C++: Reverse a string using recursion

Question

I'm trying to modify a string passing it by reference by reversing it ex: word dolphin to that it is nihplod using recurssion only. I can't add any more parameters to the function of modify its header. My output right now is od instead of dolphin , I think its only doing the last two letters, I honestly don't know why. Any thing that I should change? Here's my code.

void reverse(string &word) {
    if (word.length() == 1 || word.length() == 0) {
        if (word.length() == 1) {
            word = word;
        }
        else if (word.length() == 0) {
            word = "nothing to reverse";
        }
    }
    else {
        string temp;
        if (temp.length() == 0) {
            temp = "";
            temp = temp+word.substr(word.length() - 1, 1);
            word.pop_back();
            if (word.length() == 0) {
                word = temp;
            }
            else if (word.length() == 1) {
                //temp = temp + word.substr(word.length() - 1, 1);
                temp = temp + word;
                word.pop_back();
                word = temp;
            }
            else {
                reverse(word);
            }
        }
        else {
            temp = temp + word.substr(word.length() - 1, 1);
            word.pop_back();
            if (word.length() == 0) {
                word = temp;
            }
            else if (word.length() == 1) {
                //temp = temp + word.substr(word.length() - 1, 1);
                temp = temp + word;
                word.pop_back();
                word = temp;
            }
            else {
                reverse(temp);
            }

        }
    }


}

Answer 1

Algorithm is this:

• If the string length is less than 2, just return
• strip off the first and last chars of the word to create a substring
• recursively call reverse on your substring
• After returning from the recursion, prefix the original "last char" and postfix the original "first char" to finish the string

Here you go:

void reverse(string& word)
{
    size_t len = word.size();

    if (len < 2)
    {
        return;
    }

    char first = word[0];
    char last = word[len - 1];
    string inner;

    if (len > 2)
    {
        inner = word.substr(1, len - 2);
        reverse(inner);
    }
    word = last + inner + first;
}

Answer 2

A non-recursive way of achieving the same thing could be:

void reverseString(std::string& input)
{
    const size_t inputStringLength = input.size();
    for (size_t index = 0; index < inputStringLength/2; ++index)
    {
        // swap the character at "index" position with the character at "inputStringLength - index - 1" position
        input[index] ^= input[inputStringLength - index - 1] ^= input[index] ^= input[inputStringLength - index - 1];
    }
}

Answer 3

void rev_recv(std::string& s, int from, int to) {
    if (from >= to) return;
    rev_recv(s, from + 1, to - 1);
    std::swap(s[from], s[to]);
}

Answer 4

void reverse(string &word) 
{
    string temp = word;
    if(temp.length != 0)
    {
       cout << temp.at(temp.length()-1);
       reverse(temp.erase(temp.length()-1));
    }
    else
       cout << "\ndone\n";
}

This will print in reverse and not modify the original string that was passed in. If you want the original string modified, just remove the temp variable.