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

Ralph Corderoy ralph at inputplus.co.uk
Sun Sep 24 08:24:42 AEST 2017


Hi Larry,

> > > > > 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;   
> > > > > }
>
> I think the reason it works is if it works then errno doesn't change
> and if it doesn't work then we're not going to see the output.

Unless the failure under fprintf(3) is transient?

> So passing save is technically correct but not sure it is practically
> correct.

Passing `save' would also stop readers wondering why it's not being
passed.  :-)

Also, `p = strerror(errno)' is always going to be true;  strerror(3)
doesn't return NULL.  To check for strerror() errors one must errno=0
and then check errno afterwards;  strerror() can kick off LC_MESSAGES
stuff so errors are possible.  Yes, how does one then report that
error...

Another option when in dire straits, e.g. about to _exit() and trying
hard to get *something* to FD 2, is to writev(2) since the iov[] will be
a fixed size and the only formatting issue in the above code is the
`%d' and the space needed by its sprintf(3) can be found at compile
time.

-- 
Cheers, Ralph.
https://plus.google.com/+RalphCorderoy



More information about the TUHS mailing list