On Thu, Oct 31, 2013 at 6:14 PM, MM <finjulhich@gmail.com> wrote:

On 31 October 2013 16:10, Klaim - Joël Lamotte <mjklaim@gmail.com> wrote:

What would "valid"/"invalid" means here?

If it's "exist" or "don't exist", then maybe using boost::optional<MyPod> would be enough.

That's right. How about sizeof( boost::optional<MyPod> ) vs sizeof( MyPOD ) ?

You can check it easily. On this site using Boost 1.49 I get 4 additional bytes on clang and gcc:
http://rextester.com/FMH8278

I'm a bit surprised because I thought it would be 1 byte max.

Anyway you will need a way to mark values as either valid or invalid.

There are several solutions, like using a std::vector<bool> (it's a bit vector) or boost::dynamic_bitset to have one bit

per positions telling if it's valid or not. A simpler solution would have your POD providing the info.

Also, what sort of iterator can iterate over just the valid values? or how to implement one?

Well if the container, say std::vector, already provide an iterator, you just have to wrap it by forwarding work

but just continue iterating if you just iterated into an invalid. Or better, a range. I never used boost helpers to build

ranges so I can't say more on that but you have several possibilities.

The point here is that there's a small number of elements that are invalid, their indices in the container are random,

I understand that, but I don't really see a specific problem.