[Bug c++/92158] Enum warning when -1 enum converted to unsigned int or int
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92158
Jonathan Wakely changed:
What|Removed |Added
Status|WAITING |NEW
--- Comment #5 from Jonathan Wakely ---
Thank you for the corrected testcase, although compiling with -Werror when
asking for warnings is not very helpful (it obscures what's a warning and
what's an error) and posting code that doesn't even compile is not very helpful
either.
Confirming as a diagnostic enhancement for the following testcase:
enum E { a = -1 } ;
unsigned i = a;
Clang warns with -Wsign-conversion (not enabled by -Wall or -Wextra):
e.cc:2:14: warning: implicit conversion changes signedness: 'E' to 'unsigned
int' [-Wsign-conversion]
unsigned i = a;
~ ^
1 warning generated.
[Bug c++/92158] Enum warning when -1 enum converted to unsigned int or int
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92158
--- Comment #4 from Jonny Grant ---
Hello
Implicit conversion can introduce bugs. I would like to detect implicit enum
conversions to other types in C and C++. How about just adding the C++ warnings
first to match clang in example below?
The following example does produce warnings in C++ with Clang trunk, but not C.
Likewise with MSVC, C++ warning, but no C warning.
G++ only warns on line (19), clang has the additional line (15) and line (17)
warnings.
Could G++ also add the additions warnings?
-O2 -Wall -Wextra -Wconversion -Werror
#include
typedef enum
{
a = -1
} a_t;
a_t f()
{
return a;
}
int main()
{
unsigned int b = f();
a_t test = b;
printf("%u %u", test, b);
return b;
}
#1 with x86-64 clang (trunk)
:15:22: error: implicit conversion changes signedness: 'a_t' to
'unsigned int' [-Werror,-Wsign-conversion]
unsigned int b = f();
~ ^~~
:17:9: error: cannot initialize a variable of type 'a_t' with an lvalue
of type 'unsigned int'
a_t test = b;
^ ~
:19:12: error: implicit conversion changes signedness: 'unsigned int'
to 'int' [-Werror,-Wsign-conversion]
return b;
~~ ^
3 errors generated.
Compiler returned: 1
#1 with x64 msvc v19.22
example.cpp
(18): error C2440: 'initializing': cannot convert from 'unsigned int'
to 'a_t'
(18): note: Conversion to enumeration type requires an explicit cast
(static_cast, C-style cast or function-style cast)
Compiler returned: 2
x86-64 gcc (trunk) - 484ms
#1 with x86-64 gcc (trunk)
: In function 'int main()':
:17:16: error: invalid conversion from 'unsigned int' to 'a_t'
[-fpermissive]
17 | a_t test = b;
|^
||
|unsigned int
Compiler returned: 1
[Bug c++/92158] Enum warning when -1 enum converted to unsigned int or int
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92158 Jonathan Wakely changed: What|Removed |Added Status|UNCONFIRMED |WAITING Last reconfirmed||2019-10-21 Ever confirmed|0 |1 --- Comment #3 from Jonathan Wakely --- Your example doesn't warn with Clang or Clang++ either.
[Bug c++/92158] Enum warning when -1 enum converted to unsigned int or int
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92158 --- Comment #2 from Jonathan Wakely --- At least when the sign doesn't change, i.e. for conversion to int. Please clarify what exactly you want a warning to do.
[Bug c++/92158] Enum warning when -1 enum converted to unsigned int or int
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92158 --- Comment #1 from Jonathan Wakely --- Converting to integral types is a feature of enums, I see no reason to warn.
[Bug c++/92158] Enum warning when -1 enum converted to unsigned int or int
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92158 Richard Biener changed: What|Removed |Added Keywords||diagnostic Version|unknown |10.0 Severity|normal |enhancement
