Standard library header <compare>

C++

Language

Headers

Freestanding and hosted implementations

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.

Classes

weak_equality (C++20)	the result type of 3-way comparison that supports only equality/inequality and is not substitutable (class)
strong_equality (C++20)	the result type of 3-way comparison that supports only equality/inequality and is substitutable (class)
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)

Functions

is_eqis_neqis_ltis_lteqis_gtis_gteq (C++20)	named comparison functions (function)
strong_order (C++20)	performs 3-way comparison and produces a result of type std::strong_ordering (function template)
weak_order (C++20)	performs 3-way comparison and produces a result of type std::weak_ordering (function template)
partial_order (C++20)	performs 3-way comparison and produces a result of type std::partial_ordering (function template)
strong_equal (C++20)	performs 3-way comparison and produces a result of type std::strong_equality (function template)
weak_equal (C++20)	performs 3-way comparison and produces a result of type std::weak_equality (function template)

Synopsis

namespace std {
  // comparison category types
  class weak_equality;
  class strong_equality;
  class partial_ordering;
  class weak_ordering;
  class strong_ordering;
  // named comparison functions
  constexpr bool is_eq (weak_equality cmp) noexcept { return cmp == 0; }
  constexpr bool is_neq (weak_equality cmp) noexcept { return cmp != 0; }
  constexpr bool is_lt (partial_ordering cmp) noexcept { return cmp < 0; }
  constexpr bool is_lteq(partial_ordering cmp) noexcept { return cmp <= 0; }
  constexpr bool is_gt (partial_ordering cmp) noexcept { return cmp > 0; }
  constexpr bool is_gteq(partial_ordering cmp) noexcept { return cmp >= 0; }
  // common comparison category type
  template<class... Ts>
  struct common_comparison_category {
    using type = /* see definition */ ;
  };
  template<class... Ts>
  using common_comparison_category_t = typename common_comparison_category<Ts...>::type;
  // comparison algorithms
  template<class T> constexpr strong_ordering strong_order(const T& a, const T& b);
  template<class T> constexpr weak_ordering weak_order(const T& a, const T& b);
  template<class T> constexpr partial_ordering partial_order(const T& a, const T& b);
  template<class T> constexpr strong_equality strong_equal(const T& a, const T& b);
  template<class T> constexpr weak_equality weak_equal(const T& a, const T& b);
}

Class std::weak_equality

namespace std {
  class weak_equality {
    int value; // exposition only
    // exposition-only constructor
    explicit constexpr weak_equality(eq v) noexcept : value(int(v)) {} // exposition only
    public:
    // valid values
    static const weak_equality equivalent;
    static const weak_equality nonequivalent;
    // comparisons
    friend constexpr bool operator==(weak_equality v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator!=(weak_equality v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator==(/*unspecified*/ , weak_equality v) noexcept;
    friend constexpr bool operator!=(/*unspecified*/ , weak_equality v) noexcept;
  };
  // valid values definitions
  inline constexpr weak_equality weak_equality::equivalent(eq::equivalent);
  inline constexpr weak_equality weak_equality::nonequivalent(eq::nonequivalent);
}

Class std::strong_equality

namespace std {
  class strong_equality {
    int value; // exposition only
    // exposition-only constructor
    explicit constexpr strong_equality(eq v) noexcept : value(int(v)) {} // exposition only
    public:
    // valid values
    static const strong_equality equal;
    static const strong_equality nonequal;
    static const strong_equality equivalent;
    static const strong_equality nonequivalent;
    // conversion
    constexpr operator weak_equality() const noexcept;
    // comparisons
    friend constexpr bool operator==(strong_equality v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator!=(strong_equality v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator==(/*unspecified*/ , strong_equality v) noexcept;
    friend constexpr bool operator!=(/*unspecified*/ , strong_equality v) noexcept;
  };
  // valid values definitions
  inline constexpr strong_equality strong_equality::equal(eq::equal);
  inline constexpr strong_equality strong_equality::nonequal(eq::nonequal);
  inline constexpr strong_equality strong_equality::equivalent(eq::equivalent);
  inline constexpr strong_equality strong_equality::nonequivalent(eq::nonequivalent);
}

