Re: Pointers in Ada

[di98mase@hotmail.com (Sebastian)]

Jeffrey Carter <spam@spam.com> wrote in message news:<0L1Wd.824$oO4.709@newsread3.news.pas.earthlink.net>...
> Sebastian wrote:
> 
> > package Mdp_Lld;
> >   type Message_Header is
> >      record
> >        Word_Count              : Byte;
> >        Command_Id              : Byte;
> >      end record;
> > 
> >      subtype Mdp_Message_Data is Byte(1..500);
> > 
> >      type A_Mdp_Message is
> >         record
> >           Header : aliased Message_Header;
> >           Data   : aliased Mdp_Message_Data;
> >         end record;
> > 
> >      type Driver_Msg_Ptr_Type is access all A_MDP_Message;
> > 
> >      procedure Put_Message
> >         (Msg_Buffer_Ptr : in out Client_Msg_Ptr_Type;
> > );
> 
> As you're no doubt aware, this won't compile. In addition to the syntax 
> error in the declaration of Put_Message, Client_Msg_Ptr_Type has not 
> been declared.
> 
> Before we can answer your questions, we need to know why you're using 
> pointers. What wrong with
> 
> procedure Put_Message (Message : in An_Mdp_Message);
> 
> ?
> 
> In Ada pointers are needed far more rarely than in some other languages. 
> Since you're not building a dynamic data structure, it's likely that you 
> don't need them. If you really do need them, it's probably a better 
> design to hide them from the clients of the package. That way you can 
> localize the memory management to your package.

Hi everybody

thanks for your answers. First, I have not written the code myself it
is a UDP/IP stack that I found as a open source. I would not use
pointers myself thats why I'm havning problems knowing how to
initialize them;) Anyway, sorry that the code does not compile but I
extracted it from the files and "tweaked" it to fit the forum.
Soo, in order to create a message and send it using Put_Message I have
to create a variable of the private type Client_Msg_Ptr_Type in "my
calling source code file" BUT in order to do that the calling code
must be within a child package to the Mdp_lld package otherwise the
private type is not visable, or am I missing something here? Also the
Outmessage has to be aliased and I have to write the code like:
My_Msg_Ptr := Outmessage'Access;

Will this work? Well I will try it on monday...I'll let you know..

Thanks,

Sebastian