Using Insertion Operators and Controlling Format
This topic shows how to control format and how to create insertion operators for your own classes. The insertion (<< ) operator, which is preprogrammed for all standard C++ data types, sends bytes to an output stream object. Insertion operators work with predefined "manipulators," which are elements that change the default format of integer arguments.
https://learn.microsoft.com/en-us/cpp/standard-library/using-insertion-operators-and-controlling-format?view=msvc-170
