I have a std::map<int, Point> keyed by the points id. I need to do the equivalent of a memcpy into a pointer like the following.

struct Point {
    float x, y, z;
    float nx, ny, nz;
};

// ...

std::map<int, Point> meshA = submesh.at(2);

Point* points = reinterpret_cast<Point*>(OGRE_MALLOC_SIMD(sizeof(Point) * totalPoints(), Ogre::MEMCATEGORY_GEOMETRY));

// memcpy into points?
  

After allocating the memory, how does one do the equivalent of a memcpy of std::map<int, Point> into 'Point* points'? I have to populate this pointer (Point *) which is the type my engine API takes.

Do you just want the 'Point' instances from the map, without the IDs? [Edit: I'm guessing that's the case based on the use of 'Point *', but it might still be worth clarifying that.] And does order matter? (E.g. do you want the points ordered by ascending ID?)

Yeah, I should have clarified that.

No, the point id's wouldn't be a part of it. Just the point structures. Yes, order does matter.

Assuming the order you want is by ascending ID, then I think you'll need to iterate over the map and process each 'Point' instance one at a time (either implicitly or explicitly - there are various ways you could express it using standard library features).

There may be other issues involved, such as padding, alignment, reinterpret_cast vs static_cast, and so on, but I don't know much about the context you're working in, so I won't comment on those issues. It sounds like the key question though is how to extract the 'Point' instances from the map, and I think the answer is that, one way or another, it needs to be done one at a time.

You could way more simple store all your points in memory and have the map just point to an Integer to Point-Pointer pair instead of to just the Point instance itself