?

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 0;
}

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

??? s.erase(0,s.find_first_not_of(" "));
??? s.erase(s.find_last_not_of(" ") + 1);
??? return s;
}