better string split for C++

bettersplit.cpp

// O(n)
int split(vector<string> &tokens, const string &str, const string &delim)
{
    int count = 0;
    auto begin = str.begin();
    auto it = str.begin();
    auto end = str.end();
    
    while (begin != end && it != end) {
        
        while (it != end && delim.find(*it) == string::npos) {
            it++;
        }
        
        if (it - begin > 0) {
            count++;
            tokens.push_back(string(begin, it));
        }
        
        if (it != end) {
            it++;
            begin = it;
        }
    }
    
    return count;
}