Exception Handling in Hybrid Environments
Error handling is hard. Mixing multiple mechanisms is harder. The only thing that's even harder is explaining why your system doesn't handle errors properly. Different situations call for different solutions.
Sometimes avoiding exceptions is the right thing to do. Here are a few factors in favor of this approach:
- You maintain an existing system that doesn't use exceptions.
- The piece you work on is performance critical (pending profiling).
- Team members are not familiar with exception handling and are not keen on learning.
If you have already made the decision to use exceptions, you can pick and choose your battles. Not every function must throw exceptions and you probably don't want to convert the error-handling style of a large existing code base. Use exception handling in new code and where it makes sense. For example, if there is a complex piece of existing code that's buggy and tends to mismanage resources when errors occur, it is probably a good candidate for conversion. There is a good chance that the design is not optimal to begin with so while you refactor it, you can also convert it to use exception handling. You would be surprised how small the code can get with automatic objects managing cleanup of resources in destructors.
Catch exceptions on the interoperability border. When you need to interface with another component, you must conform to its API of course (unless you define that API, then the other party has to conform). If this API involves returning error codes or setting errno or any other error-handling reporting mechanism, you must not leak unhandled exceptions. It doesn't mean that you can't use exceptions in this case. It just means that you should catch your own exceptions internally in each API method/function and map your exceptions to the appropriate API convention.
The reverse is also true. If your code is heavily exception oriented and you call into some nonexception API, you don't have to deal with yet another error mechanism. You can wrap all the calls through this API in an object that converts API error codes to exceptions.