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

David Wilkinson <>
Sat, 07 Feb 2009 10:20:27 -0500
Simon wrote:


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

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?


Maybe I'm missing something but don't these rules just mean that your original
container should be set equal to the new one?

_data = newdata;

David Wilkinson
Visual C++ MVP

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