Standard library header <compare>

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library(C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library(C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library(C++17)

Regular expressions library(C++11)

Atomic operations library(C++11)

Thread support library(C++11)

Technical Specifications

 

Standard Library headers

Language Support
<cstddef> <cstdlib> <version> <limits> <climits>	<cfloat> <cstdint> <new> <typeinfo>	<source_location> <exception> <initializer_list> <compare>	<coroutine> <csignal> <csetjmp> <cstdarg>
Concepts
<concepts>
Diagnostics
<stdexcept>	<cassert>	<cerrno>	<system_error>
General utilities
<utility> <memory> <memory_resource> <scoped_allocator>	<bitset> <tuple> <optional> <any>	<variant> <type_traits> <ratio> <chrono>	<typeindex> <functional> <ctime>
Strings
<string> <string_view> <cstring>	<charconv> <format>	<cctype> <cwctype>	<cwchar> <cuchar>
Localization
<locale>	<codecvt>	<clocale>
Containers
<span> <array> <vector>	<deque> <forward_list> <list>	<map> <set> <queue>	<unordered_map> <unordered_set> <stack>
Iterators
<iterator>
Ranges
<ranges>
Algorithms
<algorithm>	<execution>
Numerics
<complex> <random>	<valarray> <numeric>	<bit> <numbers>	<cfenv> <cmath>
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>	<stop_token> <semaphore>	<latch> <barrier>
C compatibility
<ciso646> <cstdalign>	<cstdbool> <ccomplex>	<ctgmath>

 

This header is part of the language support library.

Concepts
three_way_comparablethree_way_comparable_with (C++20)	specifies that operator <=> produces consistent result on given types (concept)
Classes
partial_ordering (C++20)	the result type of 3-way comparison that supports all 6 operators, is not substitutable, and allows incomparable values (class)
weak_ordering (C++20)	the result type of 3-way comparison that supports all 6 operators and is not substitutable (class)
strong_ordering (C++20)	the result type of 3-way comparison that supports all 6 operators and is substitutable (class)
common_comparison_category (C++20)	the strongest comparison category to which all of the given types can be converted (class template)
compare_three_way_result (C++20)	obtains the result type of the three-way comparison operator <=> on given types (class template)
compare_three_way (C++20)	function object implementing x <=> y (class)
Customization point objects
strong_order (C++20)	performs 3-way comparison and produces a result of type std::strong_ordering (customization point object)
weak_order (C++20)	performs 3-way comparison and produces a result of type std::weak_ordering (customization point object)
partial_order (C++20)	performs 3-way comparison and produces a result of type std::partial_ordering (customization point object)
compare_strong_order_fallback (C++20)	performs 3-way comparison and produces a result of type std::strong_ordering, even if operator<=> is unavailable (customization point object)
compare_weak_order_fallback (C++20)	performs 3-way comparison and produces a result of type std::weak_ordering, even if operator<=> is unavailable (customization point object)
compare_partial_order_fallback (C++20)	performs 3-way comparison and produces a result of type std::partial_ordering, even if operator<=> is unavailable (customization point object)
Functions
is_eqis_neqis_ltis_lteqis_gtis_gteq (C++20)	named comparison functions (function)

Synopsis

namespace std {// comparison category typesclass partial_ordering;class weak_ordering;class strong_ordering;   // named comparison functionsconstexprbool is_eq (partial_ordering cmp)noexcept{return cmp ==0;}constexprbool is_neq (partial_ordering cmp)noexcept{return cmp !=0;}constexprbool is_lt (partial_ordering cmp)noexcept{return cmp <0;}constexprbool is_lteq(partial_ordering cmp)noexcept{return cmp <=0;}constexprbool is_gt (partial_ordering cmp)noexcept{return cmp >0;}constexprbool is_gteq(partial_ordering cmp)noexcept{return cmp >=0;}   // common comparison category typetemplate<class... Ts>struct common_comparison_category {using type =/* see description */;};template<class... Ts>using common_comparison_category_t =typename common_comparison_category<Ts...>::type;   // concept three_way_comparabletemplate<class T, class Cat = partial_ordering> concept three_way_comparable =/* see description */;template<class T, class U, class Cat = partial_ordering> concept three_way_comparable_with =/* see description */;   // result of three-way comparisontemplate<class T, class U = T>struct compare_three_way_result;   template<class T, class U = T>using compare_three_way_result_t =typename compare_three_way_result<T, U>::type;   // class compare_three_waystruct compare_three_way;   // comparison algorithmsinlinenamespace/* unspecified */{inlineconstexpr/* unspecified */ strong_order =/* unspecified */;inlineconstexpr/* unspecified */ weak_order =/* unspecified */;inlineconstexpr/* unspecified */ partial_order =/* unspecified */;inlineconstexpr/* unspecified */ compare_strong_order_fallback =/* unspecified */;inlineconstexpr/* unspecified */ compare_weak_order_fallback =/* unspecified */;inlineconstexpr/* unspecified */ compare_partial_order_fallback =/* unspecified */;}}

