Re: [Boost-users] metaprogramming help

At Tue, 14 Dec 2010 09:07:30 +0100, Roman Perepelitsa wrote:

[1 ] [1.1 ] 2010/12/14 Dave Abrahams

...

Unless oldstruct and newclass are both POD, the above has implementation-defined behavior. The portable way to do it, if they indeed have the same layout, is

newclass& s2= *static_cast(static_cast(&s1));

Using s2 causes undefined behavior (accessing an object through a pointer to unrelated type).

No, not if the types are layout-compatible. Look it up (it will cost you a thorough reading ;->).

reinterpret_cast has the same problem

reinterpret_cast causes implementation-defined, not undefined, behavior IIRC, in the cases where the static_cast approach works. -- Dave Abrahams BoostPro Computing http://www.boostpro.com