Re: How would you update this array? Help with logic.

From:

Dan Bloomquist <public21@lakeweb.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Sun, 09 Mar 2008 21:06:49 GMT

Message-ID:

<JjYAj.5819$7d1.1053@news01.roc.ny>

Simon wrote:

This is still unclear. Suppose I get items

{1, 2, 3}

then to update them, I see

{1, 2, 3}

but I might get a new point

{1, 2, 3, 4}

and then lose a point

{2, 3, 4}

Note that at all times, there is exactly enough information to
re-create the entire set of
std::map elements. Therfore, there is no need to worry about how to
"delete something
that isn't in the map" because if it is not in the update set, it is
not in the map, and
therefore you can re-create the entire map "from scratch" at any time.

No, suppose I have a map

std::map< int, myClass*> myMap;

And I add 2 items ( myMap.insert( std::pair<...>) );

I now have 2 items in the map.

Then I call the update function to update both items with some data for
myClass*

That wasn't really clear as you started your example with an assignment.
But yes, you said then you would want to come along and update the data.

So add to your update method:

    std::set< int > setInUse;

    //Update loop i
    {
       ...
       setInUse.insert( i );
    }

    for( MyMapIt it= maMap.begin( ); it != myMap.end( ); )
       if( setInUse.find( it->first ) == setInUse.end( ) )
          it= myMap.erase( it );
       else
          ++it;

Best, Dan.