Vector Testing - A gist about using myNewVector.at(int) syntax over myNewVector[int] syntax to ensure range checking is performed

vector_testing.cpp

#include <vector>
#include <iostream>

int main(){
    //Create a C++ vector
    std::cout << "Creating a new vector v" << std::endl;
    std::vector<int> v;
    //Add the int 1 to the first position (position 0)
    std::cout << "Adding 1 to position 0" << std::endl;
    v.push_back(1);
    //Add the int 2 to the second position (position 1)
    std::cout << "Adding 2 to position 1" << std::endl;
    v.push_back(2);
    //Add the int 3 to the third position (position 2)
    std::cout << "Adding 3 to position 2" << std::endl;
    v.push_back(3);
    //Loop through the vector to see the 3 int values in their correct positions
    std::cout << std::endl << "Let's iterate through the vector" << std::endl;
    for (int i = 0; i < v.size(); i++)
    {
    	std::cout <<  "Number " << i << ":" << v[i] << std::endl;
    }
    //Remove the int at the very end of the vector
    std::cout << std::endl << "Let's remove the integer 3 which is sitting in position 2 of the vector ..." << std::endl;
    std::cout << "v.pop_back();" << std::endl;
    v.pop_back();
    std::cout << "Done!" << std::endl;
    //Loop through the vector to see that the value (which we removed) is not being displayed
    std::cout << std::endl << "Let's again iterate through the vector, notice that there is one less integer being listed this time" << std::endl;
    for (int i = 0; i < v.size(); i++)
    {
    	std::cout <<  "Number " << i << ":" << v[i] << std::endl;
    }
    //Interestingly, if we use the v[int] syntax to access the vector, we can see that the int 3 is still in position 2 of the vector. 
    //Even though we removed it using v.pop_back() above.
    std::cout << std::endl << "Interestingly, the missing element still exists when using the v[int] syntax to query the vector" << std::endl;
    std::cout << "v[2]" << std::endl;
    std::cout << std::endl << v[2] << std::endl;
    //A safer way to access the vector is by using the v.at(int) syntax. This method has built in range checking.
    std::cout << std::endl << "A safer way to access the vector is by using the v.at(int) syntax";
    std::cout << std::endl << "For example, the element does not exists using v.at(1) ...";
    std::cout << "This following command should fail to retrieve the int 3 in position 2 and is evidenced by the following error message ..." << std::endl;
    std::cout << "v.at(2) ... Here goes ..." << std::endl << std::endl;
    std::cout << v.at(2) << std::endl;
    return 0;
}

/*


The above code produces the following output

Creating a new vector v
Adding 1 to position 0
Adding 2 to position 1
Adding 3 to position 2

Let's iterate through the vector
Number 0:1
Number 1:2
Number 2:3

Let's remove the integer 3 which is sitting in position 2 of the vector ...
v.pop_back();
Done!

Let's again iterate through the vector, notice that there is one less integer being listed this time
Number 0:1
Number 1:2

Interestingly, the missing element still exists when using the v[int] syntax to query the vector
v[2]

3

A safer way to access the vector is by using the v.at(int) syntax
For example, the element does not exists using v.at(1) ...This following command should fail to retrieve the int 3 in position 2 and is evidenced by the following error message ...
v.at(2) ... Here goes ...

terminate called after throwing an instance of 'std::out_of_range'
  what():  vector::_M_range_check: __n (which is 2) >= this->size() (which is 2)
Aborted (core dumped)


*/

Using the myNewVector[int] syntax to retrieve values from a C++ vector can produce undefined behavior.
It is my belief, but I need to investigate further, that if the std::vector is inherited into a class then the range checking syntax of myNewVector.at(int) is not available.