Re: getF in lauxlib.c--why call feof?

[Daniel Stephens <daniel@...>]

On OSX my experience doesn't match your explanation, for two reasons...

1) feof doesn't actually do anything that'd cause the EOF flag to get 
set, it just checks the existing flag
2) While the 'condition' isn't permanent, the FLAG is, until you call 
clearerr

In this code, feof is completely unnecessary.

A more thorough implementation might be something along the lines of:

*size = fread(lf->buff, 1, sizeof(lf->buff), lf->f);
if (*size > 0) return lf->buff;
if (feof(lf->f)) {
 /* Do something indicating EOF occurred */
 return NULL;
}
if (ferror(lf->f)) {
 /* Do something indicating error occurred */
}
/* Do something indicating immediate return from read (no error -- was 
lf->buff empty?) */


Daniel.

Edgar Toernig wrote:
> John D. Ramsdell wrote:
>   
> > While almost all of the code was clear to me, I am unable to explain
> > one line of code in getF.  Why is it necessary to call feof before the
> > fread?  Won't fread return 0 if feof returns true?  It seems that
> > fread correctly handles the case of EOF.
> >
> >   if (feof(lf->f)) return NULL;      /* Why? */
> >   *size = fread(lf->buff, 1, sizeof(lf->buff), lf->f);
> >   return (*size > 0) ? lf->buff : NULL;
> >     
>
> It's a precaution to not require excessive "CTRL-D"s when
> reading from a terminal/stdin. (It may also help on not 100%
> correct stdio implementations.)
>
> Contrary to files, an EOF is not a permanent conditions on
> terminal devices: one fread/getc/etc may signal EOF (because
> the user pressed CTRL-D) but the next fread will happily try
> to read more data (and block).
>
> Try "lua -" and count how many "CTRL-D"s are required with
> and without that "if (feof..." line.
>
> Ciao, ET.
>
>