Delivery-Date: Fri Aug 29 19:20:57 2008
Message-Id: <200808300228.m7U2S08C029244@bourbon.usc.edu>
To: cs551@merlot.usc.edu
Subject: Re: Regarding CS-551 Warmup Project-1
Date: Fri, 29 Aug 2008 19:28:00 -0700
From: Bill Cheng <william@bourbon.usc.edu>

Someone wrote:

  > Lecture 2 slide 14 uses the following line to set the server's address in
  > the client code.
  > serv_addr.sin_addr.s_addr  = inet_addr("nunki.usc.edu");
  > 
  > When I do this my connect fails and gives me the following error "Network is
  > unreachable". It works if I replace "nunki.usc.edu" with the IP address of
  > the server.
  > Since the input to the commandline has to be hostname, I am using
  > gethostbyname() function.
  > 
  > What might be the reason that the code given in the slides is not working?

Hmm... I don't have Steven's book with me.  I guess I must
have copied something incorrectly.  The man pages of inet_addr()
says:

     The inet_addr() and inet_network() functions interpret char-
     acter  strings  that represent numbers expressed in the IPv4
     standard `.' notation, returning numbers suitable for use as
     IPv4  addresses  and IPv4 network numbers, respectively. The
     inet_makeaddr() function uses an IPv4 network number  and  a
     local  network  address  to  construct  an IPv4 address. The
     inet_netof() and inet_lnaof()  functions  break  apart  IPv4
     host  addresses,  then  return  the network number and local
     network address, respectively.

So, it should be used if the argument passed to it is a string
that has dotted numbers, e.g., "68.181.201.3".  So, you should
only call inet_addr() if the first character in a hostname is
between '0' and '9'.  Otherwise, you should probably call
gethostbyname().

Sorry about the bug in the slides.  I'll fix it when I have the
book in front of me.
--
Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>