Interfacing to C: API with macros

[tmoran@acm.org]

> Again, the straightforward solution: thin wrapper in C, that itself is
> simple enough to be easily imported by Ada code.
>
> Again: is this THE solution?
>
> Looks like in order to write any nontrivial system software the poor
> Ada programmer has to start with an awful lots of wrappers - where is
> maintainability and productivity when you need them? ;-)
   If you are interfacing to something that isn't documented, then you
will indeed have to experimentally determine the interface, or make
a wrapper from unknown to known interface spec.
   Usually the interface is documented (though too often erroneously),
though you may have to look carefully to see, for instance, what some
bit-field packing macro is doing.  Once you know, you can write a
direct Ada interface.  Claw, for instance, uses a great number of Windows
API calls, and it uses no wrappers in C (though the whole point of Claw
is to give an Ada-flavor wrapper to the Windows API).  Many APIs
in the Windows world also have typelib descriptions that can be used
to automatically generate an Ada wrapper.