find nth word in sentence c++

#include <iostream>
#include <string>
#include <vector>

using namespace std;

void splitString(const string &str, vector<string> &output)
{
    string::size_type start = 0; // Where to start
    string::size_type last = str.find_first_of(" "); // Finds the first space

    // npos means that the find_first_of wasn't able to find what it was looking for
    // in this case it means it couldn't find another space so we are at the end of the
    // words in the string.
    while (last != string::npos)
    {
        // If last is greater then start we have a word ready
        if (last > start)
        {
            output.push_back(str.substr(start, last - start)); // Puts the word into a vector look into how the method substr() works
        }

        start = ++last; // Reset start to the first character of the next word
        last = str.find_first_of(" ", last); // This means find the first space and we start searching at the first character of the next word
    }

    // This will pickup the last word in the file since it won't be added to the vector inside our loop
    output.push_back(str.substr(start));
}

int main()
{
    string myString("how are you doing");
    vector<string> words;
    splitString(myString, words);

    for (auto i = 0; i != words.size(); ++i)
        cout << words[i] << endl;
}