Error C2079: uses undefined class

[Igor Vartanov]

thanks for the reply. While trying to troubleshoot the problem, I stripped each class to the bare minimum functions and variables, removed all pointers and references, to hopefully figure out the cause of the problem

Your Waiter design directly requires for mandatory association between instances of waiter and table: waiter has/owns his table. While in real life he never does. There might be waiters serving no tables as well as tables currently not served at all. By removing "pointers and references" you just broke the relations you tried to model. This is not the way how problems get resolved.