The interviewer asked me this question and not sure if my answer to it was good enough or not. Anyone has any ideas?
The first thought that popped in my head was name mangling. In C++ but not in C, you can have two methods with the same name but different parameters. The compiler has to distinguish between the two methods and thus changes (mangles) the name internally.
Another thing that the C++ compiler must do that in not in C, is deal with the class inheritance. You have abstract classes, overridden methods and virtual methods. That takes a little more processing to sort out.