This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: g++4.0 diagnostic on casting a static const member initializer to a double
- From: Matt Austern <austern at apple dot com>
- To: Mark Mitchell <mark at codesourcery dot com>
- Cc: gcc at gcc dot gnu dot org, Fariborz Jahanian <fjahanian at apple dot com>
- Date: Mon, 31 Jan 2005 10:21:20 -0800
- Subject: Re: g++4.0 diagnostic on casting a static const member initializer to a double
- References: <539EBBFC-73AE-11D9-8C44-000393B9ED88@apple.com> <41FE75E3.8080602@codesourcery.com>
On Jan 31, 2005, at 10:16 AM, Mark Mitchell wrote:
Fariborz Jahanian wrote:
g++ 4.0 in FSF issues a diagnostic on the following test case:
template <class T> struct S {
static const double scd = (double)24;
};
test1.C:2: error: a cast to a type other than an integral or
enumeration type cannot appear in a constant-expression
Rewriting the above to:
template <class T> struct S {
static const double scd;
};
template <class T>
const double S<T>::scd = (double)24;
Compiles. Event though the diagnostic is clear in what it is saying,
but it seems to be a g++ bug
one way or the other.
No, the input program is invalid. From [class.static.data]:
"If a static data member is of const integral or const
enumeration type, its declaration in the class definition can specify
a constant-initializer which shall be an integral constant
expression(_expr.const_)."
The diagnostic could be better, but it is indeed accurate; if there's
an initializer it must be integral constant-expression, and a cast to
"double" cannot appear in such an expression.
Hm, I think it's stretching it a bit to call that diagnostic accurate.
The real user error is trying to initialize a static const double in
the first place, not the details of what we're trying to initialize it
with.
You're right that this code is invalid, but I think your average user
who gets this error message might be mystified about what's wrong.
--Matt