Concept three_way_comparable

namespace std {template<class T, class Cat> concept __ComparesAs =// exposition only same_as<common_comparison_category_t<T, Cat>, Cat>;   template<class T, class U> concept __PartiallyOrderedWith =// exposition only requires(const remove_reference_t<T>& t, const remove_reference_t<U>& u){{ t < u }->boolean-testable;{ t > u }->boolean-testable;{ t <= u }->boolean-testable;{ t >= u }->boolean-testable;{ u < t }->boolean-testable;{ u > t }->boolean-testable;{ u <= t }->boolean-testable;{ u >= t }->boolean-testable;};   template<class T, class Cat = partial_ordering> concept three_way_comparable = __WeaklyEqualityComparableWith<T, T>&& __PartiallyOrderedWith<T, T>&& requires(const remove_reference_t<T>& a, const remove_reference_t<T>& b){{ a <=> b }-> __ComparesAs<Cat>;};}

Concept three_way_comparable_with

namespace std {template<class T, class U, class Cat = partial_ordering> concept three_way_comparable_with = __WeaklyEqualityComparableWith<T, U>&& __PartiallyOrderedWith<T, U>&& three_way_comparable<T, Cat>&& three_way_comparable<U, Cat>&& common_reference_with<const remove_reference_t<T>&, const remove_reference_t<U>&>&& three_way_comparable< common_reference_t<const remove_reference_t<T>&, const remove_reference_t<U>&>, Cat>&& requires(const remove_reference_t<T>& t, const remove_reference_t<U>& u){{ t <=> u }-> __ComparesAs<Cat>;{ u <=> t }-> __ComparesAs<Cat>;};}

Class std::partial_ordering

namespace std {class partial_ordering {int value;// exposition onlybool is_ordered;// exposition only   // exposition-only constructorsconstexprexplicit partial_ordering(eq v)noexcept: value(int(v)), is_ordered(true){}// exposition onlyconstexprexplicit partial_ordering(ord v)noexcept: value(int(v)), is_ordered(true){}// exposition onlyconstexprexplicit partial_ordering(ncmp v)noexcept: value(int(v)), is_ordered(false){}// exposition only   public:// valid valuesstaticconst partial_ordering less;staticconst partial_ordering equivalent;staticconst partial_ordering greater;staticconst partial_ordering unordered;   // comparisonsfriendconstexprbool operator==(partial_ordering v, /* unspecified */)noexcept;friendconstexprbool operator==(partial_ordering v, partial_ordering w)noexcept=default;friendconstexprbool operator<(partial_ordering v, /* unspecified */)noexcept;friendconstexprbool operator>(partial_ordering v, /* unspecified */)noexcept;friendconstexprbool operator<=(partial_ordering v, /* unspecified */)noexcept;friendconstexprbool operator>=(partial_ordering v, /* unspecified */)noexcept;friendconstexprbool operator<(/* unspecified */, partial_ordering v)noexcept;friendconstexprbool operator>(/* unspecified */, partial_ordering v)noexcept;friendconstexprbool operator<=(/* unspecified */, partial_ordering v)noexcept;friendconstexprbool operator>=(/* unspecified */, partial_ordering v)noexcept;friendconstexpr partial_ordering operator<=>(partial_ordering v, /* unspecified */)noexcept;friendconstexpr partial_ordering operator<=>(/* unspecified */, partial_ordering v)noexcept;};   // valid values' definitionsinlineconstexpr partial_ordering partial_ordering::less(ord::less);inlineconstexpr partial_ordering partial_ordering::equivalent(eq::equivalent);inlineconstexpr partial_ordering partial_ordering::greater(ord::greater);inlineconstexpr partial_ordering partial_ordering::unordered(ncmp::unordered);}

