fflush() on readonly files

[Tim Robbins]

On Sat, Jun 19, 2004 at 02:59:39PM +0400, Andrey Chernov wrote:

> On Sat, Jun 19, 2004 at 11:56:43AM +0200, Radim Kolar wrote:
> > Today I have stepped on another example: advancecomp (in ports):
> > 543      * Get the size of the file.
> > 544      */
> > 545     long fzsize(adv_fz* f)
> > 546     {
> > 547             if (f->type == fz_file) {
> > 548                     struct stat st;
> > 549                     if (fflush(f->f) != 0) {
> > 550                             return -1;
> > 551                     }
> 
> This program relies on undocumented behaviour and should be fixed in 
> anycase. Besides of that the only reasonable approach we can take is to do 
> what majority of systems does here. Since you are interested in the 
> subject, please post specific table for all main systems in the form 
> like:
> 
> System 		readonly fflush() behaviour

This has already been discussed:
- Microsoft libraries and other libraries imitating them discard buffered
  input data (like fpurge().)
- UNIX libc (at least 7th ed.), Solaris libc, GNU libc and products derived
  from P.J. Plauger's C library (e.g. QNX) do nothing and indicate success.
- BSD since Torek's stdio rewrite (inc. FreeBSD and Mac OS X) indicate
  an error.

There is no reason to change from the perfectly correct & well-documented
behaviour BSD has had for 10-15 years. The original poster's example provides
a good argument for this: it detects application bugs.


Tim