24 Sep
2017
24 Sep
'17
12:24 a.m.
Hi Larry,
Unless the failure under fprintf(3) is transient?
> > >
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. 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