Re: Sending Variable Length Messages with GNAT.Sockets

[Simon Wright <simon@pushface.org>]

Simon Wright <simon@pushface.org> writes:

>    declare
>       Readable : my_array_type (1 .. number_of_array_elements);   
>    begin
>       my_array_type'Read (str, Readable);

I forgot to say, you need to be careful about the components of
records if you're going to let the compiler use the default
'Read/'Write.

If the C side says

  struct rec {
    char flag;
    int count;
  };

there will typically be 3 bytes of padding between flag & count, for 8
bytes on the wire.

If the Ada side says

  type Rec is record
     Flag : Interfaces.Unsigned_8;
     Count : Interfaces.Integer_32;
  end record;
  pragma Convention (C, Rec);

the 'Write will output *5* bytes; but an unchecked conversion to
Stream_Element_Array (1 .. 8) will succeed & do The Right Thing
(endianness permitting).