Modifying constant vector in C++

Question

I had a question on the Pramp platform. The task was to reverse words in a given string(a vector of chars). They expected a solution with no extra space, however the vector passed in the function was a 'const'.

vector<char> reverseWords(const vector<char>& arr ) 

So is there a way to modify a const vector? Or is there something that I don't get about const?

Answer 1

You need to use a new vector inside the function which uses the values from the const vector, and then returns that.

vector<char> reverseWords(const vector<char>& arr )
{
    vector<char> newArr;
    
    // Do stuff with arr and newArr
    ...

    return newArr;
}

Answer 2

you can shoot yourself in foot via:

auto newVec = const_cast<vector<int>*>(&vec);

that means you are breaking your promise.

The right approach here as suggested by the others would be, to make your own copy and modify your copy.