std::strong_ordering (3) - Linux Manuals
std::strong_ordering: std::strong_ordering
NAME
std::strong_ordering - std::strong_ordering
Synopsis
Defined in header <compare>
class strong_ordering; (since C++20)
The class type std::strong_ordering is the result type of a three-way_comparison that
* admits all six relational operators (==, !=, <, <=, >, >=)
* implies substitutability: if a is equivalent to b, f(a) is also 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 are indistinguishable.
* does not allow incomparable values: at least one of a < b, a == b, and a > b must be true
Constants
The type std::strong_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::strong_ordering indicating less-than (ordered before) relationship
[static]
equivalent(inline constexpr) a valid value of the type std::strong_ordering indicating equivalence (neither ordered before nor ordered after)
[static]
equal(inline constexpr) a valid value of the type std::strong_ordering indicating equivalence (neither ordered before nor ordered after)
[static]
greater(inline constexpr) a valid value of the type std::strong_ordering indicating greater-than (ordered after) relationship
[static]
Conversions
std::strong_ordering is the strongest of the five comparison categories: it is not implicitly-convertible from any other category and is implicitly-convertible to the other four.
operator strong_equality (public member function)
std::strong_ordering::operator strong_equality
constexpr operator strong_equality() const noexcept;
Return value
std::strong_equality::equal if v is equivalent or equal, std::strong_equality::nonequal if v is less or greater.
operator weak_equality (public member function)
std::strong_ordering::operator weak_equality
constexpr operator weak_equality() const noexcept;
Return value
std::weak_equality::equivalent if v is equal or equivalent, std::weak_equality::nonequivalent if v is less or greater.
operator partial_ordering (public member function)
std::strong_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 equal or equivalent.
operator weak_ordering (public member function)
std::strong_ordering::operator weak_ordering
constexpr operator weak_ordering() const noexcept;
Return value
std::weak_ordering::less if v is less, std::weak_ordering::greater if v is greater, std::weak_ordering::equivalent if v is equal or 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.
The behavior of a program that attempts to compare a strong_ordering with anything other than the integer literal 0 is undefined.
operator==
operator!=
operator< compares with zero
operator> (function)
operator<=
operator>=
operator<=>
operator==
friend constexpr bool operator==(strong_ordering v, /*unspecified*/ u) noexcept;
friend constexpr bool operator==(/*unspecified*/ u, strong_ordering v) noexcept;
Parameters
v - a std::strong_ordering value to check
u - an unused parameter of any type that accepts literal zero argument
Return value
true if v is equivalent or equal, false if v is less or greater
operator!=
friend constexpr bool operator!=(strong_ordering v, /*unspecified*/ u) noexcept;
friend constexpr bool operator!=(/*unspecified*/ u, strong_ordering v) noexcept;
Parameters
v - a std::strong_ordering value to check
u - an unused parameter of any type that accepts literal zero argument
Return value
true if v is less or greater, and false if v is equivalent or equal
operator<
friend constexpr bool operator<(strong_ordering v, /*unspecified*/ u) noexcept; (1)
friend constexpr bool operator<(/*unspecified*/ u, strong_ordering v) noexcept; (2)
Parameters
v - a std::strong_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 equal
2) true if v is greater, and false if v is less, equivalent, or equal
operator<=
friend constexpr bool operator<=(strong_ordering v, /*unspecified*/ u) noexcept; (1)
friend constexpr bool operator<=(/*unspecified*/ u, strong_ordering v) noexcept; (2)
Parameters
v - a std::strong_ordering value to check
u - an unused parameter of any type that accepts literal zero argument
Return value
1) true if v is less, equivalent, or equal, and false if v is greater
2) true if v is greater, equivalent, or equal, and false if v is less
operator>
friend constexpr bool operator>(strong_ordering v, /*unspecified*/ u) noexcept; (1)
friend constexpr bool operator>(/*unspecified*/ u, strong_ordering v) noexcept; (2)
Parameters
v - a std::strong_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 equal
2) true if v is less, and false if v is greater, equivalent, or equal
operator>=
friend constexpr bool operator>=(strong_ordering v, /*unspecified*/ u) noexcept; (1)
friend constexpr bool operator>=(/*unspecified*/ u, strong_ordering v) noexcept; (2)
Parameters
v - a std::strong_ordering value to check
u - an unused parameter of any type that accepts literal zero argument
Return value
1) true if v is greater, equivalent, or equal, and false if v is less
2) true if v is less, equivalent, or equal, and false if v is greater
operator<=>
friend constexpr strong_ordering operator<=>(strong_ordering v, /*unspecified*/ u) noexcept; (1)
friend constexpr strong_ordering operator<=>(/*unspecified*/ u, strong_ordering v) noexcept; (2)
Parameters
v - a std::strong_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
weak_ordering the result type of 3-way comparison that supports all 6 operators and is not substitutable
(C++20)
partial_ordering the result type of 3-way comparison that supports all 6 operators, is not substitutable, and allows incomparable values
(C++20)
strong_equality the result type of 3-way comparison that supports only equality/inequality and is substitutable