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From: chris@umcp-cs.UUCP (Chris Torek)
Newsgroups: net.unix-wizards
Subject: Re: Mildly exotic socket related system call problem - anyone help?
Message-ID: <1701@umcp-cs.UUCP>
Date: Mon, 26-May-86 03:31:12 EDT
Article-I.D.: umcp-cs.1701
Posted: Mon May 26 03:31:12 1986
Date-Received: Tue, 27-May-86 07:37:15 EDT
References: <189@comp.lancs.ac.uk>
Reply-To: chris@maryland.UUCP (Chris Torek)
Organization: University of Maryland, Dept. of Computer Sci.
Lines: 46

In article <189@comp.lancs.ac.uk> david@comp.lancs.ac.uk
(David Coffield) writes:
>... I need to get a machine address from the user e.g. "150.0.0.11"
>(in that format, as a string) and compare the network number of that
>address with the network number of the address of the machine on
>which the program is executing.

I would suggest using `inet_addr()' and then `inet_netof()', but:

>Now about a year ago I discovered that "inet_addr" caused core dumps
>every time you called it ...

I presume you have declared them and used them like so:

	u_long inet_addr();
	int inet_netof();	/* assumes int holds >= 24 bits, but... */
	int net;
	struct in_addr t;

	t.s_addr = inet_addr(string);
	net = inet_netof(t);

>So, questions as follows:
>1. Can anyone suggest a way round this problem?

Well, you can simply run atoi() on the first number to discover
whether the network is class A (< 128), B (128 to 191), or C
(>= 192).  If B, you need the next number; if C, the next two.
You then have the network.  Apply the same procedure to the
local address, and compare the strings.

>2. Does 4.3 have fixed "inet*" routines??

Yes.

>3. If so can anyone mail me a copy of working ones???

Hrum.

>4. Was 3. an illegal question????

Probably.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 1516)
UUCP:	seismo!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@mimsy.umd.edu