Metaprogramming library(since C++11)

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Compiler support
Freestanding and hosted
Language
Standard library
Standard library headers
Named requirements
Feature test macros(C++20)
Language support library
Concepts library(C++20)
Diagnostics library
Memory management library
Metaprogramming library(C++11)
General utilities library
Containers library
Iterators library
Ranges library(C++20)
Algorithms library
Strings library
Text processing library
Numerics library
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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C++ provides metaprogramming facilities, such as type traits, compile-time rational arithmetic, and compile-time integer sequences.

[edit]Definitions

The following types are collectively calledreferenceable types:

For any referenceable typeT, a reference to it can be created^[1].

↑For reference types, this can be done viareference collapsing.

[edit]Type traits

Type traits define compile-time template-based interfaces to query the properties of types.

Attempting to specialize a template defined in the<type_traits> header and listed in this page results in undefined behavior, except thatstd::common_typeandstd::basic_common_reference(since C++20) may be specialized as required in description.

A template defined in the<type_traits> header may be instantiated with an incomplete type unless otherwise specified, notwithstanding the general prohibition against instantiating standard library templates with incomplete types.

[edit]Base classes

Most of non-transforming type traits need to be publicly and unambiguously derived fromstd::integral_constant in order to satisfy the requirements ofUnaryTypeTrait orBinaryTypeTrait.

Defined in header`<type_traits>`
integral_constantbool_constant (C++11)(C++17)	compile-time constant of specified type with specified value (class template)[edit]

Two specializations ofstd::integral_constant for the typebool are provided:

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

[edit]Unary type traits

Unary type traits can be used to query the boolean properties of a type at compile time.

All these type traits satisfyUnaryTypeTrait, the base characteristic of each type trait is eitherstd::true_type orstd::false_type, depending on whether the corresponding condition is met.

Primary type categories
Defined in header`<type_traits>`
is_void (C++11)	checks if a type isvoid (class template)[edit]
is_null_pointer (C++11)(DR*)	checks if a type isstd::nullptr_t (class template)[edit]
is_integral (C++11)	checks if a type is an integral type (class template)[edit]
is_floating_point (C++11)	checks if a type is a floating-point type (class template)[edit]
is_array (C++11)	checks if a type is an array type (class template)[edit]
is_enum (C++11)	checks if a type is an enumeration type (class template)[edit]
is_union (C++11)	checks if a type is a union type (class template)[edit]
is_class (C++11)	checks if a type is a non-union class type (class template)[edit]
is_function (C++11)	checks if a type is a function type (class template)[edit]
is_pointer (C++11)	checks if a type is a pointer type (class template)[edit]
is_lvalue_reference (C++11)	checks if a type is anlvalue reference (class template)[edit]
is_rvalue_reference (C++11)	checks if a type is anrvalue reference (class template)[edit]
is_member_object_pointer (C++11)	checks if a type is a non-static member object pointer (class template)[edit]
is_member_function_pointer (C++11)	checks if a type is a non-static member function pointer (class template)[edit]
Composite type categories
Defined in header`<type_traits>`
is_fundamental (C++11)	checks if a type is a fundamental type (class template)[edit]
is_arithmetic (C++11)	checks if a type is an arithmetic type (class template)[edit]
is_scalar (C++11)	checks if a type is a scalar type (class template)[edit]
is_object (C++11)	checks if a type is an object type (class template)[edit]
is_compound (C++11)	checks if a type is a compound type (class template)[edit]
is_reference (C++11)	checks if a type is either anlvalue reference orrvalue reference (class template)[edit]
is_member_pointer (C++11)	checks if a type is a pointer to a non-static member function or object (class template)[edit]
Type properties
Defined in header`<type_traits>`
is_const (C++11)	checks if a type is const-qualified (class template)[edit]
is_volatile (C++11)	checks if a type is volatile-qualified (class template)[edit]
is_trivial (C++11)(deprecated in C++26)	checks if a type is trivial (class template)[edit]
is_trivially_copyable (C++11)	checks if a type is trivially copyable (class template)[edit]
is_standard_layout (C++11)	checks if a type is astandard-layout type (class template)[edit]
is_pod (C++11)(deprecated in C++20)	checks if a type is a plain-old data (POD) type (class template)[edit]
is_literal_type (C++11)(deprecated in C++17)(removed in C++20)	checks if a type is a literal type (class template)[edit]
has_unique_object_representations (C++17)	checks if every bit in the type's object representation contributes to its value (class template)[edit]
is_empty (C++11)	checks if a type is a class (but not union) type and has no non-static data members (class template)[edit]
is_polymorphic (C++11)	checks if a type is a polymorphic class type (class template)[edit]
is_abstract (C++11)	checks if a type is an abstract class type (class template)[edit]
is_final (C++14)	checks if a type is a final class type (class template)[edit]
is_aggregate (C++17)	checks if a type is an aggregate type (class template)[edit]
is_implicit_lifetime (C++23)	checks if a type is an implicit-lifetime type (class template)[edit]
is_signed (C++11)	checks if a type is a signed arithmetic type (class template)[edit]
is_unsigned (C++11)	checks if a type is an unsigned arithmetic type (class template)[edit]
is_bounded_array (C++20)	checks if a type is an array type of known bound (class template)[edit]
is_unbounded_array (C++20)	checks if a type is an array type of unknown bound (class template)[edit]
is_scoped_enum (C++23)	checks if a type is a scoped enumeration type (class template)[edit]

