Hi,

I am porting application from Windows to Linux. I use Sockets unit.

There is defined on Windows (and also on BeOS, FreeBSD, OS2):
   INVALID_SOCKET = TSocket(Not 0); // or -1
   SOCKET_ERROR = -1;

But not for Linux. Does it means, that result of unsuccessfull call to Sockets.FPSocket can be other than -1 ?
(in fcl-net is used test for -1 to check invalid socket so I think, that it is crossplatform ... if yes why isn't INVALID_SOCKET defined also for Linux in RTL?)

Thanks

-Laco.

In our previous episode, LacaK said:

Under *nix socket calls are just general runtime calls, and they use the same convention and constants for errorhandling as all other calls.

Under Windows, the winsock part is separate from the C runtime and uses own constants. Invalid_socket is a winsock constant added to sockets for convenience (but not portable). Strictly speaking we could add a "platform;" now to it.

I guess I did't want to encourage winsock (which is the odd one out) coding in general *nix code.

Because we don't want to pollute the unix units with windows-isms.

If it is a POSIX defined constant, we can add it, but if it is not: too bad.

Michael.

Under *nix socket calls are just general runtime calls, and they use the same convention and constants for errorhandling as all other calls.

As I know "nothing" about Linux, then it is safe to check?:

   socket := Sockets.FPSocket(...);
   if socket = -1 then // invalid socket returned due to error ...

This technique is used in fcl-net which should be cross-platform. So I am right, when I say that also in Linux invald socket = -1 (in other words: in case of error syscall() returns always -1)

Becuase in other place I see another test "if socket < 0 then ..." (which may mean that any negative value can be returned)

L.

Il 28/03/2017 12:34, LacaK ha scritto:

Most likely this is only because "socket < 0" is faster to write than "socket = -1" :-)

From Linux man page for socket:

RETURN VALUE On success, a file descriptor for the new socket is returned. On error, -1 is returned, and errno is set appropriately.

Giuliano

Thanks for all repies.
For now I add to my unit:

{$IFDEF UNIX}
// not defined for POSIX; Linux syscall() returns -1 in case of error
const
   INVALID_SOCKET = -1;
   SOCKET_ERROR = -1;
{$ENDIF}

and later I use (in cross-platform code):

   Fsocket := fpsocket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
   if Fsocket = INVALID_SOCKET then ...

-Laco.

Most likely this is only because "socket < 0" is faster to write than "socket = -1" :-)

And is probably faster to execute on most processors which offers a sign flag.