using write() instead of puts() in a trivial program?

[Charles Ulrich]

Greetings,

I hope my greenness isn't showing too bad by asking this, but I ran across
this trivial program today that left me flabbergasted:

#define MESSAGE "This account is currently not available.\n"

int
main(int argc, char *argv[])
{
write(STDOUT_FI LENO, MESSAGE, sizeof(MESSAGE) );
_exit(1);
}

This is an excerpt from the newly-rewritten nologin(8) in FreeBSD. I am
not willing to accept that the person who committed this code is a fool,
thus I have to conclude that I just don't understand why exactly the
following isn't good enough for such a trivial program:

puts("This account is currently not available.");

Perhaps write() would be appropriate in a program which did intensive
amounts of output, but the meat of this program is literally 1 line long.

I tried doing a Google search, but as you can imagine, the commonality of
the "write" keyword throws off any results that might be useful, so I was
wondering some kind, generous person here could clue me in on what's going
on here. I'd greatly appreciate it.

Charles Ulrich

[Joona I Palaste]

Charles Ulrich <NO***@bloodyse curenym.spamnet > scribbled the following:

Greetings, I hope my greenness isn't showing too bad by asking this, but I ran across
this trivial program today that left me flabbergasted: #define MESSAGE "This account is currently not available.\n" int
main(int argc, char *argv[])
{
write(STDOUT_FI LENO, MESSAGE, sizeof(MESSAGE) );
_exit(1);
} This is an excerpt from the newly-rewritten nologin(8) in FreeBSD. I am
not willing to accept that the person who committed this code is a fool,
thus I have to conclude that I just don't understand why exactly the
following isn't good enough for such a trivial program: puts("This account is currently not available."); Perhaps write() would be appropriate in a program which did intensive
amounts of output, but the meat of this program is literally 1 line long. I tried doing a Google search, but as you can imagine, the commonality of
the "write" keyword throws off any results that might be useful, so I was
wondering some kind, generous person here could clue me in on what's going
on here. I'd greatly appreciate it.

If this is supposed to be a program that, when used for a user's shell,
displays the notice and then terminates, then I have to share your
confusion. Using a simple puts() call instead of a non-standard write()
call, even followed with a non-standard _exit() call, would have been
much simpler. Perhaps you could track down the writer of this program
and ask him why he wrote it that way?

--
/-- Joona Palaste (pa*****@cc.hel sinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"Show me a good mouser and I'll show you a cat with bad breath."
- Garfield

[Alexander Bartolich]

begin followup to Charles Ulrich:

int
main(int argc, char *argv[])
{
write(STDOUT_FI LENO, MESSAGE, sizeof(MESSAGE) );
_exit(1);
}
write(2) is a system call.
_exit(2) is a system call.
[...] I just don't understand why exactly the following isn't
good enough for such a trivial program:

puts("This account is currently not available.");

puts(3) is part of the C run time library.

By using nothing but system calls the total size of the resulting
binary can be minimized. See option -nostdlib of gcc.

--
Für Google, Tux und GPL!

[Tom St Denis]

"Joona I Palaste" <pa*****@cc.hel sinki.fi> wrote in message
news:bt******** **@oravannahka. helsinki.fi...

If this is supposed to be a program that, when used for a user's shell,
displays the notice and then terminates, then I have to share your
confusion. Using a simple puts() call instead of a non-standard write()
call, even followed with a non-standard _exit() call, would have been
much simpler. Perhaps you could track down the writer of this program
and ask him why he wrote it that way?

Probably links in less code? Let's try this out

test1.c
#include <stdio.h>
int main(void) { puts("hello world"); return 0; }

vs.

test2.c
#include <unistd.h>
int main(void) { write(0, "hello world\n", 12); return 0; }

vs.

test3.c
#include <stdio.h>
int main(void) { printf("hello world\n"); return 0; }

All compile and execute fine in Linux... [compiled with -O2 -s]

tombox root # ls -l test?
-rwxr-xr-x 1 root root 3020 Jan 12 15:43 test1
-rwxr-xr-x 1 root root 3040 Jan 12 15:43 test2
-rwxr-xr-x 1 root root 3020 Jan 12 15:46 test3

So it turns out puts/printf is smaller ;-)

I guess the BSD guy either had a really specific reason [e.g. part of the
kernel? not in this case...] since puts is simpler and smaller!

Personally I'd just printf since I use it for all output ;-)

Tom

[Keith Thompson]

Charles Ulrich <NO***@BLOODYse curenym.SPAMnet > writes:

I hope my greenness isn't showing too bad by asking this, but I ran across
this trivial program today that left me flabbergasted:

#define MESSAGE "This account is currently not available.\n"

int
main(int argc, char *argv[])
{
write(STDOUT_FI LENO, MESSAGE, sizeof(MESSAGE) );
_exit(1);
}

This is an excerpt from the newly-rewritten nologin(8) in FreeBSD.

[...]

Presumably the FreeBSD nologin program doesn't need to be portable to
anything other than FreeBSD. Given that constraint, I suppose there's
not much advantage in using the portable puts() rather than the
relatively non-portable write().