Supported operations
Defined in header`<type_traits>`
is_constructibleis_trivially_constructibleis_nothrow_constructible (C++11)(C++11)(C++11)	checks if a type has a constructor for specific arguments (class template)[edit]
is_default_constructibleis_trivially_default_constructibleis_nothrow_default_constructible (C++11)(C++11)(C++11)	checks if a type has a default constructor (class template)[edit]
is_copy_constructibleis_trivially_copy_constructibleis_nothrow_copy_constructible (C++11)(C++11)(C++11)	checks if a type has a copy constructor (class template)[edit]
is_move_constructibleis_trivially_move_constructibleis_nothrow_move_constructible (C++11)(C++11)(C++11)	checks if a type can be constructed from an rvalue reference (class template)[edit]
is_assignableis_trivially_assignableis_nothrow_assignable (C++11)(C++11)(C++11)	checks if a type has an assignment operator for a specific argument (class template)[edit]
is_copy_assignableis_trivially_copy_assignableis_nothrow_copy_assignable (C++11)(C++11)(C++11)	checks if a type has a copy assignment operator (class template)[edit]
is_move_assignableis_trivially_move_assignableis_nothrow_move_assignable (C++11)(C++11)(C++11)	checks if a type has a move assignment operator (class template)[edit]
is_destructibleis_trivially_destructibleis_nothrow_destructible (C++11)(C++11)(C++11)	checks if a type has a non-deleted destructor (class template)[edit]
has_virtual_destructor (C++11)	checks if a type has a virtual destructor (class template)[edit]
is_swappable_withis_swappableis_nothrow_swappable_withis_nothrow_swappable (C++17)(C++17)(C++17)(C++17)	checks if objects of a type can be swapped with objects of same or different type (class template)[edit]
reference_constructs_from_temporary (C++23)	checks if a reference is bound to a temporary in direct-initialization (class template)[edit]
reference_converts_from_temporary (C++23)	checks if a reference is bound to a temporary in copy-initialization (class template)[edit]

[edit]Property queries

Property query traits can be used to query the integral properties of a type at compile time.

All these type traits satisfyUnaryTypeTrait, the base characteristic of each type trait isstd::integral_constant<std::size_t, Value>, whereValue is the query result of the corresponding property.

Defined in header`<type_traits>`
alignment_of (C++11)	obtains the type's alignment requirements (class template)[edit]
rank (C++11)	obtains the number of dimensions of an array type (class template)[edit]
extent (C++11)	obtains the size of an array type along a specified dimension (class template)[edit]

[edit]Type relationships

Type relationship traits can be used to query relationships between types at compile time.

All these type traits satisfyBinaryTypeTrait, the base characteristic of each type trait is eitherstd::true_type orstd::false_type, depending on whether the corresponding condition is met.

