std::partial_ordering(3) C++ Standard Libary std::partial_ordering(3) NAME std::partial_ordering - std::partial_ordering Synopsis Defined in header <compare> class partial_ordering; (since C++20) The class type std::partial_ordering is the result type of a three-way comparison that: * Admits all six relational operators (==, !=, <, <=, >, >=). * Does not imply substitutability: if a is equivalent to b, f(a) may not be equivalent to f(b), where f denotes a function that reads only comparison-salient state that is accessible via the argument's pub- lic const members. In other words, equivalent values may be distinguishable. * Admits incomparable values: a < b, a == b, and a > b may all be false. Constants The type std::partial_ordering has four valid values, implemented as const static data members of its type: Member constant Definition less(inline constexpr) a valid value of the type std::partial_or- dering [static] indicating less-than (ordered before) rela- tionship (public static member constant) a valid value of the type std::partial_or- dering equivalent(inline constexpr) indicating equivalence (neither ordered be- fore nor [static] ordered after) (public static member constant) greater(inline constexpr) a valid value of the type std::partial_or- dering [static] indicating greater-than (ordered after) re- lationship (public static member constant) unordered(inline constexpr) a valid value of the type std::partial_or- dering [static] indicating relationship with an incompara- ble value (public static member constant) Conversions std::partial_ordering cannot be implicitly converted to other comparison category types, while both std::strong_ordering and std::weak_ordering are implicitly-convertible to partial_ordering. Comparisons Comparison operators are defined between values of this type and literal 0. This supports the expressions a <=> b == 0 or a <=> b < 0 that can be used to convert the result of a three-way comparison operator to a boolean relationship; see std::is_eq, std::is_lt, etc. These functions are not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when std::partial_ordering is an associated class of the arguments. The behavior of a program that attempts to compare a partial_ordering with anything other than the integer literal 0 is undefined. operator== operator< operator> compares with zero or a partial_ordering operator<= (function) operator>= operator<=> operator== friend constexpr bool operator==( partial_ordering v, /*unspecified*/ u ) (1) noexcept; friend constexpr bool (2) operator==( partial_ordering v, partial_ordering w ) noexcept = de- fault; Parameters v, w - std::partial_ordering values to check u - an unused parameter of any type that accepts literal zero argu- ment Return value 1) true if v is equivalent, false if v is less, greater, or unordered 2) true if both parameters hold the same value, false otherwise operator< friend constexpr bool operator<( partial_ordering v, /*unspecified*/ u ) (1) noexcept; friend constexpr bool operator<( /*unspecified*/ u, partial_ordering v ) (2) noexcept; Parameters v - a std::partial_ordering value to check u - an unused parameter of any type that accepts literal zero argument Return value 1) true if v is less, and false if v is greater, equivalent, or un- ordered 2) true if v is greater, and false if v is less, equivalent, or un- ordered operator<= friend constexpr bool operator<=( partial_ordering v, /*unspecified*/ u ) (1) noexcept; friend constexpr bool operator<=( /*unspecified*/ u, partial_ordering v ) (2) noexcept; Parameters v - a std::partial_ordering value to check u - an unused parameter of any type that accepts literal zero argument Return value 1) true if v is less or equivalent, and false if v is greater or un- ordered 2) true if v is greater or equivalent, and false if v is less or un- ordered operator> friend constexpr bool operator>( partial_ordering v, /*unspecified*/ u ) (1) noexcept; friend constexpr bool operator>( /*unspecified*/ u, partial_ordering v ) (2) noexcept; Parameters v - a std::partial_ordering value to check u - an unused parameter of any type that accepts literal zero argument Return value 1) true if v is greater, and false if v is less, equivalent, or un- ordered 2) true if v is less, and false if v is greater, equivalent, or un- ordered operator>= friend constexpr bool operator>=( partial_ordering v, /*unspecified*/ u ) (1) noexcept; friend constexpr bool operator>=( /*unspecified*/ u, partial_ordering v ) (2) noexcept; Parameters v - a std::partial_ordering value to check u - an unused parameter of any type that accepts literal zero argument Return value 1) true if v is greater or equivalent, and false if v is less or un- ordered 2) true if v is less or equivalent, and false if v is greater or un- ordered operator<=> friend constexpr partial_ordering operator<=>( partial_ordering v, (1) /*unspecified*/ u ) noexcept; friend constexpr partial_ordering operator<=>( /*unspecified*/ u, (2) partial_ordering v ) noexcept; Parameters v - a std::partial_ordering value to check u - an unused parameter of any type that accepts literal zero argument Return value 1) v. 2) greater if v is less, less if v is greater, otherwise v. Notes The built-in operator<=> between floating-point values uses this order- ing: the positive zero and the negative zero compare equivalent, but can be dis- tinguished, and NaN values compare unordered with any other value. Example This section is incomplete Reason: no example See also strong_ordering the result type of 3-way comparison that supports all 6 operators (C++20) and is substitutable (class) weak_ordering the result type of 3-way comparison that supports all 6 operators (C++20) and is not substitutable (class) Category: * Todo no example http://cppreference.com 2024.06.10 std::partial_ordering(3)
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