[Bug c++/87292] Warnings with Bit Fields
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87292 Eric Gallager changed: What|Removed |Added See Also||https://gcc.gnu.org/bugzill ||a/show_bug.cgi?id=39170 --- Comment #7 from Eric Gallager --- Besides bug 61414 this bug also reminds me of bug 39170
[Bug c++/87292] Warnings with Bit Fields
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87292
Jonathan Wakely changed:
What|Removed |Added
Status|UNCONFIRMED |NEW
Last reconfirmed||2018-09-13
Ever confirmed|0 |1
--- Comment #6 from Jonathan Wakely ---
(In reply to Nuno Gonçalves from comment #4)
> I found that the issue with enum have been extensively debated at #61414.
> Sorry.
Yes, we already have Bug 61414 for that.
> So actually this bug report is only regarding the warning with initializer
> list:
>
> struct{
> uint8_t c1:6;
> uint8_t c2:6;
> } a;
> auto c = {a.c1, a.c2}; //warning: narrowing conversion of '(unsigned
> char)c1' from 'unsigned char' to 'unsigned char:6' [-Wnarrowing]
Confirmed. The initializers should be promoted before deciding the type of the
std::initializer_list.
This should compile:
#include
struct {
int c1 : 6;
int c2 : 6;
} a;
auto c = { a.c1, a.c2 };
std::initializer_list& r = c;
n.cc:7:14: warning: narrowing conversion of '(int)a.::c1' from
'int' to 'signed char:6' [-Wnarrowing]
7 | auto c = { a.c1, a.c2 };
|~~^~
n.cc:7:14: warning: narrowing conversion of 'a.::c1' from 'int'
to 'signed char:6' [-Wnarrowing]
n.cc:7:20: warning: narrowing conversion of '(int)a.::c2' from
'int' to 'signed char:6' [-Wnarrowing]
7 | auto c = { a.c1, a.c2 };
| ~~^~
n.cc:7:20: warning: narrowing conversion of 'a.::c2' from 'int'
to 'signed char:6' [-Wnarrowing]
n.cc:8:33: error: invalid initialization of reference of type
'std::initializer_list&' from expression of type
'std::initializer_list'
8 | std::initializer_list& r = c;
|
[Bug c++/87292] Warnings with Bit Fields
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87292 --- Comment #5 from Jonathan Wakely --- (In reply to Andrew Pinski from comment #1) > I think the second is correct but I dont know the exact rules about enum > classes; are they unsigned by default? No, the default underlying type is 'int'
[Bug c++/87292] Warnings with Bit Fields
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87292
--- Comment #4 from Nuno Gonçalves ---
I found that the issue with enum have been extensively debated at #61414.
Sorry.
So actually this bug report is only regarding the warning with initializer
list:
struct{
uint8_t c1:6;
uint8_t c2:6;
} a;
auto c = {a.c1, a.c2}; //warning: narrowing conversion of '(unsigned
char)c1' from 'unsigned char' to 'unsigned char:6' [-Wnarrowing]
[Bug c++/87292] Warnings with Bit Fields
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87292
--- Comment #3 from Nuno Gonçalves ---
Also to add, this could be suppressed if
enum class Bool : bool{False=0, True=1};
So a better example is for a 2 bit BitField:
enum class Nr : uint8_t{Zero=0, One=1, Two=2, Three=3};
struct{
Nr v:2;
} b;
[Bug c++/87292] Warnings with Bit Fields
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87292
--- Comment #2 from Nuno Gonçalves ---
Not the case since, same warning if:
enum class Bool : uint8_t {False=0, True=1}
[Bug c++/87292] Warnings with Bit Fields
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87292 --- Comment #1 from Andrew Pinski --- I think the second is correct but I dont know the exact rules about enum classes; are they unsigned by default? I know normal emuns are signed by default.