Defined in header`<type_traits>`
is_same (C++11)	checks if two types are the same (class template)[edit]
is_base_of (C++11)	checks if a type is a base of the other type (class template)[edit]
is_virtual_base_of (C++26)	checks if a type is a virtual base of the other type (class template)[edit]
is_convertibleis_nothrow_convertible (C++11)(C++20)	checks if a type can be converted to the other type (class template)[edit]
is_layout_compatible (C++20)	checks if two types arelayout-compatible (class template)[edit]
is_pointer_interconvertible_base_of (C++20)	checks if a type is apointer-interconvertible (initial) base of another type (class template)[edit]
is_invocableis_invocable_ris_nothrow_invocableis_nothrow_invocable_r (C++17)	checks if a type can be invoked (as if bystd::invoke) with the given argument types (class template)[edit]

[edit]Type transformations

Type transformation traits transform one type to another following some predefined rules.

All these type traits satisfyTransformationTrait.

Const-volatility specifiers
Defined in header`<type_traits>`
remove_cvremove_constremove_volatile (C++11)(C++11)(C++11)	removesconst and/orvolatile specifiers from the given type (class template)[edit]
add_cvadd_constadd_volatile (C++11)(C++11)(C++11)	addsconst and/orvolatile specifiers to the given type (class template)[edit]
References
Defined in header`<type_traits>`
remove_reference (C++11)	removes a reference from the given type (class template)[edit]
add_lvalue_referenceadd_rvalue_reference (C++11)(C++11)	adds anlvalue orrvalue reference to the given type (class template)[edit]
Sign modifiers
Defined in header`<type_traits>`
make_signed (C++11)	obtains the corresponding signed type for the given integral type (class template)[edit]
make_unsigned (C++11)	obtains the corresponding signed type for the given integral type (class template)[edit]
Arrays
Defined in header`<type_traits>`
remove_extent (C++11)	removes one extent from the given array type (class template)[edit]
remove_all_extents (C++11)	removes all extents from the given array type (class template)[edit]
Pointers
Defined in header`<type_traits>`
remove_pointer (C++11)	removes a pointer from the given type (class template)[edit]
add_pointer (C++11)	adds a pointer to the given type (class template)[edit]
Other transformations
Defined in header`<type_traits>`
aligned_storage (since C++11)(deprecated in C++23)	defines the type suitable for use as uninitialized storage for types of given size (class template)[edit]
aligned_union (since C++11)(deprecated in C++23)	defines the type suitable for use as uninitialized storage for all given types (class template)[edit]
decay (C++11)	applies type transformations as when passing a function argument by value (class template)[edit]
remove_cvref (C++20)	combinesstd::remove_cv andstd::remove_reference (class template)[edit]
enable_if (C++11)	conditionallyremoves a function overload or template specialization from overload resolution (class template)[edit]
conditional (C++11)	chooses one type or another based on compile-time boolean (class template)[edit]
common_type (C++11)	determines the common type of a group of types (class template)[edit]
common_referencebasic_common_reference (C++20)	determines the common reference type of a group of types (class template)[edit]
underlying_type (C++11)	obtains the underlying integer type for a given enumeration type (class template)[edit]
result_ofinvoke_result (C++11)(removed in C++20)(C++17)	deduces the result type of invoking a callable object with a set of arguments (class template)[edit]
void_t (C++17)	void variadic alias template (alias template)[edit]
type_identity (C++20)	returns the type argument unchanged (class template)[edit]

[edit]Logical operations(since C++17)

Logical operator traits apply logical operators to other type traits.

Defined in header`<type_traits>`
conjunction (C++17)	variadic logical AND metafunction (class template)[edit]
disjunction (C++17)	variadic logical OR metafunction (class template)[edit]
negation (C++17)	logical NOT metafunction (class template)[edit]

[edit]Member relationships(since C++20)

Defined in header`<type_traits>`
is_pointer_interconvertible_with_class (C++20)	checks if objects of a type arepointer-interconvertible with the specified subobject of that type (function template)[edit]
is_corresponding_member (C++20)	checks if two specified members correspond to each other in the common initial subsequence of two specified types (function template)[edit]