我如何才能整体访问地图的值

Question

I have a map in c++ like this:

std::map<int, int> points;

I know that I can access the two integers for example in a for loop like this

for (auto map_cntr = points.begin(); map_cntr != points.end(); ++map_cntr)
        {
          int A = map_cntr->first; // key
          int B = map_cntr->second; // val
        }

But I want to know how I can access every point as a whole (and not it's entries like above).

I thought something like this:

for (auto map_cntr = points.begin(); map_cntr != points.end(); ++map_cntr)
            {
              auto whole_point = points.at(map_cntr);
            }

Actually, I want to do operations on integers of a entry (point) of the map with integers of the following entry (point) of the map.

Answer 1

I want to do operations on integers of a entry (point) of the map with integers of the following entry (point) of the map.

Map is not suited container to perform operation depending on the sequence of elements where you want to modify current element according to previous ones. For those things you can use a vector or an array of pairs for instance.

Answer 2

You can use foreach loop

std::map<int, int> points;

for (auto pair : points)
{
    // pair - is what you need
    pair.second;
    pair.first;
    auto whole_point = pair;

}

Answer 3

I want to do operations on integers of a entry (point) of the map with integers of the following entry (point) of the map

You can't directly modify the key of a [key,value] pair in a map. If you need to do so, you have to erase the pair and insert another one.

If you only need to write the value of a pair, or if you only need to read the pairs, you can do it with a single iterator, like this:

// assuming the map contains at least 1 element.
auto it = points.begin();

std::pair<const int, int>* currentPoint = &(*it);
it++;
for (; it != points.end(); ++it) {
    auto& nextPoint = *it;
    // Read-only: currentPoint->first, nextPoint.first
    // Read/write: currentPoint->second, nextPoint.second
    currentPoint = &nextPoint;
}

Live example