Re: Import C

["Nando" <nando89@terra.es>]

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Thans you very much!!! :)))

It's a very complete information, with examples and comments. I'm going to
try now everything you told. I think every thing is going to be all right ;)

Thanks again
    Fernando

"Ludovic Brenta" <ludovic.brenta@insalien.org> escribi� en el mensaje
news:m3wu7elr4e.fsf@insalien.org...
> "Nando" <nando89@terra.es> writes:
>
> > Hello!!!
> > I need make an Ada application. I need send and receive some information
> > to/from the serial port communication (from PC to another device).
> >
> > I don't know how to do it in Ada, but I know to do it in C/C++. I have
found
> > the command "pragma inport(C, ...)" but I don't know how it works :((
> >
> > My questions:
> > * Is enough the .C and .H files or I need the object file?
>
> The Ada toolchain needs the object file only.  The .C and .H file are
> useful only for you to see the prototype for the function you want.
>
> > * How my Ada code know what file has my subrutine? i.e., where I say in
my
> > Ada source code what files to include?
>
> The Ada compiler will not include anything.  The linker will link your
> object file produced from C with the object files produced from Ada.
>
> > If you could give me a little example or documentation you would help me
> > very much.
>
> You need to redeclare your C function in Ada, and then Import it.
> Suppose yourt .H file has this prototype:
>
> extern int foo(int a, int b);
>
> then you need to write this in an Ada source file:
>
> package Binding_To_External_Library is
>    function Foo (A, B : Integer) return Integer; -- redeclare in Ada
>    pragma Import (Convention => C, Entity => Foo, External_Name => "foo");
> end Binding_To_External_Library;
>
> The External_Name is the name that the function has in the object (not
> C source) file.  Be careful with certain C compilers that insert an
> underscore before the function name; the External_Name might be
> "_foo".  I would advise not to import a C++ method because the name
> mangling and the "this" pointer are sources of headaches.  Write a C
> wrapper and import that instead.
>
> If your function uses structures, you also need to declare a
> corresponding type in Ada and use pragma Convention (C) on them.
>
> There are many existing bindings which you can find on the web.  Thick
> bindings are better.  A thick binding is one that replaces error codes
> (returned from the C functions) into exceptions, that perform range
> checking, and that are more type-safe than thin ones.  For example,
> suppose your C header file defines these:
>
> /* Values for parameter A passed to foo */
> #define NO 0
> #define YES 1
> #define MAYBE 2
> #define MAYBENOT 3
>
> /* Your program will crash if B is larger than this.  You're warned. */
> /* Oh, by the way, it will also crash if B < 0. */
> #define MAX_VALUE_FOR_B 100
>
> /* Values returned by foo */
> #define ERROR -1
> #define OK 0
>
> extern int foo(int a, int b);
>
> Then your thick binding would look like this:
>
> package Thick_Binding is
>    Foo_Error : exception;
>    type Assessment is (No, Yes, Maybe, Maybe_Not);
>    pragma Convention (C, Assessment);
>    type Safe_Value_For_B is new Integer range 0 .. 100;
>    pragma Convention (C, Safe_Value_For_B);
>    procedure Foo (A : Assessment; B : Safe_Value_For_B);
>    --  A type-safe procedure that always checks error codes.  The compiler
>    --  ensures that you always call it with safe values for B.
> end Thick_Binding;
>
> package body Thick_Binding is
>    procedure Foo (A : Assessment; B : Safe_Value_For_B) is
>       --  Hide the ugly and error-prone C function
>       function Internal (A, B : Integer) return Integer;
>       pragma Import (C, Internal, "foo"); -- or maybe "_foo"
>    begin
>       if Internal (Assessment'Pos (A), Integer (B)) = -1 then
>          raise Foo_Error;
>       end if;
>    end Foo;
> end Thick_Binding;
>
> HTH
>
> --
> Ludovic Brenta.