Question

I am involved in a contest, and in one event we have debugging questions. I have to design some really good debugging problems in C and C++.

How can I create some good problems on debugging? What aspects should I consider while designing the problems?

Answer 1

My brainstorming session:

Memory leaks of the subtle sort are always nice to have. Mess around with classes, constructors, copy-constructors and destructors, and you should be able to create a difficult-to-spot problem with ease.

One-off errors for array loops are also a classic.

Then you can simply mess with the minds of the readers by playing with names of things. Create variables with subtly different names, variables with randomized (AND subtly different) names, etc. and then let them try and spot the one place where you’ve mixed up length and lenght. Don’t forget about casing differences.

Calling conventions can be abused to create subtle bugs too (like reversing the order of parameters).

Also let’s not forget about endless hours of fun from tricky preprocessor defines and templates (did you know that C++ templates are supposedly Turing-complete?) Metaprogramming bugs should be entertaining.

Next idea that comes to mind is to provide a correct program, but flawed input data (subtly, of course). The program will then fail for the lack of error checking, but it will be some time until people realize that they are looking for problems in the wrong place.

Race conditions are often a difficult to reproduce and fix, try to play with multithreading.

Underflows/overflows can be easily missed by casual inspection.

And last, but not least – if you’re a a programmer, try remembering what was the last big problem that you spent two weeks on solving. If you’re not a computer programmer, try to find one and ask them. I’m a .NET programmer, so unfortunately my experiences will relate little to your requirement of C/C++.