去除string前面或后面的空白符

// trim from start (construct new string)
    inline std::string ltrim(const std::string &str)
    {
        std::string s(str);
        s.erase(s.begin(), std::find_if_not<decltype(s.begin()), int(int)>(s.begin(), s.end(),
                std::isspace));
        return s;
    }

    // trim from end (construct new string)
    inline std::string rtrim(const std::string &str)
    {
        std::string s(str);
        s.erase(std::find_if_not<decltype(s.rbegin()), int(int)>(s.rbegin(), s.rend(),
                std::isspace).base(), s.end());
        return s;
    }
  // trim from both ends
  inline std::string &trim(std::string &s) {
    return ltrim(rtrim(s));
  }