Standard library header <utility>

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Standard Library headers
Note: a slash '/' in a revision mark means that the header was deprecated and/or removed.
Language Support
Concepts
<concepts> (C++20)
Diagnostics
<system_error> (C++11)
General utilities
<utility>
<memory>
<memory_resource> (C++17)
<scoped_allocator> (C++11)  
<expected> (C++23)
<bitset>
<tuple> (C++11)
<optional> (C++17)
<any> (C++17)
<variant> (C++17)
<type_traits> (C++11)
<ratio> (C++11)
<chrono> (C++11)
Strings
<charconv> (C++17)
<format> (C++20)

<cwchar>
<cuchar> (C++11)

Localization
<codecvt> (C++11/17)

Containers
<span> (C++20)
<array> (C++11)
<vector>
Iterators
<iterator>
Ranges
<ranges> (C++20)
Algorithms
<execution> (C++17)
Numerics
<bit> (C++20)
<numbers> (C++20)
<cfenv> (C++11)
<cmath>
Input/Output
<cstdio>
<cinttypes> (C++11)
<strstream> (C++98/)

Regular expressions
<regex> (C++11)
Filesystem support
<filesystem> (C++17)
Thread support
<thread> (C++11)
<atomic> (C++11)
<mutex> (C++11)
<shared_mutex> (C++14)
<condition_variable> (C++11)  
<future> (C++11)
<stop_token> (C++20)
<semaphore> (C++20)

<latch> (C++20)
<barrier> (C++20)

C compatibility
<cstdbool> (C++11/17/20)
<ccomplex> (C++11/17/20)
<ctgmath> (C++11/17/20)
<cstdalign> (C++11/17/20)
<ciso646> (until C++20)
<stdatomic.h>
 

This header is part of the general utility library.

Includes

(C++20)
Three-way comparison operator support
std::initializer_list class template

Namespaces

rel_ops Provide automatic comparison operators
Defined in namespace std::rel_ops
automatically generates comparison operators based on user-defined operator== and operator<
(function template)

Functions

swaps the values of two objects
(function template)
(C++14)
replaces the argument with a new value and returns its previous value
(function template)
(C++11)
forwards a function argument
(function template)
forwards a function argument as if casting it to the value category and constness of the expression of specified type template argument
(function template)
(C++11)
obtains an rvalue reference
(function template)
obtains an rvalue reference if the move constructor does not throw
(function template)
(C++17)
obtains a reference to const to its argument
(function template)
(C++11)
obtains a reference to its argument for use in unevaluated context
(function template)
converts an enumeration to its underlying type
(function template)
compares two integer values without value change caused by conversion
(function template)
(C++20)
checks if an integer value is in the range of a given integer type
(function template)
marks unreachable point of execution
(function)
creates a pair object of type, defined by the argument types
(function template)
(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)
specializes the std::swap algorithm
(function template)
accesses an element of a pair
(function template)

Classes

implements binary tuple, i.e. a pair of values
(class template)
obtains the number of elements of a tuple-like type
(class template)
obtains the element types of a tuple-like type
(class template)
obtains the size of a pair
(class template specialization)
obtains the type of the elements of pair
(class template specialization)
implements compile-time sequence of integers
(class template)
Forward declarations
Defined in header <tuple>
(C++11)
implements fixed size container, which holds elements of possibly different types
(class template)

Helpers

tag type used to select correct function overload for piecewise construction
(class)
an object of type piecewise_construct_t used to disambiguate functions for piecewise construction
(constant)
in-place construction tag
(class template)

Synopsis

#include <compare>
#include <initializer_list>
 
namespace std {
  // swap
  template<class T>
    constexpr void swap(T& a, T& b) noexcept(/* see description */);
  template<class T, size_t N>
    constexpr void swap(T (&a)[N], T (&b)[N]) noexcept(is_nothrow_swappable_v<T>);
 
  // exchange
  template<class T, class U = T>
    constexpr 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, class U>
    constexpr /* see description */ forward_like(U&& x) 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
 
