return value of fgets()

[Roman Mashak]

Hello, All!

I met a source code where

while ( fgets(buf, sizeof(buf), fp ) != (char*) 0 )

What's the special reason to compare result with 0 (casting to char pointer)
rather than simply with NULL?

With best regards, Roman Mashak. E-mail: mr*@tusur.ru

[Simon Biber]

Roman Mashak wrote:

while ( fgets(buf, sizeof(buf), fp ) != (char*) 0 )

What's the special reason to compare result with 0 (casting to char pointer)
rather than simply with NULL?

There is no reason. This code is silly. Just use NULL.

Also, there is no need for parentheses around buf in `sizeof buf'. Using
parentheses makes one think that it is a type whose size is being
tested, but in this case it is just an object.

--
Simon.

[Keith Thompson]

"Roman Mashak" <mr*@tusur.ru> writes:

I met a source code where

while ( fgets(buf, sizeof(buf), fp ) != (char*) 0 )

What's the special reason to compare result with 0 (casting to char pointer)
rather than simply with NULL?

There's no good reason to use (char*)0 rather than NULL. On the other
hand, the effect is the same; NULL is just (IMHO) simpler and better
style.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Joe Wright]

Roman Mashak wrote:

Hello, All!

I met a source code where

while ( fgets(buf, sizeof(buf), fp ) != (char*) 0 )

What's the special reason to compare result with 0 (casting to char pointer)
rather than simply with NULL?

With best regards, Roman Mashak. E-mail: mr*@tusur.ru

Just bad taste. Assuming there is in scope 'char buf[N];'..

while (fgets(buf, sizeof buf, fp)) {}

...is the Wright way. The forms..

while (fgets(buf, sizeof buf, fp) != NULL) {}

while (fgets(buf, sizeof buf, fp) != 0) {}

...are acceptable of course.

Note that sizeof is an operator, not a function. It's argument is a
object's name or a type. If an object, no parentheses are necessary. If
a type, the Wright way is 'sizeof (long)' with a space before the '(' so
that it doesn't look so much like a function.

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

[Chuck F.]

Roman Mashak wrote:

I met a source code where

while ( fgets(buf, sizeof(buf), fp ) != (char*) 0 )

What's the special reason to compare result with 0 (casting to
char pointer) rather than simply with NULL?

None. It would be clearer with just NULL, or even 0. To my mind
there is no reason for a comparison at all (others will disagree).

while (fgets(buf, sizeof(buf), fp)) {
dostuff();
}

--
A: Because it fouls the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[Keith Thompson]

"Chuck F. " <cb********@yahoo.com> writes:

Roman Mashak wrote:

I met a source code where
while ( fgets(buf, sizeof(buf), fp ) != (char*) 0 )
What's the special reason to compare result with 0 (casting to char
pointer) rather than simply with NULL?

None. It would be clearer with just NULL, or even 0. To my mind
there is no reason for a comparison at all (others will disagree).

while (fgets(buf, sizeof(buf), fp)) {
dostuff();
}

Just to prove that you're right, I prefer an explicit comparison:

while (fgets(buf, sizeof(buf), fp) != NULL) {
dostuff();
}

But of course any C programmer needs to be able to read code using
either convention (and if you're maintaining existing code, you should
probably conform to the existing style unless it's horrendously bad).

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[pete]

Keith Thompson wrote:

"Chuck F. " <cb********@yahoo.com> writes:

Roman Mashak wrote:

I met a source code where
while ( fgets(buf, sizeof(buf), fp ) != (char*) 0 )
What's the special reason to compare result with 0 (casting to char
pointer) rather than simply with NULL?

None. It would be clearer with just NULL, or even 0. To my mind
there is no reason for a comparison at all (others will disagree).

while (fgets(buf, sizeof(buf), fp)) {
dostuff();
}

Just to prove that you're right, I prefer an explicit comparison:

while (fgets(buf, sizeof(buf), fp) != NULL) {
dostuff();
}

There's also:

while (fgets(buf, sizeof buf, fp) == buf) {
dostuff();
}

--
pete