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Re: pointer member constant expression
On Feb 24, 2006, at 8:55 AM, Richard Guenther wrote:
On 2/24/06, Perry Smith <pedz@easesoftware.net> wrote:
I have asked this question before -- maybe to the gcc-help list but
I'm still unclear.
The problem is this:
struct foo {
int a;
int b;
int c;
};
static const int foo::*j = &foo::c; // accepted
class dog {
static const int foo::*k = &foo::c; // error
};
5.19 (constant expressions) paragraph 2, the last item in the 1998 C+
+ spec says " -- a pointer to member constant expression." That
appears to be defined as: '&' qualified-id (5.19 paragraph 6).
So is the line in error legal C++ or not?
No.
t.C:10: error: 'foo::c' cannot appear in a constant-expression
t.C:10: error: `&' cannot appear in a constant-expression
t.C:10: error: invalid in-class initialization of static data member
of non-integral type 'const int foo::*'
But '&' can occur in a constant-expression and 'foo::c' is a unique-id
which can also appear in a constant expression (see 5.19). And as
far as the static const data member, 9.4.2 paragraph 4 says:
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
(5.19). In that case, the member can appear in integral constant
expressions within its scope. The member shall still be defined in
a namespace scope if it is used in the program and the namespace
scope definition shall not con- tain an initializer.
Note that 5.19 states that '&foo::c' is an integral constant
expression. So I draw the conclusion that k is a const integral
type (but I have not seen a place in the spec that actually says
that a pointer to member is an integral expression but what else
could it be?
Sorry to be a pest but I just don't see why my construct is excluded.
Thank you for your time and patience,
Perry