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Newsgroups: comp.lang.ada
Date: Wed, 6 Feb 2019 22:41:26 -0800 (PST)
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Subject: Re: Ada x <whatever> Datagram Sockets
From: "Rego, P." <pvrego@gmail.com>
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Xref: reader01.eternal-september.org comp.lang.ada:55452
Date: 2019-02-06T22:41:26-08:00
List-Id: <comp.lang.ada>

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:
> >=20
> > Just the string "test". I also confirmed that the MQL container (uchar =
data[]) has really the size 5.
> >=20
>=20
> Right, Ada strings are not zero-terminated, and the size of the string ne=
eds=20
> to come from somewhere, which is why String'Input will interpret the firs=
t x bits (probably 32, but may depend on your platform) as the length. So i=
n this
> case, "test" becomes a big number and 'Input will most likely try to allo=
cate
> just under 2GB  on your stack (and probably at least twice, in order to c=
opy
> 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 sam=
e size, right?=20

(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;
)

>=20
> Don't use Ada stream attributes to communicate with other languages.
>=20
> 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, howe=
ver 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 c=
omments from g-sockets.ads with minimum modification. I don't think it woul=
d be wise to re-implement Ada Sockets pkg to be more efficient.