RE: [avr-gcc-list] Feature request - compiler warning for "if" stmts that do nothing

[Dave Hansen]

From: "Dave Hylands" <address@hidden>
[...]
> > -Wextra?
> >
> > According to the man page:
> >
> >  o   An empty body occurs in an if or else statement.
> >
> > I'd assume this to be warned.
>
> Hey - that's pretty close.
>
> It triggers on the original posters original request:
>
>         if ( condition );
>         {
>                 ... Do something ...
>         }
>
> x.c:8: warning: empty body in an if-statement
>
> And doesn't trigger on my example: if (condition);else{...do
> something...}
>
> It still doesn't warn about while/for loops that are similar:
>
>         while ( conition );
>         {
>                 ... Do something ...
>         }
>
> And
>
>         for (i=0;i<10;i++);
>         {
>                 ... Do something ...
>         }
>
> So it's definitely a step in the right direction.

FWIW...

I use Gimpel's PC-lint (and have for over 15 years).  It has always done a 
very noce job of finding these kinds of problems.

--- begin included file ---
C:\Dave>type mt.c
extern int x;

void foo(void)
{
   int i;

   if (x < 10);
   {
       ++x;
   }

   if (x > 100) ;else
   {
       --x;
   }

   for (i=0; i<10; i++);
   {
       x += x/i;
   }

   while (--i > 5);
   {
       x -= x*i;
   }
}



C:\Dave>lint-nt -u mt.c
PC-lint for C/C++ (NT) Ver. 8.00q, Copyright Gimpel Software 1985-2004

--- Module:   mt.c
             _
   if (x < 10);
mt.c  7  Info 721: Suspicious use of ;
   _
   {
mt.c  8  Warning 548: else expected
                      _
   for (i=0; i<10; i++);
mt.c  17  Info 722: Suspicious use of ;
                 _
   while (--i > 5);
mt.c  22  Info 722: Suspicious use of ;

C:\Dave>
---end included file---

The -u option specifies a "unit" lint, so errors like "x not defined" and 
"foo not called" are suppressed.

Note the first "if" statement generates two warnings because the opening 
brace of the body doesn't have a leading else (which is kind of suspicious 
if you really meant the semicolon.

Also note that there is no message for the "if (x > 100) ;else" line because 
of the space between the parenthesis and the semicolon.  I the colon is 
flush to the paren, the warning is generated.  Indeed, any intervening 
whitespace will suppress the warning on any of the lines.  Warnings can also 
be suppressed by a "lint comment," e.g., "/*lint !e722*/" tells PC-lint to 
suppress warning 722 on this line.

See www.gimpel.com for more info.  A very powerful tool for not a lot of 
money (less than $250), and it works with pretty much any C compiler.

Lint early, lint often.  Lint is your friend.

Regards,
  -=Dave