Class std::weak_ordering

namespace std {class weak_ordering {int value;// exposition only   // exposition-only constructorsconstexprexplicit weak_ordering(eq v)noexcept: value(int(v)){}// exposition onlyconstexprexplicit weak_ordering(ord v)noexcept: value(int(v)){}// exposition only   public:// valid valuesstaticconst weak_ordering less;staticconst weak_ordering equivalent;staticconst weak_ordering greater;   // conversionsconstexpr operator partial_ordering()constnoexcept;   // comparisonsfriendconstexprbool operator==(weak_ordering v, /* unspecified */)noexcept;friendconstexprbool operator==(weak_ordering v, weak_ordering w)noexcept=default;friendconstexprbool operator<(weak_ordering v, /* unspecified */)noexcept;friendconstexprbool operator>(weak_ordering v, /* unspecified */)noexcept;friendconstexprbool operator<=(weak_ordering v, /* unspecified */)noexcept;friendconstexprbool operator>=(weak_ordering v, /* unspecified */)noexcept;friendconstexprbool operator<(/* unspecified */, weak_ordering v)noexcept;friendconstexprbool operator>(/* unspecified */, weak_ordering v)noexcept;friendconstexprbool operator<=(/* unspecified */, weak_ordering v)noexcept;friendconstexprbool operator>=(/* unspecified */, weak_ordering v)noexcept;friendconstexpr weak_ordering operator<=>(weak_ordering v, /* unspecified */)noexcept;friendconstexpr weak_ordering operator<=>(/* unspecified */, weak_ordering v)noexcept;};   // valid values' definitionsinlineconstexpr weak_ordering weak_ordering::less(ord::less);inlineconstexpr weak_ordering weak_ordering::equivalent(eq::equivalent);inlineconstexpr weak_ordering weak_ordering::greater(ord::greater);}

Class std::strong_ordering

namespace std {class strong_ordering {int value;// exposition only   // exposition-only constructorsconstexprexplicit strong_ordering(eq v)noexcept: value(int(v)){}// exposition onlyconstexprexplicit strong_ordering(ord v)noexcept: value(int(v)){}// exposition only   public:// valid valuesstaticconst strong_ordering less;staticconst strong_ordering equal;staticconst strong_ordering equivalent;staticconst strong_ordering greater;   // conversionsconstexpr operator partial_ordering()constnoexcept;constexpr operator weak_ordering()constnoexcept;   // comparisonsfriendconstexprbool operator==(strong_ordering v, /* unspecified */)noexcept;friendconstexprbool operator==(strong_ordering v, strong_ordering w)noexcept=default;friendconstexprbool operator<(strong_ordering v, /* unspecified */)noexcept;friendconstexprbool operator>(strong_ordering v, /* unspecified */)noexcept;friendconstexprbool operator<=(strong_ordering v, /* unspecified */)noexcept;friendconstexprbool operator>=(strong_ordering v, /* unspecified */)noexcept;friendconstexprbool operator<(/* unspecified */, strong_ordering v)noexcept;friendconstexprbool operator>(/* unspecified */, strong_ordering v)noexcept;friendconstexprbool operator<=(/* unspecified */, strong_ordering v)noexcept;friendconstexprbool operator>=(/* unspecified */, strong_ordering v)noexcept;friendconstexpr strong_ordering operator<=>(strong_ordering v, /* unspecified */)noexcept;friendconstexpr strong_ordering operator<=>(/* unspecified */, strong_ordering v)noexcept;};   // valid values' definitionsinlineconstexpr strong_ordering strong_ordering::less(ord::less);inlineconstexpr strong_ordering strong_ordering::equal(eq::equal);inlineconstexpr strong_ordering strong_ordering::equivalent(eq::equivalent);inlineconstexpr strong_ordering strong_ordering::greater(ord::greater);}

Class std::compare_three_way

namespace std {struct compare_three_way {template<class T, class U> requires three_way_comparable_with<T, U>||/*BUILTIN-PTR-THREE-WAY*/(T, U)constexprauto operator()(T&& t, U&& u)const;   using is_transparent =/* unspecified */;};}

See also

C++ documentation for three-way comparison operator (C++20)