On 11/07/2010 05:29 AM, Benoit Jacob wrote:
This code:
static const unsigned x = (unsigned)-1;
enum e {
ey = (int)x
};
relies on the constant global variable x being a true compile-time
constant, right?
But as far as I can see, it is impossible to guarantee that it
actually is, since in theory you could do
const_cast<int*>(&x) = 0;
The standard says,
Except that any class member declared mutable (7.1.1) can be modified,
any attempt to modify a const object during its lifetime (3.8) results
in undefined behavior.
So the above assignment has undefined behavior, which means the compiler
is allowed to assume that it doesn't happen.
I guess that the only way is to say that the compiler remembers the
initializer value -1 for x and uses it instead of x itself. In other
words x itself is never used.
Right.
I guess that this is where the "static"
matters here since inside of one translation unit the initializer
value -1 can be remembered?
'static' doesn't matter, just that it's const, integral, and initialized
with a constant expression.
Jason
