This pattern is licensed under the CC0 Public Domain Dedication.

Intent

Write your class type objects to an output stream.

Description

We implement operator<< on lines 13–17, which takes a reference to an std::ostream (the base class for all output streams) and the foo object we wish to write to the stream. On line 16, we simply write a string representing the foo object to the steam and return a reference to the stream itself, allowing this call to be chained.

Note that we declare this operator<< as a friend of foo on lines 6–7. This gives it access to foo’s private member, x.