RFC: GCC should warn when evaluating a pointer return type from a function used in a conditional that performs arithmetic with it

[Darryl L. Miles]

Subject: RFC: GCC should warn when evaluating a pointer return type from 
a function used in a conditional that performs arithmetic with it


Shouldn't GCC generate some form of warning with the following code, for 
the "if(foobar(i) < 0)" statement ?

It does generate a warning if you use "int j = foobar(i);"

I would think this sort of error should be a default warning (i.e. not 
need to specifying any additional -W option) and it should certainly be 
caught when specifying "-Wall".

Tried with:

gcc version 3.4.2 20041017 (Red Hat 3.4.2-6.fc3)
gcc version 4.0.2 20051125 (Red Hat 4.0.2-8)
gcc version 4.2.1



I don't think MSVC warns but SunPro C compiler (with Solaris 10 / Sun 
Studio 12) does.

Request for comments,

Darryl


#include <stdio.h>

extern char *foobar(int a);

char *
foobar(int a)
{
        static char buf[128+1];
        sprintf(buf, "%d", a);
        return buf;
}

int
main(int argc, char *argv[])
{
        char *cp;
        int i;

        i = 42;
        /* vvv SHOULDNT THIS GENERATE SOME FORM OF WARNING ??? */
        if(foobar(i) < 0) {
                printf("TRUE\n");
        } else {
                printf("FALSE\n");
        }

        return 0;
}