How to use stdafx.h properly?

Question

What is the proper way to use stdafx.h, in terms of separating dependencies?

If I put everything in there, then my compiles are blazing fast, and all I need to say in any file is

#include "stdafx.h"

with the caveats that:

1. I no longer know which files depend on which headers.
2. It reduces modularity, making my code less reusable.
3. I can no longer separate C #includes from C++ ones (e.g. cstring versus string.h) without a great deal of pain. (Speaking of which, does this even matter?)

If I put nothing in there, I can organize everything well -- but then my compiles slow down dramatically.

If I put everything in there and also include every header in my individual files, then I get the best of both worlds, with the caveat that now I have to keep track of synchronization issues.

Is there a well-known/well-accepted solution to this problem?

Answer 1

You shouldn't put your own header files in stdafx.h since your code is likely to change and will cause your whole program to recompile.

I usually put standard headers and other libraries in there, such as all boost includes.

Answer 2

When using precompiled headers, you should make sure your project compiles cleanly even without PCH present (so treat it as optimisation, not a replacement for includes in every TU). Aside from that, don't put absolutely everything in there (and more importantly, don't ever put headers from your own project — PCH should contain only those that don't change or change very rarely — system libraries, external dependencies), but rather try to keep most used/biggest things precompiled.