[Bug c++/20019] incorrect overflow warning

["neil at daikokuya dot co dot uk" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From neil at daikokuya dot co dot uk  2005-02-17 15:12 -------
Subject: Re:  incorrect overflow warning

schlie at comcast dot net wrote:-

> 
> ------- Additional Comments From schlie at comcast dot net  2005-02-17 14:33 -------
> (In reply to comment #8)
> > char x = 0x80; warning: value changes sign during integer type conversion
> 
> Implying an analogous warning for all assignments between dissimilarly
> signed variables (i.e. signed x; unsigned y; x = y;) which I believe are
> considered "compatible"; and half of all unsigned hex constants being
> assigned to signed types even if cast, as it's arguably the cast which
> produces the virtual numerical over/underflow.
> 
> (where although you're numerically correct, seems like a lot of noise?)

Well it's certainly a matter of taste.  char is arguably a special
case as you cannot assign a value with the high bit set without
creating the warning on some targets.  But if you are assigning
values with the high bit set then arguably you have in mind whether
you are dealing with signed or unsigned values and should be explicit
about signedness.  As such like any warning it tends to expose sloppy
thinking.

Your x=y example is of course not the same; whether a value is
changing sign or not is not knowable at compile time and probably
rarely the case, so I agree complaining about that would be annoying.

Some people have in the past requested command-line switches to
generate warnings for any implicit integer conversion.  I agree a
singed <-> unsigned should not be on by default, though potentially
narrowing conversions are debatably more appropriate to have on by
default.

Neil.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20019