Precompiled headers: do's and don'ts?

Question

I know precompiled headers are used for speeding up compilations, but are there any do's and don'ts to what files I should include in them? For example, I have a project that uses a lot of boost libs so I just include the boost header files in stdafx.h (I'm using VS2008). Should I include every standard header file in them, too? Will this increase the size of my executeable even if I, for example, include <vector> but never use std::vector? Is it a bad idea to include my own project's header files in stdafx.h?

Answer 1

Pre-compiled headers don't affect the size of your executable, only the compilation speed. Since they are pre-compiled, they don't have to be re-compiled all the time. Windows.h is the primary beneficiary of this feature.

Answer 2

Generally speaking, every header file that you use across the application and that doesn't change often should go into the precompiled header file. This will speed up compilation because the precompiled header file gets compiled only once.

If you add a header file which changes often, you'll miss the point of the precompiled header file, because this often-changing header file will cause your whole project to recompile, possibly unnecessarily.

Specifically, defines a template class, so if you won't use std::vector, the overhead will not be big. However, I would advise against adding header files - however standard and generic - if you don't really need them. There IS some overhead to the compilation time, the binary size, and it could cause conflicts later in the project, so why add something if you don't really need it?

Answer 3

It's a good idea to include the c++ standard header-files and the boost library headers and any other headers from third party libraries that you frequently use. This will not affect the size of your executable.

However, you should not include headers from your own project, since the whole project needs to be rebuild whenever you make changes in these headers.