Re: Help with bit-field semantics in C and C++

[Mike Stump <mrs at apple dot com>]

On Tuesday, August 24, 2004, at 12:32  PM, Gabriel Dos Reis wrote:

> Mike Stump <mrs@apple.com> writes:
>
> | On Tuesday, August 24, 2004, at 10:51  AM, Joe Buck wrote:
> | > On Tue, Aug 24, 2004 at 11:05:41AM -0600, Roger Sayle wrote:
> | >> The problem here is that a C++ enum can hold values outside the 
> range
> | >> of it's type.
> |
> | > If it does, the program is not a valid ISO C++ program.
> |
> | ?  What?  Of course it is.
> |
> | I think the standard is perfectly clear in this area:
>
> You're quoting C99 which has a quite different semantics in this area.
> Joe is talking about C++.

While C++ is a times slightly different from C...  It isn't all that 
different:

7 A value of integral type can be explicitly converted to an enumeration
  type.  The value is unchanged if the  integral  value  is  within  the
  range  of the enumeration values (_dcl.enum_).  Otherwise, the result-
  ing enumeration value is unspecified.

4 Each enumeration defines a type  that  is  different  from  all  other
  types.  Following the closing brace of an enum-specifier, each enumer-
  ator has the type of its enumeration.  Prior to the closing brace, the
  type  of each enumerator is the type of its initializing value.  If an
  initializer is specified for an enumerator, the initializing value has
  the  same  type as the expression.  If no initializer is specified for
  the first enumerator, the type is an unspecified integral type.   Oth-
  erwise  the  type is the same as the type of the initializing value of
  the preceding enumerator unless the incremented value  is  not  repre-
  sentable  in that type, in which case the type is an unspecified inte-
  gral type sufficient to contain the incremented value.

5 The underlying type of an enumeration is an  integral  type  that  can
  represent all the enumerator values defined in the enumeration.  It is
  implementation-defined which integral type is used as  the  underlying
  type  for  an enumeration except that the underlying type shall not be
  larger than int unless the value of an enumerator cannot fit in an int
  or unsigned int.  If the enumerator-list is empty, the underlying type
  is as if the enumeration had a single enumerator with  value  0.   The
  value of sizeof() applied to an enumeration type, an object of enumer-
  ation type, or an enumerator, is the value of sizeof() applied to  the
  underlying type.

This does not make the code _not_ C++.  My contention remains, calling 
the code not C++ is wrong and misleading.