How can I provide input for my class Fred?, C++ FAQ

C++ FAQ / Section 15 / FAQ 15.10

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!

[15.10] How can I provide input for my class Fred?

Use operator overloading to provide a friend right-shift operator, operator>>. This is similar to the output operator, except the parameter doesn't have a const: "Fred&" rather than "Fred const&".

#include <iostream>

class Fred {
public:
  friend std::istream& operator>> (std::istream& i, Fred& fred);
  ...
private:
  int i_;    // Just for illustration
};

std::istream& operator>> (std::istream& i, Fred& fred)
{
  return i >> fred.i_;
}

int main()
{
  Fred f;
  std::cout << "Enter a Fred object: ";
  std::cin >> f;
  ...
}

Note that operator>> returns the stream. This is so the input operations can be cascaded and/or used in a while loop or if statement.