C++ FAQ Celebrating Twenty-One Years of the C++ FAQ!!!
(Click here for a personal note from Marshall Cline.)
Section 15:
15.1 Advantages of <iostream> over <cstdio>?
15.2 Understanding infinite loop when the input is invalid?
15.3 How can I get std::cin to skip invalid input characters?
15.4 How does that funky while (std::cin >> foo) syntax work?
15.5 Why does my input seem to process past the end of file?
15.6 Why is my program ignoring my input request after the first iteration?
15.7 Should I end my output lines with std::endl or '\n'?
15.8 How can I provide printing for my class Fred?
15.9 Using a printOn() method vs. a friend function?
15.10 How can I provide input for my class Fred?
15.11 Providing printing for an entire hierarchy of classes?
15.12 How can I open a stream in binary mode?
15.13 "Reopening" std::cin and std::cout in binary mode?
15.14 How can I write/read objects of my class to/from a data file?
15.15 Sending objects over a network?
15.16 Backslashes in filenames?
15.17 How to capture key presses before the ENTER key?
15.18 How to turn off screen echo on keyboard input?
15.19 How can I move the cursor around on the screen?
15.20 How can I clear the screen?
15.21 How can I change the colors on the screen?
15.22 How can I print the numeric value of a char or char*? Updated!
[15.8] How can I provide printing for my class Fred?

Use operator overloading to provide a friend left-shift operator, operator<<. 

#include <iostream>

class Fred {
public:
  friend std::ostream& operator<< (std::ostream& o, Fred const& fred);
  ...
private:
  int i_;    // Just for illustration
};

std::ostream& operator<< (std::ostream& o, Fred const& fred)
{
  return o << fred.i_;
}

int main()
{
  Fred f;
  std::cout << "My Fred object: " << f << "\n";
  ...
}
We use a non-member function (a friend in this case) since the Fred object is the right-hand operand of the << operator. If the Fred object was supposed to be on the left hand side of the << (that is, myFred << std::cout rather than std::cout << myFred), we could have used a member function named operator<<.

Note that operator<< returns the stream. This is so the output operations can be cascaded.