[cfe-dev] How can I use the result of a void expression? :p

[Neil Booth]

Keith Bauer wrote:-

> > Yep, that's a bug, but not because ?: has side effects.  It is
> > because that warning should never be emitted for a void expression,
> > patch here:
> > http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-
> > Mon-20070820/001680.html
> 
> I think my patch is still necessary:
> 
> int r(void);
> void foo(int f)
> {
>     f ? r() : r() + r();
> }
> imac:Desktop keith$ gcc -fsyntax-only -Wall -Wextra side-effect-test.c
> imac:Desktop keith$ clang -fsyntax-only side-effect-test.c
> side-effect-test.c:4:5: warning: expression result unused
>     f ? r() : r() + r();
>     ^~~~~~~~~~~~~~~~~~~
> 1 diagnostic generated.
> 
> ( replacing + with , makes more sense but then my patch still isn't
> sufficient ;) )
> 
> Maybe the warning should never be emitted for expressions returning
> void, but that's more of a consequence that a void expression should
> always have a side effect than the underlying reason not to emit the
> warning...

Though it's most likely a separate issue, for the above testcase, 

	f ? r() : r() + r();
	          ~~~ ^ ~~~

"unused operation" would be more appropriate I suspect.

Neil.