which functions set the end-of-file indicator?

[nicolas.sitbon]

Hi everybody, in a french C book, the author says that only {fgetc,
getc, getchar, fgetwc, getwc, getwchar, fgets, gets, fgetws, getws,
fputc, putc, putchar, fputwc, putwc, putwchar, fputs, puts, fputws}
are guaranteed to set the end-of-file indicator when the end-of-file
is reached, but in C99 standard, I find p 288 (ISO/IEC 9899:TC3
Committee Draft — Septermber 7, 2007 WG14/N1256)

/* =============== ============== */
#include <stdio.h>
/* ... */
int count; float quant; char units[21], item[21];
do {
count = fscanf(stdin, "%f%20s of %20s", &quant, units, item);
fscanf(stdin,"% *[^\n]");
} while (!feof(stdin) && !ferror(stdin)) ;
/* =============== ============== */
It seems to say that fscanf family function set end-of-file indicator
too? which functions set the end-of-file indicator?

[Greg Comeau]

In article <g7**********@p anix3.panix.com >,
Greg Comeau <co****@comeauc omputing.comwro te:

>In article <1217878106.929 229@news1nwk>,
Eric Sosman <Er*********@su n.comwrote:

>>... set ... the end-of-file
indicator. putc(), for example, cannot.

Dunno if we're using different words or not, but
putc certainly can return EOF.

Oops, we're definitely using different words,
so while what I wrote is true, you were clearly talking
about something else.
--
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Comeau C/C++ ONLINE == http://www.comeaucomputing.com/tryitout
World Class Compilers: Breathtaking C++, Amazing C99, Fabulous C90.
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[Keith Thompson]

co****@panix.co m (Greg Comeau) writes:

In article <1217878106.929 229@news1nwk>,
Eric Sosman <Er*********@su n.comwrote:

>>... set ... the end-of-file
indicator. putc(), for example, cannot.

Dunno if we're using different words or not, but
putc certainly can return EOF.

Certainly.

Returning EOF and setting the end-of-file indicator are two different
things.

Concretely:

before = feof(stdout);
putc_result = putc('x');
after = feof(stdout);

It can be the case that putc_result == EOF, but it cannot be the case
that before==0 and after!=0.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[CBFalconer]

Greg Comeau wrote:

Eric Sosman <Er*********@su n.comwrote:

>... set ... the end-of-file
indicator. putc(), for example, cannot.

Dunno if we're using different words or not, but
putc certainly can return EOF.

Returning EOF signals error, not setting of end-of-file indicator.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.

[Barry Schwarz]

On Mon, 4 Aug 2008 18:45:02 -0700 (PDT), vi******@gmail. com wrote:

>On Aug 5, 3:40 am, [e-mail] m (Greg Comeau) wrote:

>In article <1217878106.929 229@news1nwk>,
Eric Sosman <Eric.Sos...@su n.comwrote:

>... set ... the end-of-file
indicator. putc(), for example, cannot.

Dunno if we're using different words or not, but
putc certainly can return EOF.

The end of file indicator has nothing to do with the EOF macro.
When putc returns EOF, it means one of the following

o error with the stream; ferror() should return non-zero.
o EOF is a valid byte value that has been written to the stream.

The second case cannot be. EOF is guaranteed to be negative. While
it is certainly possible to pass this value to putc, it will be
converted to unsigned char (7.19.7.8-2 and 7.19.7.3-2). It is this
positive value which will be returned, not EOF.

>
Mr Sosman is talking about file streams that feof() returns non-zero
for. (ie the eof flag is set).
putc cannot set that flag.

--
Remove del for email

[santosh]

Barry Schwarz wrote:

On Mon, 4 Aug 2008 18:45:02 -0700 (PDT), vi******@gmail. com wrote:

>>On Aug 5, 3:40 am, [e-mail] m (Greg Comeau) wrote:

>>In article <1217878106.929 229@news1nwk>,
Eric Sosman <Eric.Sos...@su n.comwrote:

... set ... the end-of-file
indicator. putc(), for example, cannot.

Dunno if we're using different words or not, but
putc certainly can return EOF.

The end of file indicator has nothing to do with the EOF macro.
When putc returns EOF, it means one of the following

o error with the stream; ferror() should return non-zero.
o EOF is a valid byte value that has been written to the stream.

The second case cannot be. EOF is guaranteed to be negative. While
it is certainly possible to pass this value to putc, it will be
converted to unsigned char (7.19.7.8-2 and 7.19.7.3-2). It is this
positive value which will be returned, not EOF.

