Bruno Haible <[EMAIL PROTECTED]> wrote: > Jim Meyering wrote: >> On this subject, I'm nearly convinced that we need printf and fprintf >> wrappers that call fseterr when necessary. That would be cleaner and >> more maintainable than doing s/printf/xprintf/ everywhere. > > I disagree. When you call fseterr, you lose information about the origin > of the error. It will have the effect to produce an error > > error writing /tmp/foobar > > instead of > > out of memory > > thus leading the user's search for the origin and a recovery of the action > in a totally wrong direction.
I see your point, but just saying "out of memory" provides no clue as to which output file may have just been corrupted as a result of this failure. Nor does it mention that the error arose during an attempt at formatted output. I'll bet we have enough of the pieces to write *printf wrappers, that *do* record errno per stream. Of course, such a stream-to-errno mapping would have to be separate from the streams themselves, but that wouldn't be too hard. It would be a lot like gnulib's fchdir emulation. An alternative would be to emit a diagnostic *and* to set the error indicator, but not to exit. The down-side there is that you'd get two diagnostics: one for ENOMEM, and another, later, telling about the write error, possibly with a file name. > Transparency of operation and accurate error messages are two major advantages > of GNU programs over closed-source programs (on average). I'm actually > surprised: Why do the GNU standards not specify that error messages should > be accurate and not misleading? > > Given that there's no room for storing an errno value portably in a FILE > stream, this problem appears unfixable to me. See above :-) > For this reason, I also don't see a point in trying to change ISO C so that > ENOMEM, EILSEQ, or EINVAL situations in fprintf() set the stream's error > indicator. This would lead to inappropriate error messages. Unless they add > an error number field to FILE and provide ferrno() and fseterrno() functions, > of course. Yes, I do see the futility of that, now.
