Discussion

If one header file won't work unless the file that includes it also includes another header, that's gauche and puts unnecessary burden on that header file's users.

Years ago, some experts advised that headers should not include other headers because of the cost of opening and parsing a guarded header multiple times. Fortunately, this is largely obsolete: Many modern C++ compilers recognize header guards automatically (see Item 24) and don't even open the same header twice. Some also offer precompiled headers, which help to ensure that often-used, seldom-changed headers will not be parsed often.

But don't include headers that you don't need; they just create stray dependencies.

Consider this technique to help enforce header self-sufficiency: In your build, compile each header in isolation and validate that there are no errors or warnings.