Standard library header <utility>

C++

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Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

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)

Filesystem library (C++17)

Technical Specifications

Standard Library header files

Language Support
<cstddef> <limits> <climits> <contract>	<cfloat> <cstdint> <new> <version>	<typeinfo> <exception> <initializer_list>	<csignal> <csetjmp> <cstdarg>
Concepts
<concepts>
Diagnostics
<stdexcept>	<cassert>	<cerrno>	<system_error>
General utilities
<utility> <memory> <memory_resource> <scoped_allocator> <compare>	<bitset> <tuple> <optional> <any> <variant>	<type_traits> <ratio> <chrono> <typeindex> <functional>	<ctime> <cstdlib>
Strings
<string> <string_view>	<cctype> <cwctype>	<cwchar> <cuchar>	<cstring> <charconv>
Localization
<locale>	<codecvt>	<clocale>
Containers
<span> <array> <vector>	<deque> <forward_list> <list>	<map> <set> <queue>	<unordered_map> <unordered_set> <stack>
Iterators
<iterator>
Algorithms
<algorithm>	<execution>
Numerics
<complex> <random>	<valarray> <numeric>	<cfenv> <cmath>	<bit>
Input/Output
<iosfwd> <ios> <iomanip> <streambuf>	<istream> <ostream> <iostream>	<sstream> <fstream> <syncstream>	<cstdio> <cinttypes> <strstream>
Regular expressions
<regex>
Filesystem support
<filesystem>
Thread support
<thread> <atomic>	<mutex> <shared_mutex>	<condition_variable> <future>
C compatibility
<ciso646> <cstdalign>	<cstdbool> <ccomplex>	<ctgmath>

This header is part of the general utility library.

Includes
<initializer_list>(C++11)
Namespaces
rel_ops	Provide automatic comparison operators
Defined in namespace std::rel_ops
operator!=operator>operator<=operator>= (deprecated in C++20)	automatically generates comparison operators based on user-defined operator== and operator< (function template)
Functions
swap	swaps the values of two objects (function template)
exchange (C++14)	replaces the argument with a new value and returns its previous value (function template)
forward (C++11)	forwards a function argument (function template)
move (C++11)	obtains an rvalue reference (function template)
move_if_noexcept (C++11)	obtains an rvalue reference if the move constructor does not throw (function template)
as_const (C++17)	obtains a reference to const to its argument (function template)
declval (C++11)	obtains a reference to its argument for use in unevaluated context (function template)
make_pair	creates a pair object of type, defined by the argument types (function template)
operator==operator!=operator<operator<=operator>operator>=	lexicographically compares the values in the pair (function template)
std::swap(std::pair) (C++11)	specializes the std::swap algorithm (function template)
std::get(std::pair) (C++11)	accesses an element of a pair (function template)
to_chars (C++17)	converts an integer or floating-point value to a character sequence (function)
from_chars (C++17)	converts a character sequence to an integer or floating-point value (function)
Classes
pair	implements binary tuple, i.e. a pair of values (class template)
integer_sequence (C++14)	implements compile-time sequence of integers (class template)
chars_format (C++17)	specifies formatting for std::to_chars and std::from_chars (enum)
Helpers
piecewise_construct_t (C++11)	tag type used to select correct function overload for piecewise construction (class)
piecewise_construct (C++11)	an object of type piecewise_construct_t used to disambiguate functions for piecewise construction (constant)
in_place in_place_type in_place_index in_place_t in_place_type_t in_place_index_t (C++17)	in-place construction tag (class template)
Forward declarations
tuple (C++11)	implements fixed size container, which holds elements of possibly different types (class template)

Synopsis

#include <initializer_list>
namespace std {
  // operators:
  namespace rel_ops {
    template<class T> bool operator!=(const T&, const T&);
    template<class T> bool operator> (const T&, const T&);
    template<class T> bool operator<=(const T&, const T&);
    template<class T> bool operator>=(const T&, const T&);
  }
  // swap:
  template <class T>
  void swap(T& a, T& b) noexcept(/*see definition*/ );
  template <class T, size_t N>
  void swap(T (&a)[N], T (&b)[N]) noexcept(is_nothrow_swappable_v<T>);

