question on fgets

[subramanian100in]

Suppose fgets is used to read a line of input.
char str[1024];
fgets(str, sizeof(str), stdin);
After reading some characters on the same line, if end-of-file is
encountered, will fgets return the 'str' parameter and set EOF
indicator for the stream ? Or will it return the string argument and
set EOF indicator only on subsequent call ?

Kindly clarify

Thanks
V.Subramanian

[santosh]

su************* *@yahoo.com, India wrote:

Suppose fgets is used to read a line of input.
char str[1024];
fgets(str, sizeof(str), stdin);

The parenthesis to sizeof is not required except for types.

After reading some characters on the same line, if end-of-file is
encountered, will fgets return the 'str' parameter and set EOF
indicator for the stream ? Or will it return the string argument and
set EOF indicator only on subsequent call ?

Kindly clarify

If end-of-file is detected after one or more characters have been read,
then fgets will return 'str'. Otherwise it will return a null pointer.

[Jens Thoms Toerring]

su************* *@yahoo.com, India <su************ **@yahoo.comwro te:

Suppose fgets is used to read a line of input.
char str[1024];
fgets(str, sizeof(str), stdin);
After reading some characters on the same line, if end-of-file is
encountered, will fgets return the 'str' parameter and set EOF
indicator for the stream ? Or will it return the string argument and
set EOF indicator only on subsequent call ?

Here's what the C89 standard says about it:

The fgets function returns s if successful. If end-of-file is
encountered and no characters have been read into the array, the
contents of the array remain unchanged and a null pointer is returned.
If a read error occurs during the operation, the array contents are
indeterminate and a null pointer is returned.

So if the last line of the file has no '\n' at the end, 'str'
gets returned (hitting end-of-file isn't an error) and NULL
only on a subsequent call of fgets().

Regards, Jens
--
\ Jens Thoms Toerring ___ [e-mail]
\______________ ____________ http://toerring.de

[CBFalconer]

"su************ **@yahoo.com, India" wrote:

>
Suppose fgets is used to read a line of input.
char str[1024];
fgets(str, sizeof(str), stdin);
After reading some characters on the same line, if end-of-file is
encountered, will fgets return the 'str' parameter and set EOF
indicator for the stream ? Or will it return the string argument
and set EOF indicator only on subsequent call ?

Why ask here? All you have to do is read the C standard, and you
will find the following:

7.19.7.2 The fgets function

Synopsis
[#1]
#include <stdio.h>
char *fgets(char * restrict s, int n,
FILE * restrict stream);

Description

[#2] The fgets function reads at most one less than the
number of characters specified by n from the stream pointed
to by stream into the array pointed to by s. No additional
characters are read after a new-line character (which is
retained) or after end-of-file. A null character is written
immediately after the last character read into the array.

Returns

[#3] The fgets function returns s if successful. If end-of-
file is encountered and no characters have been read into
the array, the contents of the array remain unchanged and a
null pointer is returned. If a read error occurs during the
operation, the array contents are indeterminate and a null
pointer is returned.

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

[Ralf Damaschke]

su************* *@yahoo.com, India wrote:

Suppose fgets is used to read a line of input.
char str[1024];
fgets(str, sizeof(str), stdin);
After reading some characters on the same line, if end-of-file is
encountered, will fgets return the 'str' parameter and set EOF
indicator for the stream ? Or will it return the string argument and
set EOF indicator only on subsequent call ?

After you got three answers that does not address your question I
will give it a try. You already stated in the question that you are
aware that fgets() will return the str parameter (as opposed NULL).(*)

If you thereafter call feof() on this stream it should return true.

7.19.1p2 requires "an end-of-file indicator that records whether
the end of the file has been reached". And by 7.19.10.2p3 "The feof
function returns nonzero if and only if the end-of-file indicator
is set for stream."

(*) I would not expect that fgets returns non-NULL on all systems
for a text file since in text files lines are required to end with
a newline.

-- Ralf

[Richard]

CBFalconer <cb********@yah oo.comwrites:

"su************ **@yahoo.com, India" wrote:

>>
Suppose fgets is used to read a line of input.
char str[1024];
fgets(str, sizeof(str), stdin);
After reading some characters on the same line, if end-of-file is
encountered, will fgets return the 'str' parameter and set EOF
indicator for the stream ? Or will it return the string argument
and set EOF indicator only on subsequent call ?

Why ask here? All you have to do is read the C standard

You will of course, in true pompous and big head fashion, be answering
ALL C questions with this ridiculous bit of c.l.c oneupsmanship I
assume?

[Joe Wright]

Ralf Damaschke wrote:

su************* *@yahoo.com, India wrote:

>Suppose fgets is used to read a line of input.
char str[1024];
fgets(str, sizeof(str), stdin);
After reading some characters on the same line, if end-of-file is
encountered, will fgets return the 'str' parameter and set EOF
indicator for the stream ? Or will it return the string argument and
set EOF indicator only on subsequent call ?

After you got three answers that does not address your question I
will give it a try. You already stated in the question that you are
aware that fgets() will return the str parameter (as opposed NULL).(*)

If you thereafter call feof() on this stream it should return true.

7.19.1p2 requires "an end-of-file indicator that records whether
the end of the file has been reached". And by 7.19.10.2p3 "The feof
function returns nonzero if and only if the end-of-file indicator
is set for stream."

(*) I would not expect that fgets returns non-NULL on all systems
for a text file since in text files lines are required to end with
a newline.

The fgets() function has no such requirement. If the last line of a text
stream has no terminating '\n', so be it. The line in str will be
terminated with '\0' and the eof indicator will be set but str, not NULL
is returned by fgets().

--
Joe Wright
"Everything should be made as simple as possible, but not simpler."
--- Albert Einstein ---

[Antoninus Twink]

On 27 Jul 2008 at 18:26, Richard wrote:

CBFalconer <cb********@yah oo.comwrites:

>Why ask here? All you have to do is read the C standard

You will of course, in true pompous and big head fashion, be answering
ALL C questions with this ridiculous bit of c.l.c oneupsmanship I
assume?

I was pretty impressed that he managed to answer a question about fgets
(albeit very rudely) without spamming about his ridiculous "ggets"
function.

[Richard]

Antoninus Twink <no****@nospam. invalidwrites:

On 27 Jul 2008 at 18:26, Richard wrote:

>CBFalconer <cb********@yah oo.comwrites:

>>Why ask here? All you have to do is read the C standard

You will of course, in true pompous and big head fashion, be answering
ALL C questions with this ridiculous bit of c.l.c oneupsmanship I
assume?

I was pretty impressed that he managed to answer a question about fgets
(albeit very rudely) without spamming about his ridiculous "ggets"
function.

He did that once today already.

[vippstar]

On Jul 27, 3:42 pm, santosh <santosh....@gm ail.comwrote:

subramanian10.. [e-mail], India wrote:

Suppose fgets is used to read a line of input.
char str[1024];
fgets(str, sizeof(str), stdin);

The parenthesis to sizeof is not required except for types.

It is also not required for "types". The parenthesis is required for
the cast.

After reading some characters on the same line, if end-of-file is
encountered, will fgets return the 'str' parameter and set EOF
indicator for the stream ? Or will it return the string argument and
set EOF indicator only on subsequent call ?

Kindly clarify

If end-of-file is detected after one or more characters have been read,
then fgets will return 'str'. Otherwise it will return a null pointer.

Note that in the next read, fgets will return NULL. So it's O.K. to
use fgets like,
while(fgets() != NULL)