Re: GCC 3.3.1, new warnings with <limits>

> Hi,
>
> I think that this is a FreeBSD issue.  I compiled
> the same file under Linux, with a GCC 3.3.1 checked out on 7/11
> and did not encounter this warning.
>

I think you hit it on the head.

> I looked in the source code of gcc and found this:
> /usr/src/contrib/gcc/c-common.c
>
>    2597             case LT_EXPR:
>    2598               if (extra_warnings && !in_system_header
>    2599                   && ! (TREE_CODE (primop0) == INTEGER_CST
>    2600                         && ! TREE_OVERFLOW (convert  
> (c_common_signed_typ
> e (type),
>    2601                                                       
> primop0))))
>    2602                 warning ("comparison of unsigned expression <  
> 0 is alway
> s false");
>    2603               value = boolean_false_node;
>    2604               break;
>
>
>
>
> I am guessing that the C preprocessor does not think that it is
> in a system header, and thus prints out the warning.
>
> If I take the following preprocessed source (test.ii) and compile it
> under FreeBSD with g++ -W -c test.ii:
>
> ======================================================================= 
> ========
> # 1 "test.cc"
> # 1 "<built-in>"
> # 1 "<command line>"
> # 1 "test.cc"
> # 1 "/usr/include/c++/3.3/iostream" 1 3
> # 43 "/usr/include/c++/3.3/iostream" 3
>
> static const int digits = (sizeof(unsigned int) * 8 - ((unsigned  
> int)(-1) < 0));
>
> ======================================================================= 
> ========
>
> I get:
>
> In file included from test.cc:1:
> /usr/include/c++/3.3/iostream:44: warning: comparison of unsigned  
> expression <
>    0 is always false
>
>
>
>
>
> If I compile the same file on my Linux box, with a gcc checked out
> from the FSF CVS repository (gcc version 3.3.1 20030711 (prerelease)),
> I do not get the warning.
>
> I am not an expert on the GNU C preprocessor format, but I changed
> two of the lines in the above file to:
>
> # 1 "/usr/include/c++/3.3/iostream" 1
> # 43 "/usr/include/c++/3.3/iostream"
>
> and when I recompiled it under Linux, I also got the warning:
>
> In file included from test.cc:1:
> /usr/include/c++/3.3/iostream:44: warning: comparison of unsigned  
> expression <
>    0 is always false
>
>
>
> Any GCC/FreeBSD expert care to comment? ;)
>
> -- 
> Craig Rodrigues
> http://crodrigues.org
> rodrigc_at_crodrigues.org