Re: C PATCH to rectify warning for character types (PR c/23087)

[Joseph Myers <joseph@codesourcery.com>]

On Fri, 8 Jan 2016, Martin Sebor wrote:

> > I don't think it's desirable to raise the warning for this case under
> > different conditions from the warning for other signedness cases.  The
> > targets do differ in signedness - it's just that the difference is between
> > "plain" and "signed" or "plain" and "unsigned", not between signed and
> > unsigned.
> 
> I'm sorry Joseph but I don't quite follow this argument.  Plain
> char is neither a signed [integer] type nor an unsigned [integer]
> type, so it can never differ in signedness from any other type.

Signedness of char (and of bit-fields) is a tristate, "signed", "unsigned" 
and "".  My claim is that a difference between any two of those three 
values is essentially the same kind of difference.  And so at most the 
wording should be adjusted (or maybe an inform ("%<char%> and %<signed 
char%> are different types" added), not the conditions for some such 
warning to be given.

> It seems to me that by the interpretation you suggest, converting
> a signed int* to unsigned long* should be controlled by -Wpointer-
> sign when int and long have the same representation, and by
> -Wincompatible-pointer-types otherwise.  (Which is not what GCC
> does.)

No, because those differ between "int" and "long", not between "signed" 
and "" or "unsigned" and "" as signedness.

-- 
Joseph S. Myers
joseph@codesourcery.com