All Comparison Function Objects

All Comparison Function Objects

A compact scan page for comparison functors, transparent comparators, and ordering helpers used across algorithms and containers.

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 Function Objects

Core comparison functors

std::less
std::greater
std::equal_to
std::not_equal_to
std::less_equal
std::greater_equal

Transparent and ranges-oriented forms

transparent forms such as std::less<>
std::ranges::less
std::ranges::greater
std::compare_three_way

Where they are used

ordered associative containers
sorting and ordering algorithms
binary-search-style algorithms
domain-specific comparator injection points

Practical rules

Prefer transparent comparators when heterogeneous lookup is desirable.
Keep comparator semantics strict and stable; broken comparators break container and algorithm assumptions.
Use compare_three_way and <=> when the domain benefits from explicit ordering-category modeling.

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};
}