string::split c++

lv1

vector<string> split(const string& s)
{
    vector<string> ret;
    typedef string: ize_type string_size;
    string_size i = 0;

    // invariant: we have processed characters [original value of i, i) 
    while (i != s.size()) {
        // ignore leading blanks
        // invariant: characters in range [original i, current i) are all spaces
     while (i != s.size() && isspace(s[i]))
         ++i;

     // find end of next word
     string_size j = i;
     // invariant: none of the characters in range [original j, current j)is a space
     while (j != s.size() && !isspace(s[j]))
	     j++;
         // if we found some nonwhitespace characters 
         if (i != j) {
             // copy from s starting at i and taking j - i chars
             ret.push_back(s.substr(i, j - i));
             i = j;
         }
    }
    return ret;
}

lv5

template <class Out>                           // changed
void split(const string& str, Out os) {        //  changed

    typedef string::const_iterator iter;

    iter i = str.begin();
    while (i != str.end()) {
        // ignore leading blanks
        i = find_if(i, str.end(), not_space);

        // find end of next word
        iter j = find_if(i, str.end(), space);

        // copy the characters in [i, j)
        if (i != str.end())
            *os++ = string(i, j);       // changed

        i = j;
    }
}