Is GetLastError() kind of design pattern? Is it good mechanism?

Question

Windows APIs uses GetLastError() mechanism to retrieve information about an error or failure. I am considering the same mechanism to handle errors as I am writing A

Answer 1

Exception handling in unmanaged code is not recommended. Dealing with memory leaks without exceptions is a big issue, with exception it becomes nightmare.

Thread local variable for error code is not so bad idea, but as some of the other people said it is a bit error prone.

I personally prefer every method to return an error code. This creates inconvenience for functional methods because instead of:

int a = foo();

you will need to write:

int a;
HANDLE_ERROR(foo(a));

Here HANDLE_ERROR could be a macro that checks the code returned from foo and if it is an error propagates it up (returning it).

If you prepare a good set of macros to handle different situations writhing code with good error handling without exception handling could became possible.

Now when your project start growing you will notice that a call stack information for the error is very important. You could extend your macros to store the call stack info in a thread local storage variable. That is very useful.

Then you will notice that even the call stack is not enough. In many cases an error code for "File not found" at line that say fopen(path, ...); does not give you enough information to find out what is the problem. Which is the file that is not found. At this point you could extend your macros to be able to store massages as well. And then you could provide the actual path of file that was not found.

The question is why bother all of this you could do with exceptions. Several reasons:

1. Again, Exception handling in unmanaged code is hard to do right
2. The macro based code (if done write) happens to be smaller and faster than the code needed for exception handling
3. It is way more flexible. You could enable disable features.

In the project that I am working at the moment I implemented such error handling. It took me 2 days to put in a level to be ready to start using it. And for about a year now I probably spend about 2 weeks total time of maintaining and adding features to it.