Standard library header <utility>

 

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Language support <cfloat> <climits> <compare> (C++20) <coroutine> (C++20) <csetjmp> <csignal> <cstdarg> <cstddef> <cstdint> (C++11) <cstdlib> <exception> <initializer_list> (C++11)    <limits> <new> <source_location> (C++20) <stdfloat> (C++23) <typeinfo> <version> (C++20) Concepts <concepts> (C++20) Diagnostics <cassert> <cerrno> <debugging> (C++26) <stacktrace> (C++23) <stdexcept> <system_error> (C++11) Memory management <memory> <memory_resource> (C++17) <scoped_allocator> (C++11) Metaprogramming <type_traits> (C++11) <ratio> (C++11)

General utilities <any> (C++17) <bitset> <bit> (C++20) <charconv> (C++17) <expected> (C++23) <format> (C++20) <functional> <optional> (C++17) <tuple> (C++11) <typeindex> (C++11) <utility> <variant> (C++17) Containers <array> (C++11) <deque> <flat_map> (C++23) <flat_set> (C++23) <forward_list> (C++11) <inplace_vector> (C++26)    <list> <map> <mdspan> (C++23) <queue> <set> <span> (C++20) <stack> <unordered_map> (C++11) <unordered_set> (C++11) <vector> Iterators <iterator> Ranges <generator> (C++23) <ranges> (C++20)

Algorithms <algorithm> <numeric> Strings <cctype> <cstring> <cuchar> (C++11) <cwchar> <cwctype> <string_view> (C++17) <string> Text processing <clocale> <codecvt> (C++11/17/26*) <locale> <regex> (C++11) <text_encoding> (C++26)    Numerics <cfenv> (C++11) <cmath> <complex> <linalg> (C++26) <numbers> (C++20) <random> (C++11) <valarray> Time <chrono> (C++11) <ctime> C compatibility <ccomplex> (C++11/17/20*) <ciso646> (until C++20) <cstdalign> (C++11/17/20*) <cstdbool> (C++11/17/20*) <ctgmath> (C++11/17/20*)

Input/output <cinttypes> (C++11) <cstdio> <filesystem> (C++17) <fstream> <iomanip> <iosfwd> <iostream> <ios> <istream> <ostream> <print> (C++23) <spanstream> (C++23) <sstream> <streambuf> <strstream> (C++98/26*) <syncstream> (C++20) Concurrency support <atomic> (C++11) <barrier> (C++20) <condition_variable> (C++11) <future> (C++11) <hazard_pointer> (C++26) <latch> (C++20) <mutex> (C++11) <rcu> (C++26) <semaphore> (C++20) <shared_mutex> (C++14) <stdatomic.h> (C++23) <stop_token> (C++20) <thread> (C++11) Execution support <execution> (C++17)

 

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 and use the type template argument to preserve its value category (function template)
move (C++11)	converts the argument to an xvalue (function template)
move_if_noexcept (C++11)	converts the argument to an xvalue 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 an object of the template type argument for use in an unevaluated context (function template)
make_pair	creates a pair object of type, determined by the argument types (function template)
operator==operator!=operator<operator<=operator>operator>=operator<=> (removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(C++20)	lexicographically compares the values in the pair (function template)
std::swap(std::pair) (C++11)	specializes the std::swap algorithm (function template)
get(std::pair) (C++11)	accesses an element of a pair (function template)
as_const (C++17)	obtains a reference to const to its argument (function template)
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)
Helpers
piecewise_construct_t (C++11)	tag type used to select correct function overload for piecewise construction (class)
piecewise_constructpiecewise_construct_t (C++11)	piecewise construction tag (tag)
in_placein_place_typein_place_indexin_place_tin_place_type_tin_place_index_t (C++17)	in-place construction tag (tag)
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_tag {
    in_place_tag() = delete;
  };
  using in_place_t = in_place_tag(&)(unspecified );
  template <class T>
  using in_place_type_t = in_place_tag(&)(unspecified <T>);
  template <size_t I>
  using in_place_index_t = in_place_tag(&)(unspecified <I>);
  in_place_tag in_place(unspecified );
  template <class T>
  in_place_tag in_place(unspecified <T>);
  template <size_t I>
  in_place_tag in_place(unspecified <I>);
}

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