c++ String去除头尾空格

1.使用string的find_first_not_of,和find_last_not_of方法

 #include <iostream>
 #include <string>

 std::string& trim(std::string &);

 int main()
 {
     std::string s = " Hello World!! ";
     std::cout << s << " size:" << s.size() << std::endl;
     std::cout << trim(s) << " size:" << trim(s).size() << std::endl;

     return ;
 }

 std::string& trim(std::string &s)
 {
     if (s.empty())
     {
         return s;
     }

     s.erase(,s.find_first_not_of(" "));
     s.erase(s.find_last_not_of(" ") + );
     return s;
 }