C++ string class

If you have a C++ string and a char pointer

string str = "mudkipz";
char * ptr;

how would you iterate through each char in the string using only the pointer and only pointer notation? In other words, you can't assign the address with ptr = &str[0];

I don't see how it's possible, since a string isn't an array. If it were, I'd just do this

string str = "mudkipz";
    char * ptr = str;

    for(int i = 0; i < str.length(); ++i)
    {
        cout << *(ptr + i);
    }

Any ideas?

>>4
One of the many things that we tend to talk about here are the design of programming languages and their consequences. If you are not interested in this, and only want help with your homework, I suggest that you kindly take your questions to your professor or teaching assistant. Thank You