Date: Fri, 21 Aug 1998 19:05:17 +0000 From: Mike Smith <mike@smith.net.au> To: Phil Gilley <pgilley@metronet.com> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: Stupidity or compiler bug? Message-ID: <199808211905.TAA11658@dingo.cdrom.com> In-Reply-To: Your message of "Fri, 21 Aug 1998 20:50:37 EST." <Pine.HPP.3.95.980821204532.12165B-100000@fohnix.metronet.com>
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> Am I doing something really stupid here or is this a compiler bug?
> The output of this program under 2.2.7-RELEASE is "1.2.3.4 1.2.3.4"
> which isn't what I was expecting. "1.2.3.4 5.6.7.8" is what I was
> hoping for.
>
> #include <stdio.h>
> #include <netinet/in.h>
> #include <netinet/in_systm.h>
> #include <netinet/ip.h>
> #include <arpa/inet.h>
>
> void main() {
> struct ip iph;
>
> iph.ip_src.s_addr = ntohl(0x01020304);
> iph.ip_dst.s_addr = ntohl(0x05060708);
>
> printf("%s %s\n", inet_ntoa(iph.ip_src), inet_ntoa(iph.ip_dst));
> }
inet_ntoa returns a pointer to a static buffer. gcc is evaluating
arguments right to left (ie. in stacking order), so the ip_src call is
made last, but the pointer is the same in both cases. Try:
printf("%s ", inet_ntoa(iph.ip_src));
printf("%s\n", inet_ntoa(iph.ip_dst));
or use strdup() if your real intent is to pass the strings around.
--
\\ Sometimes you're ahead, \\ Mike Smith
\\ sometimes you're behind. \\ mike@smith.net.au
\\ The race is long, and in the \\ msmith@freebsd.org
\\ end it's only with yourself. \\ msmith@cdrom.com
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