Re: error: logical && with non-zero constant will always evaluate as true

[Jeff Morriss <jeff.morriss.ws () gmail com>]

Guy Harris wrote:
> On Jan 3, 2013, at 1:40 PM, Jeff Morriss <jeff.morriss.ws () gmail com> wrote:
>
> > Jeff Morriss wrote:
> > > My (Fedora 10) gcc 4.3.2 was also generating this warning; it would seem that a fair spread of gcc versions seem to 
> > > have the problem.
> > > I added a configure check to stop using -Wlogical-op if the compiler is generating this warning in r46916.
> > Interestingly the Ubuntu buildbot says it would also get the warning:
> >
> > > checking whether we can add -Wlogical-op to CFLAGS... yes
> > > checking whether -Wlogical-op generates warnings from strchr()... yes
>
> Which means that
>
>         #include <string.h>
>           
> 	int
>         foo(char *sep, int c)
>         {
>                 if (strchr (sep, c) != NULL)
>                         return 1;
>                 else
>                         return 0;
>         }
>
>         int
>         main(int argc, char **argv)
>         {
>                 return foo(\"<\", 'a');
>         }
>
> fails to compile with the CFLAGS value at the time the test is done, plus -Werror; it could be failing for some other 
> reason.  To quote the comment when I finally got it working for -Wshadow:
>
>         Declare foo() before defining it - if we configure with
>         --enable-extra-gcc-checks, given that we're building with -Werror (so
>         that we find out whether the compiler issues a warning for a particular
>         construct), we have to avoid constructs that will provoke *other*
>         warnings.
>
> so the code in question has to avoid whatever other warnings are being used, and the Ubuntu buildbot builds with --enable-extra-gcc-checks, 
> so it warns about functions not declared with prototypes before they're defined.  I've checked in a change to declare foo() 
> before it's defined; we'll see whether that fixes it.

Lesson to self: don't just be happy when 'configure' spits out the 
expected result.  Instead look at config.log and see *why* I got the 
expected result...  There were a bunch of other warnings in there which 
I didn't get when hand-compiling the program because I wasn't using all 
the options 'configure' was.
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