Help with some logic, best way to update a container.

From:
"Simon" <spambucket@example.com>
Newsgroups:
microsoft.public.vc.mfc
Date:
Sat, 7 Feb 2009 14:06:26 +0200
Message-ID:
<6v5bqnFi9u6bU1@mid.individual.net>
Hi,

In my application I have a container, (a list, map, vector, an array, ...
whatever), and I want to update some of the values.
I was wondering what would be the most efficient way of updating such a
list.

For example Assuming I have a vector, (excuse the pseudo code).

std::map<int, int> _data;
_data.[ 0] = 0; // #0
_data.[ 1] =1; // #1
_data.[ 2] =2; // #2
_data.[ 3] =3; // #3

further down the app I want to 'update' those values.

void Update( const std::map<int, int>& newData )
{
 ...
}

where "newData" is another container that contains the new values.
what I want to do is
1) If the value already exists in my container, update it
2) If the value does not exits in the container add it.
3) If the value is not present in the new container I need to remove it from
my container.

1 and 2 are fairly straight forward, but how would you do 3 in an efficient
way?

I could go around the current container and look in the new container for
the id, (and if it is not present remove it), but that does not strike me as
very efficient.
I cannot just copy one container over another as the 'newData' only contains
part of the data held by the actual container.

How would you update a container?

Many thanks
Regards.

Simon

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