And here is a test program as well:

#include <stdio.h>
#include <stdlib.h>

int main(void) {
int retval = 0, rc = 0;
puts("Writing EOF to stderr with putc...");
retval = putc(EOF, stderr);
if (retval == EOF) {
printf("\nputc returned EOF. Value is: %d\n", retval);
if (ferror(stderr) ) {
puts("Error indicator for stderr set.");
rc = EXIT_FAILURE;
}
} else printf("\nputc returned: %d\n", retval);
return rc;
}

$ ./a.out
Writing EOF to stderr with putc...
?
putc returned: 255
$

[vippstar]

On Aug 5, 11:44 am, Barry Schwarz <schwa...@dqel. comwrote:

On Mon, 4 Aug 2008 18:45:02 -0700 (PDT), vipps...@gmail. com wrote:

<snip>

The end of file indicator has nothing to do with the EOF macro.
When putc returns EOF, it means one of the following

o error with the stream; ferror() should return non-zero.
o EOF is a valid byte value that has been written to the stream.

The second case cannot be. EOF is guaranteed to be negative. While
it is certainly possible to pass this value to putc, it will be
converted to unsigned char (7.19.7.8-2 and 7.19.7.3-2). It is this
positive value which will be returned, not EOF.

No it can be. We had a recent discussion about this and I think
everyone agreed that it's possible for EOF to be a valid byte.

google thread
<http://groups.google.com/group/comp....thread/thread/
9047fe9cc86e1c6 a/d5b9489e0b16a41 5>
or use the message id
<c9************ *************** *******@e39g200 0hsf.googlegrou ps.com>

[vippstar]

On Aug 5, 12:35 pm, santosh <santosh....@gm ail.comwrote:

Barry Schwarz wrote:

On Mon, 4 Aug 2008 18:45:02 -0700 (PDT), vipps...@gmail. com wrote:

>On Aug 5, 3:40 am, [e-mail] m (Greg Comeau) wrote:
In article <1217878106.929 229@news1nwk>,
Eric Sosman <Eric.Sos...@su n.comwrote:

>... set ... the end-of-file
indicator. putc(), for example, cannot.

>Dunno if we're using different words or not, but
putc certainly can return EOF.

>The end of file indicator has nothing to do with the EOF macro.
When putc returns EOF, it means one of the following

o error with the stream; ferror() should return non-zero.
o EOF is a valid byte value that has been written to the stream.

The second case cannot be. EOF is guaranteed to be negative. While
it is certainly possible to pass this value to putc, it will be
converted to unsigned char (7.19.7.8-2 and 7.19.7.3-2). It is this
positive value which will be returned, not EOF.

And here is a test program as well:

<snip>

Test programs like this are meaningless.
It's like claiming that CHAR_BIT is 8 and then writing a test program
to back up the claim...
See my response to Mr Schwarz about EOF and putc.

[santosh]

vi******@gmail. com wrote:

On Aug 5, 11:44 am, Barry Schwarz <schwa...@dqel. comwrote:

>On Mon, 4 Aug 2008 18:45:02 -0700 (PDT), vipps...@gmail. com wrote:

<snip>

>The end of file indicator has nothing to do with the EOF macro.
When putc returns EOF, it means one of the following

o error with the stream; ferror() should return non-zero.
o EOF is a valid byte value that has been written to the stream.

The second case cannot be. EOF is guaranteed to be negative. While
it is certainly possible to pass this value to putc, it will be
converted to unsigned char (7.19.7.8-2 and 7.19.7.3-2). It is this
positive value which will be returned, not EOF.

No it can be. We had a recent discussion about this and I think
everyone agreed that it's possible for EOF to be a valid byte.

google thread
<http://groups.google.com/group/comp....thread/thread/
9047fe9cc86e1c6 a/d5b9489e0b16a41 5>
or use the message id
<c9************ *************** *******@e39g200 0hsf.googlegrou ps.com>

Are you specifically claiming that a call to fputc/putc with EOF as it's
first argument will return EOF if a call to ferror on the stream
immediately after the fputc/putc call returns zero?

[CBFalconer]

vi******@gmail. com wrote:

>

.... snip ...

>
No it can be. We had a recent discussion about this and I think
everyone agreed that it's possible for EOF to be a valid byte.

Since EOF is a negative constant, it is hard to represent in an
unsigned char.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.

[Richard Heathfield]

CBFalconer said:

vi******@gmail. com wrote:

>>

... snip ...

>>
No it can be. We had a recent discussion about this and I think
everyone agreed that it's possible for EOF to be a valid byte.

Since EOF is a negative constant, it is hard to represent in an
unsigned char.

It is, however, trivial to convert EOF into an unsigned char.

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
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