[Bug c++/57164] New: enumerator value -1 is too large for underlying type ‘unsigned int’

[vvnic.holas at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57164

 Bug #: 57164
   Summary: enumerator value -1 is too large for underlying type
‘unsigned int’
Classification: Unclassified
   Product: gcc
   Version: 4.8.0
Status: UNCONFIRMED
  Severity: minor
  Priority: P3
 Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: vvnic.ho...@gmail.com


Having an enumerator with a negative value in an enumeration with an unsigned
underlying type produces a compilation error.

enum A : unsigned {
B = -1
};

nicholas@ubuntu:~$ g++ test.cpp -std=c++11
test.cpp:2:7: error: enumerator value -1 is too large for underlying type
‘unsigned int’
  B = -1
   ^

Same error if any other unsigned type is used, or if a scoped enumeration is
used.

As per §7.2.5: "If the underlying type is fixed, the type of each enumerator
prior to the closing brace is the underlying type and the constant-expression
in the enumerator-definition shall be a _converted constant expression_ of the
underlying type (5.19)" (emphasis added)

As per §5.19.3: "A converted constant expression of type T is an expression,
implicitly converted to a prvalue of type T, where the converted expression is
a core constant expression and the implicit conversion sequence contains only
user-defined conversions, lvalue-to-rvalue conversions (4.1), integral
promotions (4.5), and _integral conversions_ (4.7) other than narrowing
conversions (8.5.4)." (emphasis added)

As per §4.7.2 "If the destination type is unsigned, the resulting value is the
least unsigned integer congruent to the source integer"

In other words, the above snippet should be equivalent to:

enum A : unsigned {
B = 4294967295
};

[Bug c++/57164] enumerator value -1 is too large for underlying type ‘unsigned int’

[vvnic.holas at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57164



--- Comment #1 from Nicholas  2013-05-03 21:24:03 
UTC ---

(assuming 32-bit ints and two's complement)

[Bug c++/57170] New: No diagnostic for a negative case when switching over unsigned

[vvnic.holas at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57170



 Bug #: 57170

   Summary: No diagnostic for a negative case when switching over

unsigned

Classification: Unclassified

   Product: gcc

   Version: 4.8.0

Status: UNCONFIRMED

  Severity: normal

  Priority: P3

 Component: c++

AssignedTo: unassig...@gcc.gnu.org

ReportedBy: vvnic.ho...@gmail.com





A signed->unsigned conversion is narrowing, so -1 is not a converted constant

expression. However, the following emits no warning with -Wall, with or without

-std=c++11:



int main() {

unsigned a = 10;

switch (a) {

case -1:

break;

}

return 0;

}



But replacing "unsigned" with any smaller unsigned type (unsigned char or

unsigned short) yields the following warning:



test.cpp:4:9: warning: case label value is less than minimum value for type

[enabled by default]

   case -1:

[Bug c++/58126] New: No diagnostic when inheriting an uninitialized const or reference member

[vvnic.holas at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58126

Bug ID: 58126
   Summary: No diagnostic when inheriting an uninitialized const
or reference member
   Product: gcc
   Version: 4.8.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: vvnic.holas at gmail dot com

The following code compiles without any warning or error:

struct A {
const int value1;
int& value2;
};

struct B : A {};

int main() {
B b; // no error
//A a; // error, as expected
}