  // exchange:
  template <class T, class U=T> T exchange(T& obj, U&& new_val);

  // forward/move:
  template <class T>
  constexpr T&& forward(remove_reference_t<T>& t) noexcept;
  template <class T>
  constexpr T&& forward(remove_reference_t<T>&& t) noexcept;
  template <class T>
  constexpr remove_reference_t<T>&& move(T&&) noexcept;
  template <class T>
  constexpr conditional_t<!is_nothrow_move_constructible_v<T>
                          && is_copy_constructible_v<T>, const T&, T&&>
  move_if_noexcept(T& x) noexcept;

  // as_const:
  template <class T> constexpr add_const_t<T>& as_const(T& t) noexcept;
  template <class T> void as_const(const T&&) = delete;

  // declval:
  template <class T>
  add_rvalue_reference_t<T> declval() noexcept; // as unevaluated operand

  // Compile-time integer sequences
  template<class T, T...> struct integer_sequence;
  template<size_t... I>
  using index_sequence = integer_sequence<size_t, I...>;
  template<class T, T N>
  using make_integer_sequence = integer_sequence<T, /*see definition*/ >;
  template<size_t N>
  using make_index_sequence = make_integer_sequence<size_t, N>;
  template<class... T>
  using index_sequence_for = make_index_sequence<sizeof...(T)>;

  // pairs:
  template <class T1, class T2> struct pair;

  // pair specialized algorithms:
  template <class T1, class T2>
  constexpr bool operator==(const pair<T1, T2>&, const pair<T1, T2>&);
  template <class T1, class T2>
  constexpr bool operator< (const pair<T1, T2>&, const pair<T1, T2>&);
  template <class T1, class T2>
  constexpr bool operator!=(const pair<T1, T2>&, const pair<T1, T2>&);
  template <class T1, class T2>
  constexpr bool operator> (const pair<T1, T2>&, const pair<T1, T2>&);
  template <class T1, class T2>
  constexpr bool operator>=(const pair<T1, T2>&, const pair<T1, T2>&);
  template <class T1, class T2>
  constexpr bool operator<=(const pair<T1, T2>&, const pair<T1, T2>&);
  template <class T1, class T2>
  void swap(pair<T1, T2>& x, pair<T1, T2>& y) noexcept(noexcept(x.swap(y)));
  template <class T1, class T2>
  constexpr /*see definition*/ make_pair(T1&&, T2&&);

  // tuple-like access to pair:
  template <class T> class tuple_size;
  template <size_t I, class T> class tuple_element;
  template <class T1, class T2> struct tuple_size<pair<T1, T2>>;
  template <class T1, class T2> struct tuple_element<0, pair<T1, T2>>;
  template <class T1, class T2> struct tuple_element<1, pair<T1, T2>>;
  template<size_t I, class T1, class T2>
  constexpr tuple_element_t<I, pair<T1, T2>>& get(pair<T1, T2>&) noexcept;
  template<size_t I, class T1, class T2>
  constexpr tuple_element_t<I, pair<T1, T2>>&& get(pair<T1, T2>&&) noexcept;
  template<size_t I, class T1, class T2>
  constexpr const tuple_element_t<I, pair<T1, T2>>& get(const pair<T1, T2>&) noexcept;
  template<size_t I, class T1, class T2>
  constexpr const tuple_element_t<I, pair<T1, T2>>&& get(const pair<T1, T2>&&) noexcept;
  template <class T, class U>
  constexpr T& get(pair<T, U>& p) noexcept;
  template <class T, class U>
  constexpr const T& get(const pair<T, U>& p) noexcept;
  template <class T, class U>
  constexpr T&& get(pair<T, U>&& p) noexcept;
  template <class T, class U>
  constexpr const T&& get(const pair<T, U>&& p) noexcept;
  template <class T, class U>
  constexpr T& get(pair<U, T>& p) noexcept;
  template <class T, class U>
  constexpr const T& get(const pair<U, T>& p) noexcept;
  template <class T, class U>
  constexpr T&& get(pair<U, T>&& p) noexcept;
  template <class T, class U>
  constexpr const T&& get(const pair<U, T>&& p) noexcept;

