Re: worst.c - foolishness
From: Arthur J. O'Dwyer (ajo_at_nospam.andrew.cmu.edu)
Date: 01/13/04
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Date: Tue, 13 Jan 2004 14:55:09 -0500 (EST)
On Tue, 13 Jan 2004, Jarno A Wuolijoki wrote:
>
> On Mon, 12 Jan 2004, Arthur J. O'Dwyer wrote:
>
> > > char *fmt = "%d, %l";
> >
> > These two lines should probably be combined. Note the subtle change
> > in the indentation, also.
> > char *fmt = "%d, %l", c;
>
> ITYM
> char* fmt = "%d, %l", c;
My mistake. ;-)
> It would be better though if c was somehow used as if it were a
> char* instead. Otherwise it just adds up to obfuscation.
I think you'd have trouble avoiding a compiler warning in that case.
> > > unsigned int z;
> > > while (!feof()) {
> > Surely you meant
> > while (!feof(stdin)) {
> > This will avoid the warnings from those so-called "smarter" compilers. :)
>
> Dunno, it's one bug less if you ignore the misdefinition..
How so? My change merely replaces "undefined behavior upon calling
unprototyped function with wrong arguments" (which Chuck already had
elsewhere) with "undefined behavior upon passing NULL to feof()". Plus,
my bug is much subtler.
> > > if (EOF == c) continue;
> > > }
> >
> > You're missing a
> > scanf("%d", z);
> > here.
> >
> > > gets(&c);
>
> My linker warns about gets so I'd fuse these two into one scanf. You
> can use c as if it was a pointer there too.
Doesn't that remove the bug, though? scanf("%d%s", z, &c) will
most likely try to store a string in the memory pointed to by &c
(invoking undefined behavior on buffer overrun); but the bug I was
trying to introduce there was that
scanf("%d", &foo);
gets(bar);
will store a number in 'foo', and then, assuming the user has pressed
'Return' to end that line of input, will proceed to read and discard
a single newline. OTOH, the gets() doesn't actually have a bug then;
it will store only a single '\0', won't it? So maybe keep that gets(),
but introduce the
scanf("%d", &foo);
fgets(&c, sizeof &c, stdin);
bug(s) elsewhere in the code. [Bugs include lack of prototype for
fgets, causing undefined behavior when passing literal 0 as third
argument; mis#defined 'stdin' that causes the literal 0 in the first
place; passing NULL to fgets in the first place; buffer overflow;
abuse of the 'sizeof' operator; lack of error-checking on scanf;
and the above-mentioned mishandling of possible newline characters
in the input.]
> #define EOF -1
> #define stdin 0
> #define swap(__a, __b) (__a ^= __b ^= __a ^= __b)
>
> char* strfmt = "%d, %l", strtmp;
>
> main()
> {
> int x, y;
> char c;
> unsigned z, zz;
>
> while (feof()==EOF) {
I think the use of == for != is too blatant a mistake. But it
occurs to me that we haven't misused De Morgan's Rule yet; we need
something along the lines of
while (feof()!=EOF || c=(int)getchar() != EOF) {
[I like my cast better than yours. Yours is only designed to
placate the compiler, AFAICT; mine has the "good" intention of
making sure the result of getchar() is wide enough to hold 'EOF'
before assignment to c. ;-) ]
> c = (char) getchar();
> if (c<0) continue;
> }
> scanf("%d%s", z, strtmp);
> printf(strfmt, strtmp, x);
> fflush(stdin);
> for (z = sizeof strfmt; z>=0; z--) for (zz = z; z>=0; zz--);
> if (strfmt[z]-strfmt[zz] <= 0) swap(strfmt[z], strfmt[zz]);
> strfmt = (char*) malloc(123);
> (void) realloc(&strfmt, 245);
> y = strfmt[1000];
> if (z>0) return -1;
> else return main(42.7f);
> }
Finally, it occurs to me that we haven't abused 'goto' yet, nor
attempted to 'switch' on some inappropriate type. Nor even inserted
anywhere an
if (strfmt == "foo")
;-)
-Arthur
[Disclaimer: THIS WHOLE THREAD IS A JOKE. THIS IS INTENTIONALLY
BAD CODE. WE KNOW IT DOES NOT WORK. :) ]
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