[ub] type punning through congruent base class?

Jason Merrill jason at redhat.com
Mon Jan 6 19:22:24 CET 2014


On 01/06/2014 04:26 AM, Fabio Fracassi wrote:
> if it is not (legal): could we make it legal or would we run afoul of
> the aliasing rules?

The access is not allowed by the aliasing rules in 3.10.  But it seems 
that this would be:

struct B {
   int i;
};

struct D {
   B bmem;
   void foo() { /* access bmem.i */ }
};

B b;
reinterpret_cast<D&>(b).foo();

because B is a non-static data member of D, and 9.2/19 guarantees that 
the address of D::bmem is the same as the address of the D object.

Jason



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