std:: weak_ordering

From cppreference.com
C++
Utilities library
General utilities
Relational operators (deprecated in C++20)
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 distinguishable.
  • 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:

Name Definition
inline constexpr std :: weak_ordering less
[static]
a valid value indicating less-than (ordered before) relationship
(public static member constant)
inline constexpr std :: weak_ordering equivalent
[static]
a valid value indicating equivalence (neither ordered before nor ordered after)
(public static member constant)
inline constexpr std :: weak_ordering greater
[static]
a valid value indicating greater-than (ordered after) relationship
(public static member constant)

Conversions

std::weak_ordering is implicitly-convertible to std::partial_ordering , while std::strong_ordering is implicitly-convertible to weak_ordering .

operator partial_ordering
implicit conversion to std::partial_ordering
(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_ordering::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> operator<= operator>= operator<=>
compares with zero or a weak_ordering
(function)

operator==

friend constexpr bool operator == ( weak_ordering v, /*unspecified*/ u ) noexcept ;
(1)
friend constexpr bool operator == ( weak_ordering v, weak_ordering w ) noexcept = default ;
(2)

Parameters

v, w - std::weak_ordering values to check
u - an unused parameter of any type that accepts literal zero argument

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 argument

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 argument

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 argument

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 argument

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, /*unspecified*/ u ) noexcept ;
(1)
friend constexpr weak_ordering 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 argument

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

(C++20)
the result type of 3-way comparison that supports all 6 operators and is substitutable
(class)
(C++20)
the result type of 3-way comparison that supports all 6 operators, is not substitutable, and allows incomparable values
(class)
Retrieved from " https://en.cppreference.com/mwiki/index.php?title=cpp/utility/compare/weak_ordering&oldid=173502 "