<QtCompare> - Classes and helpers for defining comparison operators

Function Documentation

[since 6.7] template <typename LeftType, typename RightType> auto qCompareThreeWay(const LeftType &lhs, const RightType &rhs)

Performs the three-way comparison on lhs and rhs and returns one of the Qt ordering types as a result. This function is available for both C++17 and C++20.

The actual returned type depends on LeftType and RightType.

This method is equivalent to

using Qt::compareThreeWay;
return compareThreeWay(lhs, rhs);

where Qt::compareThreeWay is the Qt implementation of three-way comparison for built-in types.

The free compareThreeWay functions should provide three-way comparison for custom types. The functions should return one of the Qt ordering types.

Qt provides compareThreeWay implementation for some of its types.

Use this function primarly in generic code, when you know nothing about LeftType and RightType.

If you know the types, use

• Qt::compareThreeWay for built-in types
• compareThreeWay for custom types

Use operator<=>() directly in code that will only be compiled with C++20 or later.

This function was introduced in Qt 6.7.

See also Qt::partial_ordering, Qt::weak_ordering, and Qt::strong_ordering.