Standard library header <type_traits>

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Technical Specifications

 

Standard Library header files

Language Support
<cstddef> <limits> <climits> <cfloat> <cstdint> <new> <typeinfo> <exception> <ciso646>	<initializer_list> <csignal> <csetjmp> <cstdalign> <cstdarg> <cstdbool> <cstdlib> <ctime>
Diagnostics
<stdexcept> <cassert>	<cerrno> <system_error>
General utilities
<utility> <tuple> <bitset> <memory> <cstdlib> <cstring> <functional>	<type_traits> <ratio> <chrono> <ctime> <scoped_allocator> <typeindex>
Strings
<string> <cctype> <cwctype> <cstring>	<cwchar> <cstdlib> <cuchar>
Localization
<locale> <codecvt> <clocale>

Containers
<array> <deque> <forward_list> <list> <vector>	<map> <set> <unordered_map> <unordered_set> <queue> <stack>
Iterators
<iterator>
Algorithms
<algorithm>	<cstdlib>
Numerics
<cfenv> <complex> <random> <valarray>	<numeric> <cmath> <ctgmath> <cstdlib>
Input/Output
<iosfwd> <iostream> <ios> <streambuf> <istream> <ostream>	<iomanip> <sstream> <fstream> <cstdio> <cinttypes>
Regular expressions
<regex>
Thread support
<thread> <mutex> <atomic>	<shared_mutex> <condition_variable> <future>

 

This header is part of the type support library.

Classes
Helper Classes
integral_constantbool_constant (C++11)(C++17)	compile-time constant of specified type with specified value (class template)
true_type	std::integral_constant<bool, true>
false_type	std::integral_constant<bool, false>
Primary type categories
is_void (C++11)	checks if a type is void (class template)
is_null_pointer (C++14)	checks if a type is std::nullptr_t (class template)
is_integral (C++11)	checks if a type is integral type (class template)
is_floating_point (C++11)	checks if a type is floating-point type (class template)
is_array (C++11)	checks if a type is an array type (class template)
is_enum (C++11)	checks if a type is an enumeration type (class template)
is_union (C++11)	checks if a type is an union type (class template)
is_class (C++11)	checks if a type is a class type (but not union type) (class template)
is_function (C++11)	checks if a type is a function type (class template)
is_pointer (C++11)	checks if a type is a pointer type (class template)
is_lvalue_reference (C++11)	checks if a type is lvalue reference (class template)
is_rvalue_reference (C++11)	checks if a type is rvalue reference (class template)
is_member_object_pointer (C++11)	checks if a type is a pointer to a non-static member object (class template)
is_member_function_pointer (C++11)	checks if a type is a pointer to a non-static member function (class template)
Composite type categories
is_fundamental (C++11)	checks if a type is fundamental type (class template)
is_arithmetic (C++11)	checks if a type is arithmetic type (class template)
is_scalar (C++11)	checks if a type is scalar type (class template)
is_object (C++11)	checks if a type is object type (class template)
is_compound (C++11)	checks if a type is compound type (class template)
is_reference (C++11)	checks if a type is either lvalue reference or rvalue reference (class template)
is_member_pointer (C++11)	checks if a type is a pointer to a non-static member function or object (class template)
Type properties
is_const (C++11)	checks if a type is const-qualified (class template)
is_volatile (C++11)	checks if a type is volatile-qualified (class template)
is_trivial (C++11)	checks if a type is trivial (class template)
is_trivially_copyable (C++11)	checks if a type is trivially copyable (class template)
is_standard_layout (C++11)	checks if a type is standard-layout type (class template)
is_pod (C++11)	checks if a type is plain-old data (POD) type (class template)
is_literal_type (C++11)	checks if a type is literal type (class template)
is_empty (C++11)	checks if a type is class (but not union) type and has no data (class template)
is_polymorphic (C++11)	checks if a type is polymorphic class type (class template)
is_abstract (C++11)	checks if a type is abstract class type (class template)
is_signed (C++11)	checks if a type is signed arithmetic type (class template)
is_unsigned (C++11)	checks if a type is unsigned arithmetic type (class template)

Supported operations
is_constructibleis_trivially_constructibleis_nothrow_constructible (C++11)(C++11)(C++11)	checks if a type has a constructor for specific arguments (class template)
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)
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)
is_move_constructibleis_trivially_move_constructibleis_nothrow_move_constructible (C++11)(C++11)(C++11)	checks if a type has a move constructor (class template)
is_assignableis_trivially_assignableis_nothrow_assignable (C++11)(C++11)(C++11)	checks if a type has a assignment operator for a specific argument (class template)
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)
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)
is_destructibleis_trivially_destructibleis_nothrow_destructible (C++11)(C++11)(C++11)	checks if a type has a non-deleted destructor (class template)
has_virtual_destructor (C++11)	checks if a type has a virtual destructor (class template)

