mutex failing (stupid C++!)

[Kaz Kylheku]

gcc-help-owner@gcc.gnu.org wrote:
> Arggg .. C++ is such a mess.. look at this and spot the bug:
> 
>   {
>     flx_mutex_locker_t (*ehd->spawner_lock);
>     fprintf(stderr,"Thread %p acquired mutex\n", pthread_self());    
>     *ehd->spawner_flag=true; ehd->spawner_cond->broadcast();
>     fprintf(stderr,"Thread %p releasing mutex\n", pthread_self());   }
> 
> This baffled me for 3 days now. The code is legal, it just
> doesn't do what I expected. The fix is ONE CHARACTER.

This should be diagnosed by -Wunused, IMHO. You are calling a
constructor, but ignoring the return value.

Let's look at it this way: if you write:

  2 + 2;

into the program, -Wunused will give you a diagnostic. But if you
construct an object and ignore the result, you don't get a diagnostic.

What's the difference? The expression 2 + 2 is a constructor for 4.