Re: gcc doesn't warn that (unsigned > 0) is always true

[David Calinski <neodave at gmx dot net>]

On Mon, 20 Oct 2003 12:12:08 -0400
Daniel Jacobowitz <drow@mvista.com> wrote:

> On Mon, Oct 20, 2003 at 06:09:55PM +0200, David Calinski wrote:
> > Hi all,
> > 
> > This may be a bit stupid, but as I run into problem once because of
> > this...
> > I think gcc should warn about it when "-Wall" is set.
> > 
> > Consider the following snip of code:
> > 
> > 
> > /* gcc (3.3.2 with -Wall and -pedantic)
> >  * doesn't warn that (unsigned > 0) is always true.
> >  */
> > 
> > #include <stdio.h>
> > 
> > void a_loop (unsigned int in) {
> >   int dumb = 0;
> >   do {
> >     ++dumb; /* anything here */
> > 
> >     /* Well, a lot of code can be here,
> >      * almost all variables int _signed_,
> >      * so a programmer may overlook that 'in' is_unsigned_  
> >      */
> >   } while (--in > 0);
> > 
> >   /* variable 'in' will be NEVER less than zero (it's unsigned),
> >    * this is in fact an *endless* loop.
> >    * It should be obvious that it wasn't programmer intention.
> >    * Shouldn't gcc with -Wall warn about it?             
> >    * Shouldn't gcc warn about all such obviously mistaken checks
> >    * (unsigned > 0) that are always true?
> >    */
> > }
> 
> That is not an endless loop.  in == 0 will terminate it.


Right, sorry, my mistake. But it originally was while(--in >= 0), I
just have experimented with it and posted the wrong code. *ashamed*

unsigned int in = 0;
do {
	/* anything */
} while (--in >= 0);

is and endless loop and gcc doesn't warn about it.


-- 
David Calinski