Possible Duplicate:
non-copyable objects and value initialization: g++ vs msvc
Value-initializing an automatic object?
Consider the following statement:
It's not really possible to value-initialize an automatic object.
Is this statement true? I see no problem in doing this:
int main()
{
int i = int();
}
The term value-initialization is defined in 8.5 [dcl.init] paragraph 16, 4th bullet:
If the initializer is (), the object is value-initialized.
That is, value-initialization of an automatic variable would look like this:
int i();
However, this is a declaration of a function called i returning an int. Thus, it is impossible to value-initialize an automatic. In your example, the temporary is value-initialized and the automatic variable is copy-initialized. You can verify that this indeed requires the copy constructor to be accessible using a test class which doesn't have an accessible copy constructor:
class noncopyable {
noncopyable(noncopyable const&);
public:
noncopyable();
};
int main() {
noncopyable i = noncopyable(); // ERROR: not copyable
}