Re: Importing C function with variable argument list

[Jacob Sparre Andersen <sparre@nbi.dk>]

Natasha Kerensikova wrote:

> Another significant difference between varargs and regular arguments
> is "type promotion". Briefly, char and short types are promoted to int
> when they are part of a variadic argument, while they are not when
> they are an explicit argument.
>
> So the following will probably fail more reliably than previous
> examples:

I'm afraid I have to disappoint you.  Your example (here with test
driver) works fine on Debian/stable (armv6l):

% cat c_varargs.adb
with Interfaces.C;
procedure C_Varargs is
   function Print_Short (Format : in Interfaces.C.char_array;
                         Value  : in Interfaces.C.short)
     return Interfaces.C.int;
   pragma Import (C, Print_Short, "printf");
   use type Interfaces.C.char_array;
   Result : Interfaces.C.int;
begin
   Result := Print_Short ("%hd" & Interfaces.C.char'Val (10), 42);
end C_Varargs;
% gnatmake c_varargs
[...]
% ./c_varargs
42
%

Greetings,

Jacob
-- 
"In space, no-one can press CTRL-ALT-DEL"
                                        -- An Ada programmer