std::move()

 #include <iostream>
 #include <utility>
 #include <vector>
 #include <string>
 int main()
 {
     std::string str = "Hello";
     std::vector<std::string> v;

     // uses the push_back(const T&) overload, which means
     // we'll incur the cost of copying str
     v.push_back(str);
     std::cout << "After copy, str is \"" << str << "\"\n";

     // uses the rvalue reference push_back(T&&) overload,
     // which means no strings will copied; instead, the contents
     // of str will be moved into the vector.  This is less
     // expensive, but also means str might now be empty.
     v.push_back(std::move(str));
     std::cout << "After move, str is \"" << str << "\"\n";

     std::cout << "The contents of the vector are \"" << v[]
                                          << "\", \"" << v[] << "\"\n";
 }

最好配合着c++标准库一起看。