stringstream and Conversions

• Using iostream, one can work with cout, cerr, and cin
  • cout and cerr are output streams
    • In addition to providing output facilities, they provide conversion support
      • Thus

        int i;
        double d;
        cout << "Hello" << i << d;
        									

        converts i and d to strings prior to sending them to the standard output
    • The same is true for an << operator overloaded for a user-defined class:

      class MyClass {
      	...
      	friend ostream &operator <<(ostream &os, const MyClass &myClass);
      	...
      }
      							

      This operator effectively converts the MyClass object, myClass to a string and sends (prints/outputs) the result to the ostream object, os.
  • cin is an input stream
    • In addition to providing input facilities, it provides conversion support
      • Thus

        int i;
        double d;
        cin >> i >> d;
        									

        converts the input (which are strings) to integer and double
• Using fstream (file stream), one adds files to the mix
  • ifstream, and ofstream
  • Input/output is now from/to a file (rather than standard input/output)
  • Conversion support is still present
• C++ also provides a set of classes whose input/output is from/to a string
  • Conversion support is still present!!!
  • istringstream - allows input from string source
  • ostringstream - allows output to string sink
  • stringstream - allows input/output from the same stream
• ostringstream
  • Use like cout
    • << operator
    • Converts operands to string for output
    • Maintains the output in the ostringstream object
      • Internal buffer
  • Result is retrieved using str() function
• istringstream
  • Constructor takes string that will be the input source
  • Use like cin
    • operator
    • Converts input to operand types
• stringstream
  • Allows for both input and output
  • good for dynamically created strings
  • build up (insert) using <<
  • extract using >>

Code for String Streams