Property queries
alignment_of (C++11)	obtains the type's alignment requirements (class template)
rank (C++11)	obtains the number of dimensions of an array type (class template)
extent (C++11)	obtains the size of an array type along a specified dimension (class template)

Type relationships
is_same (C++11)	checks if two types are the same (class template)
is_base_of (C++11)	checks if a type is derived from the other type (class template)
is_convertible (C++11)	checks if a type can be converted to the other type (class template)
Const-volatility specifiers
remove_cvremove_constremove_volatile (C++11)(C++11)(C++11)	removes const or/and volatile specifiers from the given type (class template)
add_cvadd_constadd_volatile (C++11)(C++11)(C++11)	adds const or/and volatile specifiers to the given type (class template)
References
remove_reference (C++11)	removes reference from the given type (class template)
add_lvalue_referenceadd_rvalue_reference (C++11)(C++11)	adds lvalue or rvalue reference to the given type (class template)
Pointers
remove_pointer (C++11)	removes pointer from the given type (class template)
add_pointer (C++11)	adds pointer to the given type (class template)
Sign modifiers
make_signed (C++11)	makes the given integral type signed (class template)
make_unsigned (C++11)	makes the given integral type unsigned (class template)
Arrays
remove_extent (C++11)	removes one extent from the given array type (class template)
remove_all_extents (C++11)	removes all extents from the given array type (class template)
Miscellaneous transformations
aligned_storage (C++11)	defines the type suitable for use as uninitialized storage for types of given size (class template)
aligned_union (C++11)	defines the type suitable for use as uninitialized storage for all given types (class template)
decay (C++11)	applies type transformations as when passing a function argument by value (class template)
enable_if (C++11)	hides a function overload or template specialization based on compile-time boolean (class template)
conditional (C++11)	chooses one type or another based on compile-type boolean (class template)
common_type (C++11)	deduces the result type of a mixed-mode arithmetic expression (class template)
underlying_type (C++11)	obtains the underlying integer type for a given enumeration type (class template)
result_of (C++11)	deduces the return type of a function call expression (class template)

