How can you safely use floating point values as keys in `std::map` and avoid unexpected behavior?

Floating Point Keys in std::map: Avoiding Comparisons with Epsilon

When using double types as keys in a std::map, floating point precision issues can arise. Comparing values using an epsilon threshold, while commonly used, can violate container ordering requirements and lead to undefined behavior.

To address this, a safer approach is to define a custom comparison operator to handle NaN values and avoid direct key comparisons. Additionally, using std::multimap or std::multiset can accommodate multiple key values, reducing the risk of unexpected behavior.

To perform approximate searches using double keys, a helper function can be used to return a range of elements close to the target value, controlled by an epsilon parameter. This range can then be iterated over to locate the desired key if it exists. Alternatively, a key existence check function can be implemented based on the range lookup.

It is generally advisable to avoid using floating point values as keys in std::set or std::map due to their potential to introduce errors. Excluding them from the more precise interface can mitigate the risk of bugs caused by unexpected value comparisons. However, using them for automatically sorted collections, where exact order is not critical, can still be beneficial.

The above is the detailed content of How can you safely use floating point values as keys in `std::map` and avoid unexpected behavior?. For more information, please follow other related articles on the PHP Chinese website!