It\'s common to see a _var variable name in a class field. What does the underscore mean? Is there a reference for all these special naming conventions?
_var has no meaning and only serves the purpose of making it easier to distinguish that the variable is a private member variable.
In C++, using the _var convention is bad form, because there are rules governing the use of the underscore in front of an identifier. _var is reserved as a global identifier, while _Var (underscore + capital letter) is reserved anytime. This is why in C++, you'll see people using the var_ convention instead.