Synopsis

namespace std {
    // helper class:
    template <class T, T v> struct integral_constant;
    typedef integral_constant<bool, true> true_type;
    typedef integral_constant<bool, false> false_type;
    // primary type categories:
    template <class T> struct is_void;
    template <class T> struct is_null_pointer;
    template <class T> struct is_integral;
    template <class T> struct is_floating_point;
    template <class T> struct is_array;
    template <class T> struct is_pointer;
    template <class T> struct is_lvalue_reference;
    template <class T> struct is_rvalue_reference;
    template <class T> struct is_member_object_pointer;
    template <class T> struct is_member_function_pointer;
    template <class T> struct is_enum;
    template <class T> struct is_union;
    template <class T> struct is_class;
    template <class T> struct is_function;
    // composite type categories:
    template <class T> struct is_reference;
    template <class T> struct is_arithmetic;
    template <class T> struct is_fundamental;
    template <class T> struct is_object;
    template <class T> struct is_scalar;
    template <class T> struct is_compound;
    template <class T> struct is_member_pointer;
    // type properties:
    template <class T> struct is_const;
    template <class T> struct is_volatile;
    template <class T> struct is_trivial;
    template <class T> struct is_trivially_copyable;
    template <class T> struct is_standard_layout;
    template <class T> struct is_pod;
    template <class T> struct is_literal_type;
    template <class T> struct is_empty;
    template <class T> struct is_polymorphic;
    template <class T> struct is_abstract;
    template <class T> struct is_signed;
    template <class T> struct is_unsigned;
    template <class T, class... Args> struct is_constructible;
    template <class T> struct is_default_constructible;
    template <class T> struct is_copy_constructible;
    template <class T> struct is_move_constructible;
    template <class T, class U> struct is_assignable;
    template <class T> struct is_copy_assignable;
    template <class T> struct is_move_assignable;
    template <class T> struct is_destructible;
    template <class T, class... Args> struct is_trivially_constructible;
    template <class T> struct is_trivially_default_constructible;
    template <class T> struct is_trivially_copy_constructible;
    template <class T> struct is_trivially_move_constructible;
    template <class T, class U> struct is_trivially_assignable;
    template <class T> struct is_trivially_copy_assignable;
    template <class T> struct is_trivially_move_assignable;
    template <class T> struct is_trivially_destructible;
    template <class T, class... Args> struct is_nothrow_constructible;
    template <class T> struct is_nothrow_default_constructible;
    template <class T> struct is_nothrow_copy_constructible;
    template <class T> struct is_nothrow_move_constructible;
    template <class T, class U> struct is_nothrow_assignable;
    template <class T> struct is_nothrow_copy_assignable;
    template <class T> struct is_nothrow_move_assignable;
    template <class T> struct is_nothrow_destructible;
    template <class T> struct has_virtual_destructor;
    // type property queries:
    template <class T> struct alignment_of;
    template <class T> struct rank;
    template <class T, unsigned I = 0> struct extent;
    // type relations:
    template <class T, class U> struct is_same;
    template <class Base, class Derived> struct is_base_of;
    template <class From, class To> struct is_convertible;
    // const-volatile modifications:
    template <class T> struct remove_const;
    template <class T> struct remove_volatile;
    template <class T> struct remove_cv;
    template <class T> struct add_const;
    template <class T> struct add_volatile;
    template <class T> struct add_cv;
    template <class T>
    using remove_const_t = typename remove_const<T>::type;
    template <class T>
    using remove_volatile_t = typename remove_volatile<T>::type;
    template <class T>
    using remove_cv_t = typename remove_cv<T>::type;
    template <class T>
    using add_const_t = typename add_const<T>::type;
    template <class T>
    using add_volatile_t = typename add_volatile<T>::type;
    template <class T>
    using add_cv_t = typename add_cv<T>::type;
    // reference modifications:
    template <class T> struct remove_reference;
    template <class T> struct add_lvalue_reference;
    template <class T> struct add_rvalue_reference;
    template <class T>
    using remove_reference_t = typename remove_reference<T>::type;
    template <class T>
    using add_lvalue_reference_t = typename add_lvalue_reference<T>::type;
    template <class T>
    using add_rvalue_reference_t = typename add_rvalue_reference<T>::type;
    // sign modifications:
    template <class T> struct make_signed;
    template <class T> struct make_unsigned;
    template <class T>
    using make_signed_t = typename make_signed<T>::type;
    template <class T>
    using make_unsigned_t = typename make_unsigned<T>::type;
    // array modifications:
    template <class T> struct remove_extent;
    template <class T> struct remove_all_extents;
    template <class T>
    using remove_extent_t = typename remove_extent<T>::type;
    template <class T>
    using remove_all_extents_t = typename remove_all_extents<T>::type;
    // pointer modifications:
    template <class T> struct remove_pointer;
    template <class T> struct add_pointer;
    template <class T>
    using remove_pointer_t = typename remove_pointer<T>::type;
    template <class T>
    using add_pointer_t = typename add_pointer<T>::type;
    // other transformations:
    template <std::size_t Len,
              std::size_t Align = /*default-alignment*/>
    struct aligned_storage;
    template <class T> struct decay;
    template <bool, class T = void> struct enable_if;
    template <bool, class T, class F> struct conditional;
    template <class... T> struct common_type;
    template <class T> struct underlying_type;
    template <class> class result_of; // not defined
    template <class F, class... ArgTypes> class result_of<F(ArgTypes...)>;
 
    template <std::size_t Len,
              std::size_t Align = /*default-alignment*/>
    using aligned_storage_t = typename aligned_storage<Len,Align>::type;
    template <std::size_t Len, class... Types>
    using aligned_union_t = typename aligned_union<Len,Types...>::type;
    template <class T>
    using decay_t = typename decay<T>::type;
    template <bool b, class T = void>
    using enable_if_t = typename enable_if<b,T>::type;
    template <bool b, class T, class F>
    using conditional_t = typename conditional<b,T,F>::type;
    template <class... T>
    using common_type_t = typename common_type<T...>::type;
    template <class T>
    using underlying_type_t = typename underlying_type<T>::type;
    template <class T>
    using result_of_t = typename result_of<T>::type;
} // namespace std

Class std::integral_constant

template <class T, T v>
struct integral_constant {
    static constexpr T value = v;
    typedef T value_type;
    typedef integral_constant<T,v> type;
    constexpr operator value_type() const noexcept { return value; }
    constexpr value_type operator()() const noexcept { return value; } //since c++14
};
typedef integral_constant<bool, true> true_type;
typedef integral_constant<bool, false> false_type;