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- Subject: Re: getF in lauxlib.c--why call feof?
- From: David Jones <drj@...>
- Date: Sun, 30 Mar 2008 12:59:56 +0100
On 26 Mar 2008, at 20:51, Edgar Toernig wrote:
Luiz Henrique de Figueiredo wrote:
/* EOF flag checked here because when lf->f is a terminal, the fread
may return > 0 even when it is set. If you call fread again and
lf->f is a terminal it will wait for the next line or CTRL-D. */
Actually I think the exact problem is a little different: fread can
return > 0 *and* set the EOF flag. The next time getF is called, if
you call fread, then the terminal will wait for user input. By
feof before fread, you avoid this wait.
* Trying to read past EOF or after an error exposes implemen-
* tation and device (file/tty) differences. Better not ...
if (feof(lf->f) || ferror(lf->f))
Perhaps with an additional note that this is only necessary for
implementations of fread that violate the C standard:
ISO 9899:1999 Section 188.8.131.52 (fgetc):
"If the end-of-file indicator for the stream is set, or if the stream
is at end-of-file, the end-
of-file indicator for the stream is set and the fgetc function
(and fread is documented as working as if it calls fgetc many times).
This violation (in general that successive reads from a terminal only
return EOF once) is a traditional Unix behaviour and there may be
many, older, Unix programs that rely on it. Which is perhaps why
Linux implements it like it does.