Theory on error handling?

Question

Most advice concerning error handling boils down to a handful of tips and tricks (see this post for example). These hints are helpful but I think they don\'t answer all question

Answer 1

Here is an awesome blog post which explains how error handling should be done. http://damienkatz.net/2006/04/error_code_vs_e.html

How to decide if an error should be handled locally or propagated to higher level code? Like Martin Becket says in another answer, this is a question of whether the error can be fixed here or not.

How to decide between logging an error, or showing it as an error message to the user? You should probably never show an error to the user if you think so. Rather, show them a well formed message explaining the situation, without giving too much technical information. Then log the technical information, especially if it is an error while processing input. If your code doesn't know how to handle faulty input, then that MUST be fixed.

Is logging something that should only be done in application code? Or is it ok to do some logging from library code. Logging in library code is not useful, because you may not even have written it. However, the application could log interaction with the library code and even through statistics detect errors.

In case of exceptions, where should you generally catch them? In low-level or higher level code? See question one.

Similar question: at what point should you stop propagating an error and deal with it? See question one.

Should you strive for a unified error handling strategy through all layers of code, or try to develop a system that can adapt itself to a variety of error handling strategies (in order to be able to deal with errors from 3rd party libraries). Throwing exceptions is an expensive operation in most heavy languages, so use them where the entire program flow is broken for that operation. On the other hand, if you can predict all outcomes of a function, put any data through a referenced variable passed as parameter to it, and return an error code (0 on success, 1+ on errors).

Does it make sense to create a list of error codes? Or is that old fashioned these days? Make a list of error codes for a particular function, and document it inside it as a list of possible return values. See previous question as well as the link.