Question

What do you do when you have a set of .h files that has fallen victim to the classic ‘gordian knot’ situation, where to #include one .h means you end up including almost the entire lot? Prevention is clearly the best medicine, but what do you do when this has happened before the vendor (!) has shipped the library?

Here’s an extension to the question, and this is probably the more pertinent question — should you even attempt to disentangle the dependencies in the first place?;

Answer 1

I’ve done this on a C++ code base that was already split into many libraries (which was a good start).

I had to workout (or guess) which library was the most depended upon, which depended upon nothing else in the code base. I then processed each library in turn.

I looked at each module (*.cpp files) in turn and made sure that its own header was #included first and commented out the rest, then I commented out all the #includes in that header file and then re-compiled just that module to let the compiler tell me what was needed. I would un-comment the first header that seemed to be needed, and reviewed that one, recursing as necessary. It was interesting to see how many headers ended up not being needed.

Where only the name is needed (because you have a pointer or reference) use class name; or struct name;, which is called forward declaration and avoid #including the header file.

The compiler is very helpful in telling you what the dependencies are when you comment out #includes (you need to recompile with ALL the compilers you have to maintain portability).

Sometimes I had to move modules between libraries so that no pairs or groups of libraries were mutually dependant.