From mboxrd@z Thu Jan  1 00:00:00 1970
From: random832@fastmail.com (Random832)
Date: Tue, 19 Sep 2017 13:56:48 -0400
Subject: [TUHS] Happy birthday,
 Dennis Ritchie! [ really sun vs dec/apollo --> X and NeWS ]
In-Reply-To: <20170919135652.GN25650@mcvoy.com>
References: <f05f5fe905a5279e242c1ff265f43c690eb4052e@webmail.yaccman.com>
 <1505782328.3172479.1110519744.63D53ACC@webmail.messagingengine.com>
 <20170919025031.GA25650@mcvoy.com>
 <20170919135359.G38me%steffen@sdaoden.eu>
 <20170919135652.GN25650@mcvoy.com>
Message-ID: <1505843808.1332176.1111446696.14AB97E4@webmail.messagingengine.com>

On Tue, Sep 19, 2017, at 09:56, Larry McVoy wrote:
> On Tue, Sep 19, 2017 at 03:53:59PM +0200, Steffen Nurpmeso wrote:
> >  |void    
> >  |my_perror(char *file, int line, char *msg)
> >  |{
> >  |        char    *p = 0;
> >  |        int     save = errno;
> >  |
> >  |        if (p = getenv("_BK_VERSION")) {
> >  |                if (strneq(p, "bk-", 3)) p += 3;
> >  |                fprintf(stderr, "%s:%d (%s): ", file, line, p);
> >  |} else {
> >  |                fprintf(stderr, "%s:%d: ", file, line);
> >  |}
> >  |        if (p = strerror(errno)) {
> >  |                fprintf(stderr, "%s: %s\n", msg, p);
> >  |} else {
> >  |                fprintf(stderr, "%s: errno=%d\n", msg, errno);
> >  |}
> >  |        errno = save;   
> >  |}
> >  |
> >  |libc should do that.
> > 
> > That really made me wonder why "save" is not used, errno may
> > eventually change along the way.  Ok ok, but.. well.
> 
> Huh?  save is set with errno and then errno is restored to save.   The 
> point of save is to do the library calls (which do syscalls which 
> could in theory change errno) and leave it the same as it was on
> the way in.

I think his point was that you should be passing save (rather than
errno) to the strerror and the last printf, because the preceding
library calls may have changed errno.