Defined in header <compare> | ||
---|---|---|
inline namespace /* unspecified */ { inline constexpr /* unspecified */ strong_order = /* unspecified */; } | (since C++20) | |
Call signature | ||
template< class T, class U > requires /* see below */ constexpr std::strong_ordering strong_order( T&& t, U&& u ) noexcept(/* see below */); |
Compares two values using 3-way comparison and produces a result of type std::strong_ordering
.
Let t
and u
be expressions and T
and U
denote decltype((t))
and decltype((u))
respectively, std::strong_order(t, u)
is expression-equivalent to:
std::is_same_v<std::decay_t<T>, std::decay_t<U>>
is true
: std::strong_ordering(strong_order(t, u))
, if it is a well-formed expression with overload resolution performed in a context that does not include a declaration of std::strong_order
, T
is a floating-point type: std::numeric_limits<T>::is_iec559
is true
, performs the ISO/IEC/IEEE 60559 totalOrder comparison of floating-point values and returns that result as a value of type std::strong_ordering
(note: this comparison can distinguish between the positive and negative zero and between the NaNs with different representations), std::strong_ordering
that is consistent with the ordering observed by T
's comparison operators, std::strong_ordering(std::compare_three_way()(t, u))
if it is well-formed. The name std::strong_order
denotes a customization point object, which is a const function object of a literal semiregular
class type. For exposition purposes, the cv-unqualified version of its type is denoted as __strong_order_fn
.
All instances of __strong_order_fn
are equal. The effects of invoking different instances of type __strong_order_fn
on the same arguments are equivalent, regardless of whether the expression denoting the instance is an lvalue or rvalue, and is const-qualified or not (however, a volatile-qualified instance is not required to be invocable). Thus, std::strong_order
can be copied freely and its copies can be used interchangeably.
Given a set of types Args...
, if std::declval<Args>()...
meet the requirements for arguments to std::strong_order
above, __strong_order_fn
models
.
std::invocable<__strong_order_fn, Args...>
, std::invocable<const __strong_order_fn, Args...>
, std::invocable<__strong_order_fn&, Args...>
, and std::invocable<const __strong_order_fn&, Args...>
.Otherwise, no function call operator of __strong_order_fn
participates in overload resolution.
Let x
and y
be values of same IEEE floating-point type, and total_order_less(x, y)
be the boolean result indicating if x
precedes y
in the strict total order defined by totalOrder in ISO/IEC/IEEE 60559.
(total_order_less(x, y) || total_order_less(y, x)) == false
if and only if x
and y
have the same bit pattern.
x
nor y
is NaN: x < y
, then total_order_less(x, y) == true
; x > y
, then total_order_less(x, y) == false
; x == y
, x
is negative zero and y
is positive zero, total_order_less(x, y) == true
, x
is not zero and x
's exponent field is less than y
's, then total_order_less(x, y) == (x > 0)
(only meaningful for decimal floating-point number); x
or y
is NaN: x
is negative NaN and y
is not negative NaN, then total_order_less(x, y) == true
, x
is not positive NaN and y
is positive NaN, then total_order_less(x, y) == true
, x
and y
are NaNs with the same sign and x
's mantissa field is less than y
's, then total_order_less(x, y) == !std::signbit(x)
.
(C++20) | the result type of 3-way comparison that supports all 6 operators and is substitutable (class) |
(C++20) | performs 3-way comparison and produces a result of type std::weak_ordering (customization point object) |
(C++20) | performs 3-way comparison and produces a result of type std::partial_ordering (customization point object) |
(C++20) | performs 3-way comparison and produces a result of type std::strong_ordering , even if operator<=> is unavailable (customization point object) |
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