On 01/07/2016 02:19 PM, Joseph Myers wrote:
On Thu, 7 Jan 2016, Marek Polacek wrote:
This PR points out that we issue a wrong warning message when assigning
two pointers when one of them is plain char. In that case, the compiler
currently says that pointer targets differ in signedness. But that is
not correct; char is a separate type from (un)signed char and is not
compatible with either. So we should instead say that the pointer types
are not compatible.
This effectively means that I'm turning a -Wpointer-sign warning into
a -Wincompatible-pointer-types warning. But -Wincompatible-pointer-types
is a warning that is enabled by default and -Wpointer-sign is enabled by
-Wpedantic || -Wall. So with this, we'd be more verbose and would warn
by default on e.g. "unsigned char *p = "foo";." Not sure if that is
desirable at this stage, so I'm leaning towards pushing this patch for
GCC7.
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.
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.)
In my view, Marek's change makes perfect sense because it the most
closely reflects the properties of the type.
Martin
