Re: [Boost-users] metaprogramming help

At Tue, 14 Dec 2010 10:44:12 +0100, Sebastian Redl wrote:

On 14.12.2010 01:29, Dave Abrahams wrote:

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At Mon, 13 Dec 2010 18:52:34 -0500, John Dlugosz wrote:

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[1] [1.1] A couple of times I've run into the situation where a "new" C++ class is written to exactly match "legacy" C structures. At the edges where old code meets new code, you can cast one to the other in-place. For example, given a huge mess of data that includes oldstruct s1; you could write the line newclass& s2= reinterpret_cast(s1); because s2 is designed to exactly overlay s1. 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)); 5.2.10p7 in the current draft defines the semantics of reinterpret_cast between standard-layout types via this double static_cast, so there is no difference.

That's an draft for C++0x. I assume the OP wants the code to work under C++03. -- Dave Abrahams BoostPro Computing http://www.boostpro.com