std::integral_constant

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Named requirements
Feature test macros(C++20)
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Concepts library(C++20)
Diagnostics library
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Metaprogramming library(C++11)
General utilities library
Containers library
Iterators library
Ranges library(C++20)
Algorithms library
Strings library
Text processing library
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Date and time library
Input/output library
Filesystem library(C++17)
Concurrency support library(C++11)
Execution control library(C++26)
Technical specifications
Symbols index
External libraries

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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, T v> struct integral_constant;		(since C++11)

std::integral_constant wraps a static constant of specified type. It is the base class for the C++ type traits.

If the program adds specializations forstd::integral_constant, the behavior is undefined.

[edit]Helper alias templates

A helper alias templatestd::bool_constant is defined for the common case whereT isbool.

template<bool B> using bool_constant= integral_constant<bool, B>;		(since C++17)

[edit]Specializations

Two typedefs for the common case whereT isbool are provided:

Defined in header`<type_traits>`
Name	Definition
`true_type`	std::integral_constant<bool,true>
`false_type`	std::integral_constant<bool,false>

[edit]Member types

Name	Definition
`value_type`	T
`type`	std::integral_constant<T, v>

[edit]Member constants

Name	Value
constexpr T value [static]	v (public static member constant)

[edit]Member functions

operator value_type	returns the wrapped value (public member function)[edit]
operator() (C++14)	returns the wrapped value (public member function)[edit]

std::integral_constant::operator value_type

constexpr operator value_type()constnoexcept;

Conversion function. Returns the wrapped value.

std::integral_constant::operator()

constexpr value_type operator()()constnoexcept;		(since C++14)

Returns the wrapped value. This function enablesstd::integral_constant to serve as a source of compile-time function objects.

[edit]Possible implementation

template<class T, T v>struct integral_constant{staticconstexpr T value= v;using value_type= T;using type= integral_constant;// using injected-class-nameconstexpr operator value_type()constnoexcept{return value;}constexpr value_type operator()()constnoexcept{return value;}// since c++14};

[edit]Notes

Feature-test macro	Value	Std	Feature
`__cpp_lib_integral_constant_callable`	`201304L`	(C++14)	`std::integral_constant::operator()`
`__cpp_lib_bool_constant`	`201505L`	(C++17)	`std::bool_constant`

[edit]Example

Run this code

#include <type_traits> using two_t= std::integral_constant<int,2>;using four_t= std::integral_constant<int,4>; static_assert(notstd::is_same_v<two_t, four_t>);static_assert(two_t::value*2== four_t::value,"2*2 != 4");static_assert(two_t()<<1== four_t()>>0,"2*2 != 4"); enumclass E{ e1, e2};using c1= std::integral_constant<E, E::e1>;using c2= std::integral_constant<E, E::e2>;static_assert(c1::value!= E::e2);static_assert(c1()== E::e1);static_assert(std::is_same_v<c2, c2>); int main(){}