Re: Projects for beginners

[Richard Earnshaw <rearnsha at arm dot com>]

>     It also effectively sets those dependencies in concrete. If, for any
>     reason, the dependencies change for a particular header, you have to
>     change all sources that include it.
> 
> From a conceptual point of view, you do anyway.  A header is a specification
> of something which is implemented in a .c file.  If the specification
> of something changes, you have to look at all callers to make sure they
> reflect the change of specification.

Not necessarily.  Header files describe a set of interfaces.  If I add a 
new interface to a particular module it may require that a new header be 
included first (as a hypothetical example rtl.h might change from not 
requiring bitmap.h to requiring it).  However, unless I make use of that 
new interface in a particular C file, say wibble.c, nothing there has 
changed.  With the nested includes model I don't have to change wibble.c 
at all.  With your flat includes model I have to add the new #include to 
wibble.c.

IMO each C file should directly include just those header files whose 
interfaces it directly uses.  It shouldn't have to directly include a 
different set just to make the header file valid.  In this way, the list 
of header files at the top of a file is the list of interfaces used by 
that file.

R.