  // integer comparison functions
  template<class T, class U>
    constexpr bool cmp_equal(T t, U u) noexcept;
  template<class T, class U>
    constexpr bool cmp_not_equal(T t, U u) noexcept;
 
  template<class T, class U>
    constexpr bool cmp_less(T t, U u) noexcept;
  template<class T, class U>
    constexpr bool cmp_greater(T t, U u) noexcept;
  template<class T, class U>
    constexpr bool cmp_less_equal(T t, U u) noexcept;
  template<class T, class U>
    constexpr bool cmp_greater_equal(T t, U u) noexcept;
 
  template<class R, class T>
    constexpr bool in_range(T t) noexcept;
 
  // to_underlying
  template<class T>
    constexpr underlying_type_t<T> to_underlying(T value) noexcept;
 
  // 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 description */>;
  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)>;
 
  // class template pair
  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 common_comparison_category_t</*synth-three-way-result*/<T1>,
                                           /*synth-three-way-result*/<T2>>
      operator<=>(const pair<T1, T2>&, const pair<T1, T2>&);
 
  template<class T1, class T2>
    constexpr void swap(pair<T1, T2>& x, pair<T1, T2>& y) noexcept(noexcept(x.swap(y)));
 
  template<class T1, class T2>
    constexpr /* see description */ make_pair(T1&&, T2&&);
 
  // tuple-like access to pair
  template<class T> struct tuple_size;
  template<size_t I, class T> struct tuple_element;
 
  template<class T1, class T2> struct tuple_size<pair<T1, T2>>;
  template<size_t I, class T1, class T2> struct tuple_element<I, 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 T1, class T2>
    constexpr T1& get(pair<T1, T2>& p) noexcept;
  template<class T1, class T2>
    constexpr const T1& get(const pair<T1, T2>& p) noexcept;
  template<class T1, class T2>
    constexpr T1&& get(pair<T1, T2>&& p) noexcept;
  template<class T1, class T2>
    constexpr const T1&& get(const pair<T1, T2>&& p) noexcept;
  template<class T2, class T1>
    constexpr T2& get(pair<T1, T2>& p) noexcept;
  template<class T2, class T1>
    constexpr const T2& get(const pair<T1, T2>& p) noexcept;
  template<class T2, class T1>
    constexpr T2&& get(pair<T1, T2>&& p) noexcept;
  template<class T2, class T1>
    constexpr const T2&& get(const pair<T1, T2>&& p) noexcept;
 
  // pair piecewise construction
  struct piecewise_construct_t {
    explicit piecewise_construct_t() = default;
  };
  inline 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{};
 
  // unreachable
  [[noreturn]] void unreachable();
}
 
// deprecated
namespace std::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&);
}

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 template 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 explicit(/* see description */) pair();
    constexpr explicit(/* see description */) pair(const T1& x, const T2& y);
    template<class U1 = T1, class U2 = T2>
      constexpr explicit(/* see description */) pair(U1&& x, U2&& y);
    template<class U1, class U2>
      constexpr explicit(/* see description */) pair(const pair<U1, U2>& p);
    template<class U1, class U2>
      constexpr explicit(/* see description */) pair(pair<U1, U2>&& p);
    template<class... Args1, class... Args2>
      constexpr pair(piecewise_construct_t,
                     tuple<Args1...> first_args, tuple<Args2...> second_args);
 
    constexpr pair& operator=(const pair& p);
    template<class U1, class U2>
      constexpr pair& operator=(const pair<U1, U2>& p);
    constexpr pair& operator=(pair&& p) noexcept(/* see description */);
    template<class U1, class U2>
      constexpr pair& operator=(pair<U1, U2>&& p);
 
    constexpr void swap(pair& p) noexcept(/* see description */);
  };
 
  template<class T1, class T2>
    pair(T1, T2) -> pair<T1, T2>;
}

See also

(C++11)
std::tuple class template