unsigned comparisoms problem?

[Andrew Chittenden]

The following code is a cut down example of a real program. It compares
unsigned values with <= 0 and yet I don't get a warning. Comparing
with < 0 does give me a warning. I've compiled with -Wall -W. I
cannot find any other option that might give me a warning in this case.
Please can the compiler be enhanced to provide warnings in this case: an
extra option will do if existing functionality shouldn't be broken. There
must be lots of code that would benefit from such a check.

--- begin cut here

#include <stdio.h>

unsigned int bigger = 0x26467b5;
unsigned int smaller = 0x26464f5;

int
f(unsigned int p_smaller, unsigned int p_bigger)
{
    int skip = p_smaller - p_bigger;
    if ((p_smaller - p_bigger) <= 0) {
        printf("smaller %d\n", skip);
    } else {
        printf("bigger %d\n", skip);
    }
    if (p_smaller <= 0) {
        printf("smaller is -ve\n");
    } else {
        printf("smaller is +ve\n");
    }
    return skip;
}

int
main()
{
    return f(smaller, bigger);
}

--- end cut here

-- 
Rgds, Andy Chittenden

Email:	achitten@madge.com	Fax:	+44 1753 661011
Multimedia Development, Madge Networks Ltd
Wexham Springs, Framewood Road, Wexham, Slough SL3 6PJ, England