Very Computer

Hi,

   The synopsis of send() is

      #include <sys/socket.h>
      int send(int s, const void *msg, int len, int flags);

in HP-UX.  Could somebody tell me what is the meaning of "const void *msg".
I try to send a long integer from client to server by the following command

      long int event;
      ...
      send(socketFD, &event, sizeof(event), 0);
      ...

But it can't work and I got the error message

      "error: Invalid argument"

What's wrong ??  Thanks a lot :)

    Kuang-chun Cheng

If the error message you are refering to is from the compilier, try
casting "event".  i.e.:

send(socketFD,(const void *)&event, sizeof(event),0);

That should work.  "const void *" usually means you can pass a pointer to
any data type, but, you should cast it.

Hope that helps.

-Andrew L. Sandoval

      long int event;
Send requires a character buffer of length len. The following example
illustrates this.
char* buf = "This is a message";
send(sockFd,buf,strlen(buf),0);
                                - madhav

This is a nice example, but does not solve his problem.  I encountered this
problem not to long ago and resolved it with a few extra lines of code...

example:
       long event;
       char buf[sizeof(long)];

              memcpy(&event,buf,sizeof(event));
              send(socketFD,buf,sizeof(buf),0);

Remember that send is a specialized form of write (which you can use as
well)
Also remember to check the value returned by send or write to make sure all
your data was sent.  You might have to set up a loop to send all the data
in case it wasn't.  This strange behavior is a feature of the networking
code inside the OS.

               -- Zachary F. Roadhouse

WWW: http://www.netspace.org/~zack
***************************************************

various people commented on this problem:

Quote:> >       long int event;
> > >      ...
> > >      send(socketFD, &event, sizeof(event), 0);
> > >      ...

> > >But it can't work and I got the error message
> > >      "error: Invalid argument"

suggesting copying it to a buffer, and passing that buffer to send.
this is RIDICULOUS!  folks, you _are_ smarter than the compiler,
sometimes at least and this is what casts are for: when the prototype
expects a char*, and it really _should_ be a void*, you need a cast:
        long event;
        send(socketFD, (char*) &event, sizeof(event), 0);

remember, send predates sensible typechecking in C (Ansi).  SunOS 4
and osf/1 seem to like the (broken) char* parameter, whereas hpux,
linux and irix have the more sensible:
      int send(int s, const void *msg, int len, int flags);

regards, mark hahn.
--

Hey guys. You're making it far too difficult.
    send(fd, (char *) &event, sizeof(event), 0);

Don't copy. You'll kill the performance.  But note that on boxes where
the byte order might be differnet this won't be well received.
So maybe....
    long event, event2;
    event2 = htonl(event);
    send(fd, (char *) &event2, sizeof(event2), 0);

Dave