Iterator Invalidation in C++ program

In this tutorial, we will be discussing a program to understand iterator invalidation in C++.

While iterating over the elements of a container object, sometimes it can become invalidated if we don’t apply bound checks. This mainly occurs due to the change in the shape and size of the container object.

Example

#include <bits/stdc++.h>
using namespace std;
int main() {
   //declaring a vector
   vector <int> v{1, 5, 10, 15, 20};
   //changing vector during execution
   //which will cause bound invalidation
   for (auto it=v.begin();it!=v.end();it++)
      if ((*it) == 5)
         v.push_back(-1);
   for (auto it=v.begin();it!=v.end();it++)
      cout << (*it) << " ";
   return 0;
}

Output

1 5 10 15 20 -1 -1

(It may also happen that to add the new element, the vector gets copied to a new location with our iterator still pointing to the old one which will then give an error.)