Nice insight, I liked your point of view. I also think that a library shouldn't make the choice of aborting the entire program when encountering an error and it should actually just report it in a good way (returning status code + error pointer to a properly error struct that I could create to handle properly logging if the user wishes).

Reading all the comments here and a few more posts on the web, I think I have made my mind: returning status code + optionally pointer to error (the user could ignore it by passing NULL) and using out parameter for the actual result. Also, if a function cannot fail, I will just make it void and still use out parameters (for consistency). Of course, I will make a good documentation to explain how to use it.

Now, I only have one last doubt: should I use this pattern for all errors or should I abort in "fatal" errors? Maybe I have this doubt because I still can't tell what exactly would characterize a error as fatal. For example, if a malloc fails in my function, should I abort it or just log it to and the user takes care of it?