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From: net@opal.cs.tu-berlin.de (Oliver Laumann)
Newsgroups: comp.unix.wizards
Subject: Re: Socket datagram
Message-ID: <3333@kraftbus.cs.tu-berlin.de>
Date: 14 May 91 13:27:18 GMT
References: <11225@hub.ucsb.edu>
Organization: Technical University of Berlin, Germany
Lines: 21

In article <11225@hub.ucsb.edu> hubert@spica.ucsb.edu writes:
> Hi! I am testing the socket's datagram facility and I can't figure
> out why the following program doesn't work. The a.out give me
> error message like "bad address". Could someone explain it ?
> 
> 	if (recvfrom(s1, mesg4, sizeof(mesg4),0,&sock2, sizeof(sock2))==-1)
> 		perror("receive error\n");

The last argument of recvfrom() is of type int*, not just int (it's an
input-output parameter).  You initialize it with the size of the buffer
that will be filled with the address; recvfrom() fills it with the
actual size of the address stored in the buffer on return.

To fix your program, declare an additional int variable "fromlen" and
invoke recvfrom() like this:

   fromlen = sizeof(sock2);
   if (recvfrom(...,&sock2,&fromlen) ...

--
Oliver Laumann    net@tub.cs.tu-berlin.de  net@tub.UUCP  ol@gnu.ai.mit.edu