#include <string>
  string substr( size_type index, size_type num = npos );

The substr() function returns a substring of the current string, starting at index, and num characters long. If num is omitted, it will default to string::npos, and the substr() function will simply return the remainder of the string starting at index.

For example:

   string s("What we have here is a failure to communicate");
   string sub = s.substr(21);
   cout << "The original string is " << s << endl;
   cout << "The substring is " << sub << endl;              

displays

   The original string is What we have here is a failure to communicate
   The substring is a failure to communicate