std::strong_ordering
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)
[static] | a valid value of the type std::strong_ordering indicating less-than (ordered before) relationship (public static member constant) |
| equivalent(inline constexpr)
[static] | a valid value of the type std::strong_ordering indicating equivalence (neither ordered before nor ordered after) (public static member constant) |
| equal(inline constexpr)
[static] | a valid value of the type std::strong_ordering indicating equivalence (neither ordered before nor ordered after) (public static member constant) |
| greater(inline constexpr)
[static] | a valid value of the type std::strong_ordering indicating greater-than (ordered after) relationship (public static member constant) |
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 | implicit conversion to std::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 | implicit conversion to std::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 | implicit conversion to std::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 | implicit conversion to std::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<operator>operator<=operator>=operator<=> | compares with zero (function) |
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
true if v is less, and false if v is greater, equivalent, or equal
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
true if v is less, equivalent, or equal, and false if v is greater
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
true if v is greater, and false if v is less, equivalent, or equal
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
true if v is greater, equivalent, or equal, and false if v is less
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
v.greater if v is less, less if v is greater, otherwise v. Example
See also
|
(C++20) | the result type of 3-way comparison that supports all 6 operators and is not substitutable (class) |
|
(C++20) | the result type of 3-way comparison that supports all 6 operators, is not substitutable, and allows incomparable values (class) |
|
(C++20) | the result type of 3-way comparison that supports only equality/inequality and is substitutable (class) |
|
(C++20) | the result type of 3-way comparison that supports only equality/inequality and is not substitutable (class) |
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