[TUHS] Happy birthday, Dennis Ritchie! [ really sun vs dec/apollo --> X and NeWS ]

[random832@fastmail.com (Random832)]

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.