On Aug 1, 2012, at 11:37 PM, Larry Evans <cppljevans@suddenlink.net> wrote:
On 08/01/12 20:18, Daniel Larimer wrote:
Julien, An extra 'byte' was just left over from me testing. It works with 8 bytes (2 ints) and it asserts on 7 bytes. I was trying to find a way to 'warn' if you reserved too much. It looks like BOOST_STATIC_WARN() has been removed.
I thought about alignment issues (I am no expert here), but my understanding is that structs/classes are always 'aligned' in the same manner regardless of what is stored. Therefore, if my fwd<> class only has one data member (an array) it should be aligned appropriately for any type.
I'm pretty sure that you're array, char fwd<T,S>::_store[S], has an alignment of 1; thus, If T is double, it would not be aligned properly. You need to use an aligned buffer, which boost provides and is also in the standard someplace. boost::variant uses the boost aligned buffer for its storage buffer.
Yes, _store[S] has an alignment requirement of 1, but what is the alignment requirement for fwd<T,S>? Can we assume that this == &_store[0] ? Could we not just do 'reinterpret_cast<test*>(this)'? template<typename T, int S> struct fwd { fwd() { static_assert( sizeof(*this) >= sizeof(T) ); new (this) T(); } char _store[S]; };
HTH.
-regards, Larry
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