I need to update a Vector of pointers in C++ in a unique way

Question

So I have a vector of pointers to a class I defined. I have a function that takes the 0 index of the pointer and returns it. After that I need to remove the data in that index then take the item in the last index of the vector and put it into the 0 index. As of right now I am just setting the pointers to NULL if I return them, and then I pushback the final object in the vector and finally pop it back. I am not sure if this method is the best way of solving my issue. Here is my code though:

Instrument* loanOut() {
for (int i = 0, i < library.size(), i++) {
        if (library[i] != NULL) {
            return library[i];
        }
        else {
            return NULL;
        }
    }
    library[0] = NULL;
    library.push_back(library[library.size()]);

}

Answer 1

Algorithmically, this is what you are describing :

Object PopFrontAndReplace(std::vector<Object>& objects) {
    if (!objects.size()) {return Object();}
    Object o = objects[0];
    objects[0] = objects.back();
    objects.pop_back();
    return o;
}

Does that answer the question?