Implement a statistics HTTP server

So this seems problematic.  :-(

This is a definition of... a global variable I think?

First, you can't have definitions in .h files - because every .cpp file that includes the .h will make another copy of the variable and you'll get a fatal error when you link.

If you have a global variable, the way to do it is to _declare_ it in the .h file, and then _define_ it in one place in a .cpp file.

BUT global variables are bad. We basically disallow them entirely even for the most central purposes.

* What if you want more than one copy of this service?  They'll have to share the same global variable, which wouldn't work at all in your case, but even in the general case, would involve thread safety issues.

* When is this variable constructed?  When is it destroyed?  The answer is complex and varies between platforms and compilers.  But if there are multiple global variables that depend on each other, it is quite possible that one global variable will be able to see another after it has been destroyed.  Worse, the state of this issue might change without changing any of the code directly involved - so code that previously worked fine will stop working without any obvious reason.

* (Less important, we reserve the _ suffix for class members.)