Re: Ada x <whatever> Datagram Sockets

["Rego, P." <pvrego@gmail.com>]

On Thursday, February 7, 2019 at 4:00:11 AM UTC-2, Egil H H wrote:
> > > On Wednesday, February 6, 2019 at 6:10:37 PM UTC-5, Rego, P. wrote:
> > 
> > Just the string "test". I also confirmed that the MQL container (uchar data[]) has really the size 5.
> > 
> 
> Right, Ada strings are not zero-terminated, and the size of the string needs 
> to come from somewhere, which is why String'Input will interpret the first x bits (probably 32, but may depend on your platform) as the length. So in this
> case, "test" becomes a big number and 'Input will most likely try to allocate
> just under 2GB  on your stack (and probably at least twice, in order to copy
> the result into your string).
A C++ uchar in Windows machine is usually 1 byte, so assuming that both use the same signature, both messages (from C++ and from Ada) should be of same size, right? 

(I checked both send commands used by Ada sockets and MQL sockets, and they both are using standard win32 signatures, I mean for C++ case

int sendto(
  SOCKET         s,
  const char     *buf,
  int            len,
  int            flags,
  const sockaddr *to,
  int            tolen
);

and in Ada case a imported function
   function C_Sendto
     (S     : C.int;
      Msg   : System.Address;
      Len   : C.int;
      Flags : C.int;
      To    : System.Address;
      Tolen : C.int) return C.int;
)

> 
> Don't use Ada stream attributes to communicate with other languages.
> 
> And, as some will tell you, don't use them at all, especially for arrays, as
> each array element may end up being transferred as a single data packet, destroying performance.

This is quite controversial, in this case. I'd usually agree with you, however the use of Ada stream is not by choice. The whole GNAT Ada package uses Ada streams, and actually the above code was entirely extracted from the comments from g-sockets.ads with minimum modification. I don't think it would be wise to re-implement Ada Sockets pkg to be more efficient.