Re: [PATCH 1/4] error: save and restore errno
On Tue, Nov 18, 2014 at 05:43:44PM -0800, Jonathan Nieder wrote:
Show 24 quoted lines
> Jeff King wrote:
>
> > It's common to use error() to return from a function, like:
> >
> > if (open(...) < 0)
> > return error("open failed");
> >
> > Unfortunately this may clobber the errno from the open()
> > call. So we often end up with code like this:
> >
> > if (open(...) < 0) {
> > int saved_errno = errno;
> > error("open failed");
> > errno = saved_errno;
> > return -1;
> > }
> >
> > which is less nice.
>
> What the above doesn't explain is why the caller cares about errno.
> Are they going to print another message with strerror(errno)? Or are
> they going to consider some errors non-errors (like ENOENT when trying
> to unlink a file), in which case why is printing a message to stderr
> okay?I guess the unsaid bit is:
Unfortunately this may clobber the errno from the open() call. Even
though error() sees the correct errno, the caller to which we are
returning may see a bogus errno value.
-Peff
Jeff King <peff@peff.net>