std::weak_order

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Utilities library

Type support (basic types, RTTI, type traits)
Dynamic memory management
Error handling
Program utilities
Variadic functions
Library feature-test macros
Date and time
Function objects
initializer_list (C++11)
bitset
hash (C++11)
integer_sequence (C++14)
Relational operators (deprecated in C++20)
rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=
Comparisons (C++20)
strong_order weak_order partial_order strong_equal weak_equal	strong_ordering weak_ordering partial_ordering strong_equality weak_equality	is_eqis_neqis_ltis_lteqis_gtis_gteq
common_comparison_category
Common vocabulary types
pair tuple (C++11) apply (C++17) make_from_tuple (C++17)	optional (C++17) any (C++17) variant (C++17)
Swap, forward and move
swap
exchange (C++14)
forward (C++11)
move (C++11)
move_if_noexcept (C++11)
Elementary string conversions
to_chars (C++17)
from_chars (C++17)
chars_format (C++17)
Type operations
declval (C++11)
as_const (C++17)
launder (C++17)

 

Defined in header <compare>
template< class T > constexpr std::weak_ordering weak_order(const T& a, const T& b);		(since C++20)

Compares two values using 3-way comparison and produces a result of type std::weak_ordering

Specifically,

• If the expression a <=> b is well-formed and its result is convertible to std::weak_ordering, returns that result.
• Otherwise, if the expression a <=> b is well-formed, but its result is not convertible to std::weak_ordering, then the function is defined as deleted.
• Otherwise, if the expression a <=> b is ill-formed, but the expressions a == b and a < b are both well-formed and convertible to bool,

• if a == b is true, returns std::weak_ordering::equivalent
• otherwise, if a < b is true, returns std::weak_ordering::less
• otherwise, returns std::weak_ordering::greater

• Otherwise, the function is defined as deleted.

Parameters

a, b

-

values to compare

Return value

A value of type std::weak_ordering, as described above.

See also

weak_ordering (C++20)	the result type of 3-way comparison that supports all 6 operators and is not substitutable (class)
strong_order (C++20)	performs 3-way comparison and produces a result of type std::strong_ordering (function template)
partial_order (C++20)	performs 3-way comparison and produces a result of type std::partial_ordering (function template)
weak_equal (C++20)	performs 3-way comparison and produces a result of type std::weak_equality (function template)