Re: Importing C structs?

[Freejack <freejack@nospam.net>]

On Wed, 30 Jul 2003 16:52:49 -0400, chris wrote:

 
> Make an Ada record corresponding to that type.  Map it's fields to
> things from interfaces.c and other records.  Then use
> 
> pragma Convention(C, DBType);
> 
> I think!
> 
> This is from my ongoing work on a libjpeg binding...
> 
>     type Jpeg_Error_Mgr is record
>        Error_Exit          : Error_Exit_Handler; Emit_Message        :
>        Emit_Message_Handler; Output_Message      :
>        Output_Message_Handler; Format_Message      :
>        Format_Message_Handler; Reset_Error_Mgr     :
>        Reset_Error_Handler; Msg_Code            : C.Int; Msg_Parm       
>            : System.Address; Trace_Level         : C.Int;
>        Num_Warnings        : C.Long;
>        Jpeg_Message_Table  : Jpeg_Message_TableT; Last_Jpeg_Message   :
>        C.Int;
>        Addon_Message_Table : Jpeg_Message_TableT; First_Addon_Message :
>        C.Int;
>        Last_Addon_Message  : C.Int;
>     end record;
> 
>     pragma Convention (C, Jpeg_Error_Mgr);
 
 
> HTH,
> Chris
 
I've been toying with the idea of creating a generic procedure for these
types of situations. I dont know if Ada will let me get away with it
though.

i.e.

with Interfaces.C;
with Interfaces.C....blah blah blah;

generic
	type foo is new private(<>);
	type bar is new private(<>);
package dooh_dah is

	package Some_C renames Interfaces.C.blah;

private

	function cast_to_C(foo : in Ada_Type) return Is_Success;
	
	-- etc..etc..etc...
	
end dooh_dah;

Now, I realize that the Interfaces library provides a limited set of
functions and procedures for performing some of the operations I'm
talking about here. But as far as I know everything has to be set up
explicitly. I'm hoping theres a way to have the compiler do an automatic
cast (or export) to a C function depending the execution context.

But that type of programming is a little ways down the road. I dont have
a need for this yet, but maybe later.

Freejack.