Having said that, it's not how I would have written it. puts() or
printf() would make for more legible code.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://www.sdsc.edu/~kst>
Schroedinger does Shakespeare: "To be *and* not to be"

[Peteris Krumins]

Charles Ulrich <NO***@BLOODYse curenym.SPAMnet > wrote in
news:pa******** *************** *****@BLOODYsec urenym.SPAMnet:

Greetings,

I hope my greenness isn't showing too bad by asking this, but I ran
across this trivial program today that left me flabbergasted:

#define MESSAGE "This account is currently not available.\n"

int
main(int argc, char *argv[])
{
write(STDOUT_FI LENO, MESSAGE, sizeof(MESSAGE) );
_exit(1);
}

This is an excerpt from the newly-rewritten nologin(8) in FreeBSD. I
am not willing to accept that the person who committed this code is a
fool, thus I have to conclude that I just don't understand why exactly
the following isn't good enough for such a trivial program:

puts("This account is currently not available.");

Perhaps write() would be appropriate in a program which did intensive
amounts of output, but the meat of this program is literally 1 line
long.

I tried doing a Google search, but as you can imagine, the commonality
of the "write" keyword throws off any results that might be useful, so
I was wondering some kind, generous person here could clue me in on
what's going on here. I'd greatly appreciate it.

Charles Ulrich

Finding an answer to such silly problem is the same as asking and trying
to find an answer to a problem like "I have to go to the shop which is
across a street, I chose to go by bike. Maybe I should have chosen to
go to the shop by my shiny car, my shiny helicopter, my elephant?".
P.Krumins

[Eric Sosman]

Charles Ulrich wrote:

Greetings,

I hope my greenness isn't showing too bad by asking this, but I ran across
this trivial program today that left me flabbergasted:

#define MESSAGE "This account is currently not available.\n"

int
main(int argc, char *argv[])
{
write(STDOUT_FI LENO, MESSAGE, sizeof(MESSAGE) );
_exit(1);
}

This is an excerpt from the newly-rewritten nologin(8) in FreeBSD. I am
not willing to accept that the person who committed this code is a fool,
thus I have to conclude that I just don't understand why exactly the
following isn't good enough for such a trivial program:

puts("This account is currently not available.");

Various people have speculated about the pros and
cons and possible motivations for this code, but no one
yet seems to have mentioned the more interesting aspect:
the code outputs one more character than it (probably)
intends.

If the trailing '\0' is actually required for some
peculiar reason, that's unusual enough that a comment
in the source should be mandatory. If (as seems more
likely) the trailing '\0' is a bug, the code stands as
an object lesson in why stupid optimizations are stupid.

--
Er*********@sun .com

[CBFalconer]

Keith Thompson wrote:

Charles Ulrich <NO***@BLOODYse curenym.SPAMnet > writes:

I hope my greenness isn't showing too bad by asking this, but I
ran across this trivial program today that left me flabbergasted:

#define MESSAGE "This account is currently not available.\n"

int
main(int argc, char *argv[])
{
write(STDOUT_FI LENO, MESSAGE, sizeof(MESSAGE) );
_exit(1);
}

This is an excerpt from the newly-rewritten nologin(8) in FreeBSD.

[...]

Presumably the FreeBSD nologin program doesn't need to be portable
to anything other than FreeBSD. Given that constraint, I suppose
there's not much advantage in using the portable puts() rather than
the relatively non-portable write().

Having said that, it's not how I would have written it. puts() or
printf() would make for more legible code.

This may have to run in circumstances where the C initialization
cannot function, thus making stdout unavailable.

--
Chuck F (cb********@yah oo.com) (cb********@wor ldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net> USE worldnet address!

[Charles Ulrich]

On Mon, 12 Jan 2004 23:09:24 +0000, Peteris Krumins wrote:

Finding an answer to such silly problem is the same as asking and trying
to find an answer to a problem like "I have to go to the shop which is
across a street, I chose to go by bike. Maybe I should have chosen to
go to the shop by my shiny car, my shiny helicopter, my elephant?".
P.Krumins

It's pretty easy to say that in retrospect, isn't it? But look at it from
my point of view. I'm just now emerging from being a complete novice in C
and I stumbled across some code that made little sense given its
elementary job. I am at too low a skill level to be deciding for myself
what constitutes a "silly problem" and what does not. _That's why I asked._

Thanks and gratitude to those who provided helpful input.

Charles Ulrich

[Severian]

On 12 Jan 2004 20:10:59 GMT, Alexander Bartolich
<al************ *****@gmx.at> wrote:

begin followup to Charles Ulrich:

int
main(int argc, char *argv[])
{
write(STDOUT_FI LENO, MESSAGE, sizeof(MESSAGE) );
_exit(1);
}

write(2) is a system call.
_exit(2) is a system call.

[...] I just don't understand why exactly the following isn't
good enough for such a trivial program:

puts("This account is currently not available.");

puts(3) is part of the C run time library.

By using nothing but system calls the total size of the resulting
binary can be minimized. See option -nostdlib of gcc.

Also, when the C standard library is shared, and its file is corrupt
or inaccessible, minimum programs can run.

- Sev