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* GNAT, Windsock, and DLLs
@ 1998-04-14  0:00 Do-While Jones
  1998-04-14  0:00 ` Barry Scott
                   ` (3 more replies)
  0 siblings, 4 replies; 7+ messages in thread
From: Do-While Jones @ 1998-04-14  0:00 UTC (permalink / raw)



The general question is, "How does GNAT link Ada 95 programs with Windows
95 DLLs?"

More specifically, "How can GNAT make use of the Berkeley-like socket
services in windsock.dll?"

In particular, "What do I need to do to get a demo program (included at
the end of this message) to call the gethostname service in windsock.dll?"

Background

Several years ago, I wrote a collection of Network Interface packages
which allow Ada 83 programs (compiled using the Telesoft Telegen 2
compiler on a Sun Sparcstation 2) to call the Berkeley BSD socket
routines.  These thick bindings gave me handy abstractions that send and
receive UDP broadcasts, and implement TCP/IP clients and servers. 

A couple years ago I ported these packages from our Sun workstations to
GNAT (Ada 95) on Silicon Graphics in no time at all.  This was easily done
because the Silicon Graphics was using a UNIX operating systems with
Berkeley sockets.

A few months ago I tried to port these same packages to GNAT (Version
3.10) on a Windows 95 machine.  Windows 95 comes with a dynamically linked
library (DLL) called windsock, which emulates all the Berkeley socket
services.  One of the simplest of these is gethostname, which returns a
character string containing the name of the host computer. 

The Problem

Use gnatchop to divide the program at the end of this message into three
compilation units.  Then use gnatmake to compile and link ni09td01. 
(Network Interfaces, component 9, Test Demo program 1.) The program
compiles, but fails at the link stage with an error message that says
there is an "undefined reference to 'gethostname' in get_host.adb".
Clearly, GNAT doesn't know about the gethostname service in windsock.dll. 

The GNAT UserUs Guide section on "Search Paths for gnatbind" (yes, I'm one
of those few people who read the documentation) says that you can tell the
linker to look for modules in other directories in several ways.  One of
these ways is to set the environment variable ADA_OBJECTS_PATH.  So, I set
ADA_OBJECTS_PATH to "C:\WINDOWS\SYSTEM" where the windsock.dll is (on my
system, at least). That didn't work. 

I suspect gnatbind is looking for a ".o" file, not a ".dll" file.

I know very little about C, and even less about Windows 95.  I suspect
this problem is more of a C/Windows 95 problem than an Ada problem.

What is the solution?

Do I have to write a zillion (well, actually eight, since I only use
socket, bind, accept, fcntrl, open, close, read, write, and gethostname) 
little C programs that call each windsock service individually, and put
their ".o" files somewhere that GNAT can find them?  Is there a way to get
GNAT to use the windsock.dll directly? 

If there is a simple solution, I'm sure many readers of Comp.lang.ada
would find it useful. 

Thanks in advance,

Do-While Jones
-------------------------------------------------------------

--                      ni09ks01.ada
--                      13 December 1994

--                      Do-While Jones
--                      324 Traci Lane
--                      Ridgecrest, CA 93555
--                      do_while@ridgecrest.ca.us

--with NETWORK;  -- part NI02

package GET_HOST is

  function Name return string;
    -- Tells you the name of the computer that is executing
    -- the program.

  --function Network_Address return NETWORK.Address_numbers;
    -- Tells you the network address  of the computer that
    -- is executing the program.

end GET_HOST;

--                      ni09kb01.ada
--                      13 December 1994

--                      Do-While Jones
--                      324 Traci Lane
--                      Ridgecrest, CA 93555
--                      do_while@ridgecrest.ca.us

with SYSTEM;

package body GET_HOST is

  --- Interface to UNIX service ---

  function gethostname(
    name_receiver : SYSTEM.Address;
    namelen       : integer)
    return integer;
  pragma Interface(C, gethostname);

  ---------------------------------

  function Name return string is
    -- Assume the name will be 20 characters
    -- or less.
    C_STRING : string(1..21)
      := (others => ASCII.NUL);
    UNIX_RESULT : integer;
    LENGTH      : integer;
  begin
    -- Call a UNIX service to put the name
    -- in C_STRING.
    UNIX_RESULT := gethostname(
      C_STRING(1)'ADDRESS, C_STRING'LENGTH);
    if UNIX_RESULT /= 0 then
      -- UNIX failure.
      return "HOST_NAME_ERROR";
    end if;

    -- Find out how long the string is.
    LENGTH := 0;
    for i in C_STRING'RANGE loop
      exit when C_STRING(i) = ASCII.NUL;
      LENGTH := i;
    end loop;

    -- Return the non-null characters of the string.
    return C_STRING(1..LENGTH);
  end Name;

  --function Network_Address
    --return NETWORK.Address_numbers is
  --begin
    --return NETWORK.Host_Number(Name);
  --end Network_Address;

end GET_HOST;

--                      ni09td01.ada
--                      13 December 1994

--                      Do-While Jones
--                      324 Traci Lane
--                      Ridgecrest, CA 93555
--                      do_while@ridgecrest.ca.us

with TEXT_IO,
     --NETWORK,   -- part NI02
     GET_HOST;  -- part NI09

procedure NI09TD01 is
begin
  TEXT_IO.Put_Line("This machine is "
    & GET_HOST.Name & ".");
  --TEXT_IO.Put_Line("It is at address "
    --& NETWORK.Image(GET_HOST.Network_Address)
    --& ".");
end NI09TD01;






^ permalink raw reply	[flat|nested] 7+ messages in thread
end of thread, other threads:[~1998-04-16  0:00 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
1998-04-14  0:00 GNAT, Windsock, and DLLs Do-While Jones
1998-04-14  0:00 ` Barry Scott
1998-04-14  0:00 ` Tom Moran
1998-04-16  0:00 ` Jerry van Dijk
1998-04-16  0:00 ` Stephen Leake
1998-04-16  0:00   ` Martin C. Carlisle
1998-04-16  0:00   ` Jerry van Dijk

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