Class std::partial_ordering

namespace std {
  class partial_ordering {
    int value; // exposition only
    bool is_ordered; // exposition only
    // exposition-only constructors
    explicit constexpr
    partial_ordering(eq v) noexcept : value(int(v)), is_ordered(true) {} // exposition only
    explicit constexpr
    partial_ordering(ord v) noexcept : value(int(v)), is_ordered(true) {} // exposition only
    explicit constexpr
    partial_ordering(ncmp v) noexcept : value(int(v)), is_ordered(false) {} // exposition only
    public:
    // valid values
    static const partial_ordering less;
    static const partial_ordering equivalent;
    static const partial_ordering greater;
    static const partial_ordering unordered;
    // conversion
    constexpr operator weak_equality() const noexcept;
    // comparisons
    friend constexpr bool operator==(partial_ordering v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator!=(partial_ordering v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator< (partial_ordering v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator<=(partial_ordering v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator> (partial_ordering v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator>=(partial_ordering v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator==(/*unspecified*/ , partial_ordering v) noexcept;
    friend constexpr bool operator!=(/*unspecified*/ , partial_ordering v) noexcept;
    friend constexpr bool operator< (/*unspecified*/ , partial_ordering v) noexcept;
    friend constexpr bool operator<=(/*unspecified*/ , partial_ordering v) noexcept;
    friend constexpr bool operator> (/*unspecified*/ , partial_ordering v) noexcept;
    friend constexpr bool operator>=(/*unspecified*/ , partial_ordering v) noexcept;
  };
  // valid values definitions
  inline constexpr partial_ordering partial_ordering::less(ord::less);
  inline constexpr partial_ordering partial_ordering::equivalent(eq::equivalent);
  inline constexpr partial_ordering partial_ordering::greater(ord::greater);
  inline constexpr partial_ordering partial_ordering::unordered(ncmp::unordered);
}

Class std::weak_ordering

namespace std {
  class weak_ordering {
    int value; // exposition only
    // exposition-only constructors
    explicit constexpr weak_ordering(eq v) noexcept : value(int(v)) {} // exposition only
    explicit constexpr weak_ordering(ord v) noexcept : value(int(v)) {} // exposition only
    public:
    // valid values
    static const weak_ordering less;
    static const weak_ordering equivalent;
    static const weak_ordering greater;
    // conversions
    constexpr operator weak_equality() const noexcept;
    constexpr operator partial_ordering() const noexcept;
    // comparisons
    friend constexpr bool operator==(weak_ordering v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator!=(weak_ordering v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator< (weak_ordering v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator<=(weak_ordering v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator> (weak_ordering v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator>=(weak_ordering v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator==(/*unspecified*/ , weak_ordering v) noexcept;
    friend constexpr bool operator!=(/*unspecified*/ , weak_ordering v) noexcept;
    friend constexpr bool operator< (/*unspecified*/ , weak_ordering v) noexcept;
    friend constexpr bool operator<=(/*unspecified*/ , weak_ordering v) noexcept;
    friend constexpr bool operator> (/*unspecified*/ , weak_ordering v) noexcept;
    friend constexpr bool operator>=(/*unspecified*/ , weak_ordering v) noexcept;
  };
  // valid values definitions
  inline constexpr weak_ordering weak_ordering::less(ord::less);
  inline constexpr weak_ordering weak_ordering::equivalent(eq::equivalent);
  inline constexpr weak_ordering weak_ordering::greater(ord::greater);
}

Class std::strong_ordering

namespace std {
  class strong_ordering {
    int value; // exposition only
    // exposition-only constructors
    explicit constexpr strong_ordering(eq v) noexcept : value(int(v)) {} // exposition only
    explicit constexpr strong_ordering(ord v) noexcept : value(int(v)) {} // exposition only
    public:
    // valid values
    static const strong_ordering less;
    static const strong_ordering equal;
    static const strong_ordering equivalent;
    static const strong_ordering greater;
    // conversions
    constexpr operator weak_equality() const noexcept;
    constexpr operator strong_equality() const noexcept;
    constexpr operator partial_ordering() const noexcept;
    constexpr operator weak_ordering() const noexcept;
    // comparisons
    friend constexpr bool operator==(strong_ordering v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator!=(strong_ordering v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator< (strong_ordering v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator<=(strong_ordering v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator> (strong_ordering v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator>=(strong_ordering v, /*unspecified*/ ) noexcept;
    friend constexpr bool operator==(/*unspecified*/ , strong_ordering v) noexcept;
    friend constexpr bool operator!=(/*unspecified*/ , strong_ordering v) noexcept;
    friend constexpr bool operator< (/*unspecified*/ , strong_ordering v) noexcept;
    friend constexpr bool operator<=(/*unspecified*/ , strong_ordering v) noexcept;
    friend constexpr bool operator> (/*unspecified*/ , strong_ordering v) noexcept;
    friend constexpr bool operator>=(/*unspecified*/ , strong_ordering v) noexcept;
  };
  // valid values definitions
  inline constexpr strong_ordering strong_ordering::less(ord::less);
  inline constexpr strong_ordering strong_ordering::equal(eq::equal);
  inline constexpr strong_ordering strong_ordering::equivalent(eq::equivalent);
  inline constexpr strong_ordering strong_ordering::greater(ord::greater);
}