Finding last word in a string

Question

I'm trying to return the last word in a string but am having trouble with the for loops. When I try to test the function I am only getting empty strings. Not really sure what the problem is. Any help is much appreciated.

string getLastWord(string text)

{
    string revLastWord = "";
    string lastWord = "";
    if(text == "")
    {
        return text;
    }

    for(size_t i = text.size()-1; i > -1; i--)
    {

        if((isalpha(text[i])))
        {
             revLastWord+=text[i];
        }
        if(revLastWord.size()>=1 && !isalpha(text[i-1]))
        {
             break;
        }
    }

    for(size_t k = revLastWord.size()-1; k > -1; k--)
    {
        lastWord+=revLastWord[k];
    }

    return lastWord;
}

Answer 1

I was coding up another solution until I checked back and read the comments; they are extremely helpful. Moreover, the suggestion from @JustinRandall was incredibly helpful. I find that find_last_of() and substr() better state the intent of the function--easier to write and easier to read. Thanks! Hope this helps! It helped me.

std::string get_last_word(std::string s) {
  auto index = s.find_last_of(' ');
  std::string last_word = s.substr(++index);
  return last_word;
}

/**
 * Here I have edited the above function IAW 
 * the recommendations.
 * @param s is a const reference to a std::string
 * @return the substring directly
 */
std::string get_last_word(const std::string& s) {
  auto index = s.find_last_of(' ');
  return s.substr(++index);
}

Answer 2

The other answers tell you what's wrong, though you should also know why it's wrong.

In general, you should be very careful about using unsigned value types in loop conditions. Comparing an unsigned type like std::size_t and a signed type, like your constant -1, will cause the signed to get converted into an unsigned type, so -1 becomes the largest possible std::size_t value.

If you put some print statements throughout your code, you'll notice that your loops are never actually entered, because the conditional is always false. Use an int when performing arithmetic and especially when signed numbers are compared with.