  // pair piecewise construction
  struct piecewise_construct_t { };
  constexpr piecewise_construct_t piecewise_construct{};
  template <class... Types> class tuple; // defined in <tuple>

  // in-place construction
  struct in_place_t { explicit in_place_t() = default; };
  inline constexpr in_place_t in_place{};
  template <class T>
  struct in_place_type_t { explicit in_place_type_t() = default; };
  template <class T>
  inline constexpr in_place_type_t<T> in_place_type{};
  template <size_t I>
  struct in_place_index_t { explicit in_place_index_t() = default; };
  template <size_t I>
  inline constexpr in_place_index_t<I> in_place_index{};
  // floating-point format for primitive numerical conversion
  enum class chars_format {
    scientific = /*unspecified*/ ,
    fixed = /*unspecified*/ ,
    hex = /*unspecified*/ ,
    general = fixed | scientific
  };
  // primitive numerical output conversion
  struct to_chars_result {
    char* ptr;
    error_code ec;
  };
  to_chars_result to_chars(char* first, char* last, see below value, int base = 10);
  to_chars_result to_chars(char* first, char* last, float value);
  to_chars_result to_chars(char* first, char* last, double value);
  to_chars_result to_chars(char* first, char* last, long double value);
  to_chars_result to_chars(char* first, char* last, float value, chars_format fmt);
  to_chars_result to_chars(char* first, char* last, double value, chars_format fmt);
  to_chars_result to_chars(char* first, char* last, long double value, chars_format fmt);
  to_chars_result to_chars(char* first, char* last, float value,
                           chars_format fmt, int precision);
  to_chars_result to_chars(char* first, char* last, double value,
                           chars_format fmt, int precision);
  to_chars_result to_chars(char* first, char* last, long double value,
                           chars_format fmt, int precision);
  // primitive numerical input conversion
  struct from_chars_result {
    const char* ptr;
    error_code ec;
  };
  from_chars_result from_chars(const char* first, const char* last,
                               /*see description*/ & value, int base = 10);
  from_chars_result from_chars(const char* first, const char* last, float& value,
                               chars_format fmt = chars_format::general);
  from_chars_result from_chars(const char* first, const char* last, double& value,
                               chars_format fmt = chars_format::general);
  from_chars_result from_chars(const char* first, const char* last, long double& value,
                               chars_format fmt = chars_format::general);
}

Class template std::integer_sequence

namespace std {
  template<class T, T... I>
  struct integer_sequence {
    using value_type = T;
    static constexpr size_t size() noexcept { return sizeof...(I); }
  };
}

Class std::pair

namespace std {
  template <class T1, class T2>
  struct pair {
    using first_type = T1;
    using second_type = T2;
    T1 first;
    T2 second;
    pair(const pair&) = default;
    pair(pair&&) = default;
    constexpr pair();
    /*conditionally-explicit*/ constexpr pair(const T1& x, const T2& y);
    template<class U, class V>
    /*conditionally-explicit*/  constexpr pair(U&& x, V&& y);
    template<class U, class V>
    /*conditionally-explicit*/  constexpr pair(const pair<U, V>& p);
    template<class U, class V>
    /*conditionally-explicit*/  constexpr pair(pair<U, V>&& p);
    template <class... Args1, class... Args2>
    pair(piecewise_construct_t, tuple<Args1...> first_args, tuple<Args2...> second_args);
    pair& operator=(const pair& p);
    template<class U, class V> pair& operator=(const pair<U, V>& p);
    pair& operator=(pair&& p) noexcept(/*see definition*/ );
    template<class U, class V> pair& operator=(pair<U, V>&& p);
    void swap(pair& p) noexcept(/*see definition*/);
  };
}

See also

<tuple>	Defines std::tuple
Utility library