code

[Bill Cunningham]

I thought I would post this code. It seems to do what I want it to but I
thought I would have it critiqued. I use C89 but I think that maybe some of
the code maybe misplaced. For example, the fopen probably should be under
the strtod's shouldn't it ?

/*code C89 */
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
if (argc != 6) {
puts("print usage error");
exit(EXIT_FAILURE);
}
FILE *fp;
char *error;
double a, b, c, d;
if ((fp = fopen(argv[5], "a")) == NULL)
perror(error);
a = strtod(argv[1], NULL);
b = strtod(argv[2], NULL);
c = strtod(argv[3], NULL);
d = strtod(argv[4], NULL);
fprintf(fp, "%.2f\t%.2f\t%.2f\t%.2f\n", a, b, c, d);
if ((fclose(fp)) == EOF)
perror(error);
return 0;
}

Thanks all.

Bill

[Giorgos Keramidas]

On Wed, 1 Oct 2008 18:40:07 -0400, "Bill Cunningham" <no****@nspam.invalidwrote:

"Barry Schwarz" <sc******@dqel.comwrote in message
news:rn********************************@4ax.com...

>The dismaying thing is this won't generate a diagnostic and you will
spend the next several messages arguing that it is correct.

I don't think so.

What Barry Schwarz wrote *is* true, though.

The following program builds without any diagnostic messages in either
'c89' or 'c99' mode with gcc 4.2.1:

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

3 int
4 main(void)
5 {
6 char *error = '\0';

7 (void)printf("error=%p\n", error);
8 return EXIT_SUCCESS;
9 }

One would probably expect line 6 to issue a diagnostic, but it doesn't.

If line 6 is replaced with

char *error = 1;

then a diagnostic *is* displayed by gcc in both std=c89 and std=c99 mode:

foo.c:7: warning: initialization makes pointer from integer without a cast

It is the special case of an integer that is zero that is, well,
`special'. There is no diagnostic message, and the pointer is
initialized to the system specific value of a null pointer.

[Giorgos Keramidas]

On Thu, 02 Oct 2008 15:45:25 -0700, Nate Eldredge <na**@vulcan.lanwrote:

However, there does seem to be a tradition of implementations
including a few joke error codes in <errno.h>. glibc, notably,
includes EGRATUITOUS, EGREGIOUS, EIEIO, and ED ("The experienced user
will know what is wrong"). FreeBSD is a bit more sedate but does
include EDOOFUS. I have always wanted to find an excuse to use one of
these.

Heh!

Well, EDOOFUS isn't exactly a `joke value', because it is *used* in some
parts of the kernel. In my local version of the 8.0-CURRENT source tree
there are at least the following instances:

keramida@kobe:/usr/src/sys$ fgrep -nr EDOOFUS *
boot/efi/libefi/errno.c:89: errno = EDOOFUS;
dev/hwpmc/hwpmc_mod.c:2439: return EDOOFUS; /* programming error */
dev/md/md.c:1102: error = EDOOFUS;
dev/puc/puc.c:445: return (EDOOFUS);
dev/puc/puc_cfg.c:50: error = EDOOFUS;
geom/bde/g_bde_lock.c:414: return (EDOOFUS); /* Programming error */
geom/part/g_part.c:1332: error = EDOOFUS;
geom/part/g_part.c:1365: error = EDOOFUS; /* Prevent bogus uninit. warning. */
geom/part/g_part.c:1798: error = (arg == (uintptr_t)scheme) ? EDOOFUS : arg;
kern/subr_witness.c:1003: return (EDOOFUS);
sys/errno.h:168:#define EDOOFUS 88 /* Programming error */
keramida@kobe:/usr/src/sys$

Reading through a few cases where EDOOFUS appears, it looks more like a
catch-all value, meaning ``Oops! This wasn't meant to _ever_ happen.
Something looks remarkably screwed up, so let's break out of the kernel
and avoid making a more serious mess of anything.''.

[Flash Gordon]

Giorgos Keramidas wrote, On 04/10/08 04:27:

On Wed, 1 Oct 2008 18:40:07 -0400, "Bill Cunningham" <no****@nspam.invalidwrote:

>"Barry Schwarz" <sc******@dqel.comwrote in message
news:rn********************************@4ax.com.. .

>>The dismaying thing is this won't generate a diagnostic and you will
spend the next several messages arguing that it is correct.

I don't think so.

What Barry Schwarz wrote *is* true, though.

The following program builds without any diagnostic messages in either
'c89' or 'c99' mode with gcc 4.2.1:

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

3 int
4 main(void)
5 {
6 char *error = '\0';

7 (void)printf("error=%p\n", error);
8 return EXIT_SUCCESS;
9 }

One would probably expect line 6 to issue a diagnostic, but it doesn't.

'\0' is just another way of spelling 0. Strange but true.

If line 6 is replaced with

char *error = 1;

then a diagnostic *is* displayed by gcc in both std=c89 and std=c99 mode:

foo.c:7: warning: initialization makes pointer from integer without a cast

That warning is entirely correct. The C standard (all versions) require
a warning.

It is the special case of an integer that is zero that is, well,
`special'. There is no diagnostic message, and the pointer is
initialized to the system specific value of a null pointer.

The special case is specifically an integer *constant* expression that
evaluates to 0, so ((42-42)/42) would also work, and it is guaranteed to
set the pointer to a null pointer whatever than means in terms of bit
patterns. However, the following would not
const int zero = 0;
char *pre = zero;
--
Flash Gordon
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