What are the differences between unions and std::variant in C++17?

What are the differences between unions and std::variant in C++17?

In C++17, unions are a way to store different data types in the same memory location, but they have limitations. std::variant, on the other hand, is a type-safe union that can hold one of several types and provides better safety and usability.

Can you explain the safety features of std::variant?

Sure! std::variant ensures type safety by only allowing access to the currently active type. It also provides functions like std::get and std::visit to safely retrieve or operate on the value, throwing exceptions if the type doesn't match.

Are there any performance differences between using unions and std::variant?

Yes, unions can be more efficient in terms of memory usage since they don't have the overhead of type management. However, std::variant may introduce some overhead due to its type safety features, but it often leads to safer and more maintainable code.

When should I use std::variant instead of unions?

You should use std::variant when you need type safety and want to avoid undefined behavior. If you need a simple, low-level data structure without the need for type safety, unions might be appropriate.