Overloading insertion operator <<

• Compiler (and library function) knows how to output standard types.

• cout << 12 << endl; // outputting an int

• cout << 12.45 << endl; // outputting a float

• cout << 'c' << endl; // outputting a char

• etc. etc.

• But, the compiler doesn't know how to output a class object.

• cout << T1 << endl; // ??????

• Defining a member function for << allows this!