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std::weak_ordering(3) C++ Standard Libary std::weak_ordering(3) NAME std::weak_ordering - std::weak_ordering Synopsis Defined in header <compare> class weak_ordering; (since C++20) The class type std::weak_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 public const members. In other words, equivalent values may be distinguish- able. * does not allow incomparable values: exactly one of a < b, a == b, or a > b must be true Constants The type std::weak_ordering has three valid values, implemented as const static data members of its type: Member constant Definition less(inline constexpr) a valid value of the type std::weak_or- dering indicating [static] less-than (ordered before) relationship (public static member constant) equivalent(inline constexpr) a valid value of the type std::weak_or- dering indicating [static] equivalence (neither ordered before nor ordered after) (public static member constant) greater(inline constexpr) a valid value of the type std::weak_or- dering indicating [static] greater-than (ordered after) relation- ship (public static member constant) Conversions std::weak_ordering is implicitly-convertible to std::partial_order- ing, while std::strong_ordering is implicitly-convertible to weak_ordering. operator partial_ordering implicit conversion to std::partial_order- ing (public member function) std::weak_ordering::operator partial_ordering constexpr operator partial_ordering() const noexcept; Return value std::partial_ordering::less if v is less, std::partial_order- ing::greater if v is greater, std::partial_ordering::equivalent if v is equivalent. 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::weak_ordering is an associated class of the arguments. The behavior of a program that attempts to compare a weak_ordering with anything other than the integer literal 0 is undefined. operator== operator< operator> compares with zero or a weak_ordering operator<= (function) operator>= operator<=> operator== friend constexpr bool operator==(weak_ordering v, /*unspecified*/ u) noexcept; (1) friend constexpr bool operator==(weak_ordering v, weak_ordering w) noexcept = (2) default; Parameters v, w - std::weak_ordering values to check u - an unused parameter of any type that accepts literal zero ar- gument Return value 1) true if v is equivalent, false if v is less or greater 2) true if both parameters hold the same value, false otherwise operator< friend constexpr bool operator<(weak_ordering v, /*unspecified*/ u) noexcept; (1) friend constexpr bool operator<(/*unspecified*/ u, weak_ordering v) noexcept; (2) Parameters v - a std::weak_ordering value to check u - an unused parameter of any type that accepts literal zero argu- ment Return value 1) true if v is less, and false if v is greater or equivalent 2) true if v is greater, and false if v is less or equivalent operator<= friend constexpr bool operator<=(weak_ordering v, /*unspecified*/ u) noexcept; (1) friend constexpr bool operator<=(/*unspecified*/ u, weak_ordering v) noexcept; (2) Parameters v - a std::weak_ordering value to check u - an unused parameter of any type that accepts literal zero argu- ment Return value 1) true if v is less or equivalent, and false if v is greater 2) true if v is greater or equivalent, and false if v is less operator> friend constexpr bool operator>(weak_ordering v, /*unspecified*/ u) noexcept; (1) friend constexpr bool operator>(/*unspecified*/ u, weak_ordering v) noexcept; (2) Parameters v - a std::weak_ordering value to check u - an unused parameter of any type that accepts literal zero argu- ment Return value 1) true if v is greater, and false if v is less or equivalent 2) true if v is less, and false if v is greater or equivalent operator>= friend constexpr bool operator>=(weak_ordering v, /*unspecified*/ u) noexcept; (1) friend constexpr bool operator>=(/*unspecified*/ u, weak_ordering v) noexcept; (2) Parameters v - a std::weak_ordering value to check u - an unused parameter of any type that accepts literal zero argu- ment Return value 1) true if v is greater or equivalent, and false if v is less 2) true if v is less or equivalent, and false if v is greater operator<=> friend constexpr weak_ordering operator<=>(weak_ordering v, /*un- specified*/ u) (1) noexcept; friend constexpr weak_ordering operator<=>(/*unspecified*/ u, weak_ordering v) (2) noexcept; Parameters v - a std::weak_ordering value to check u - an unused parameter of any type that accepts literal zero argu- ment Return value 1) v. 2) greater if v is less, less if v is greater, otherwise v. 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) partial_ordering the result type of 3-way comparison that supports all 6 operators, (C++20) is not substitutable, and allows incomparable val- ues (class) http://cppreference.com 2022.07.31 std::weak_ordering(3)
NAME | Synopsis | Constants | Conversions | Return value | Comparisons | Parameters | Return value | Parameters | Return value | Parameters | Return value | Parameters | Return value | Parameters | Return value | Parameters | Return value | Example | See also
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