All Comparison and Ordering Facilities

All Comparison and Ordering Facilities

A compact scan page for equality, ordering categories, comparators, and three-way comparison support in modern C++.

How to use this reference page

Use reference pages to confirm names, categories, nearby facilities, and the constraints that matter before writing or reviewing code.

Scan the top of the page first to identify the primary types, functions, or algorithm families involved.
Use the nearby-page links when your question is really about a companion header, related algorithm family, or broader subsystem.
Validate tricky behavior with a small compileable example before relying on memory for details like invalidation, ordering, allocation, or lifetime rules.

All Comparison and Ordering Facilities

Comparison category types

std::strong_ordering
std::weak_ordering
std::partial_ordering
equality categories where available in the active standard/library mode

Operators and language support

==, !=, <, <=, >, >=
spaceship operator <=>
defaulted comparisons

Comparator objects and utilities

std::less, std::greater, std::equal_to
transparent comparators such as std::less<>
std::compare_three_way
range comparators such as std::ranges::less

Where ordering shows up in practice

ordered associative containers
sorting and binary-search style algorithms
custom domain types with structural comparisons

Practical rules

Prefer defaulted comparisons when memberwise semantics are correct.
Use strong ordering only when the domain truly guarantees it.
Be careful with floating-point and NaN-heavy domains; they typically imply partial ordering.

Example in practice

#include <compare>

struct Version {
    int major{};
    int minor{};
    auto operator<=>(const Version&) const = default;
};

int main() {
    return Version{1, 2} < Version{2, 0};
}