std::unordered_map<Key,T,Hash,KeyEqual,Allocator>::end, std::unordered_map<Key,T,Hash,KeyEqual,Allocator>::cend

#include <cmath>
#include <iostream>
#include <unordered_map>
 
struct Node { double x, y; };
 
int main()
{
 Node nodes[3] = {{1, 0}, {2, 0}, {3, 0}};
 
 // mag is a map mapping the address of a Node to its magnitude in the plane
 std::unordered_map <Node*, double> mag =
 {
 { nodes + 0, 1 },
 { nodes + 1, 2 },
 { nodes + 2, 3 }
 };
 
 // Change each y-coordinate from 0 to the magnitude
 for (auto iter = mag.begin(); iter != mag.end(); ++iter)
 {
 auto cur = iter->first; // pointer to Node
 cur->y = mag[cur]; // could also have used cur->y = iter->second;
 }
 
 // Update and print the magnitude of each node
 for (auto iter = mag.begin(); iter != mag.end(); ++iter)
 {
 auto cur = iter->first;
 mag[cur] = std::hypot (cur->x, cur->y);
 std::cout << "The magnitude of (" << cur->x << ", " << cur->y << ") is ";
 std::cout << iter->second << '\n';
 }
 
 // Repeat the above with the range-based for loop
 for (auto i : mag)
 {
 auto cur = i.first;
 cur->y = i.second;
 mag[cur] = std::hypot (cur->x, cur->y);
 std::cout << "The magnitude of (" << cur->x << ", " << cur->y << ") is ";
 std::cout << mag[cur] << '\n';
 // Note that in contrast to std::cout << iter->second << '\n'; above, 
 // std::cout << i.second << '\n'; will NOT print the updated magnitude
 }
}

The magnitude of (3, 3) is 4.24264
The magnitude of (1, 1) is 1.41421
The magnitude of (2, 2) is 2.82843
The magnitude of (3, 4.24264) is 5.19615
The magnitude of (1, 1.41421) is 1.73205
The magnitude of (2, 2.82843) is 3.4641