Time spent on design, implementation, and tests: 5.5 hours.

The placement of the definitions inside the header files is intentional, so to aid the browsing among files.

1. Current employees are read out from a file.

2. Settings are read out from a file (as was specified) at the time of creation of first instance of some class derived from the Account class. Afterwards, settings are stored as a static std::unordered_map, which maps a wage category name (std::string) to a wage (double). While it is a common knowledge to not store money values in floating point types, yet this good practice was omitted for simplicity here. Also, the use of std::string as a label for a wage category may need a reconsideration.

3. Both Staff.h and Settings.h read from text files, so both inherit from a DataFile class which factors out common file management issues.

4. File names are hardcoded as preprocessor macros.

5. The implementation of the Singleton is thread safe due to the fact that "such a variable is initialized the first time control passes through its declaration; such a variable is considered initialized upon the completion of its initialization" - and then - "if control enters the declaration concurrently while the variable is being initialized, the concurrent execution shall wait for completion of the initialization".