++11)
extent (C++11)
is_invocableis_invocable_ris_nothrow_invocableis_nothrow_invocable_r (C++17)(C++17)(C++17)(C++17)

Type modifications

remove_cvremove_constremove_volatile (C++11)(C++11)(C++11)
add_cvadd_constadd_volatile (C++11)(C++11)(C++11)
make_signed (C++11)
make_unsigned (C++11)

remove_reference (C++11)
add_lvalue_referenceadd_rvalue_reference (C++11)(C++11)
remove_pointer (C++11)
add_pointer (C++11)
remove_extent (C++11)
remove_all_extents (C++11)

Type transformations

aligned_storage (C++11)(deprecated in C++23)
aligned_union (C++11)(deprecated in C++23)
decay (C++11)
remove_cvref (C++20)
result_ofinvoke_result (C++11)(until C++20*)(C++17)

conditional (C++11)
common_type (C++11)
common_reference (C++20)
underlying_type (C++11)
type_identity (C++20)
enable_if (C++11)
void_t (C++17)

Compile-time rational arithmetic

Compile-time integer sequences

integer_sequence

(C++14)

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

std::is_lvalue_reference is aUnaryTypeTrait.

Checks whetherT is an lvalue reference type. Provides the member constantvalue which is equal totrue, ifT is an lvalue reference type. Otherwise,value is equal tofalse.

If the program adds specializations forstd::is_lvalue_reference orstd::is_lvalue_reference_v, the behavior is undefined.

[edit]Template parameters

a type to check

[edit]Helper variable template

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

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Inherited fromstd::integral_constant

Member constants

value

[static]

true ifT is an lvalue reference type,false otherwise
(public static member constant)

Member functions

operator bool	converts the object tobool, returnsvalue (public member function)
operator() (C++14)	returnsvalue (public member function)

Member types

Type	Definition
`value_type`	bool
`type`	std::integral_constant<bool, value>

[edit]Possible implementation

template<class T>struct is_lvalue_reference:std::false_type{};template<class T>struct is_lvalue_reference<T&>:std::true_type{};

[edit]Example

Run this code

#include <type_traits> class A{};static_assert(std::is_lvalue_reference_v<A>==false);static_assert(std::is_lvalue_reference_v<A&>==true);static_assert(std::is_lvalue_reference_v<A&&>==false); static_assert(std::is_lvalue_reference_v<int>==false);static_assert(std::is_lvalue_reference_v<int&>==true);static_assert(std::is_lvalue_reference_v<int&&>==false); int main(){}

[edit]See also

is_reference (C++11)	checks if a type is either anlvalue reference orrvalue reference (class template)[edit]
is_rvalue_reference (C++11)	checks if a type is anrvalue reference (class template)[edit]