I am having a base class that has 5 subclasses.
If in my base class I have this:
virtual CpuPort &getsecondDataPort()=0;
then this means that the method has to be implemented for all the subclasses, right?
But I do not want that, since I know that I will call that method only when I have an object of the specific subclass so I thought that I could write this instead:
virtual CpuPort &getsecondDataPort();
and implement it only in the subclass I want. But that gives me this error:
/base.cc:254: undefined reference to `vtable for BaseCPU'
and in the from the other subclasses :
undefined reference to `typeinfo for BaseCPU'
where BaseCPU is my object of the base class.
Because it is part of a bigger library (simulator actually), I want to make as fewer changes as possible. So please do not suggest something like 'define that oonly in your subclass' as I want to follow the way code is organized so far, unless this is the only way of fixing the problem.
Any idea on why that might happen?
Thanks
this means that the method has to be implemented for all the subclasses, right?
Only if you want to create direct instances of those subclasses. If a subclass does not implement a pure virtual function, it will be abstract - which is allowed per se.
But that gives me this error:
This is because the virtual function is declared, but not defined. You have to provide a definition if the function is not pure virtual.
In this case, you can not provide a dummy implementation that does nothing, because your function is supposed to return a reference, and flowing off the end of a value-returning function without returning anything is Undefined Behavior per Paragraph 6.6.3/2 of the C++11 Standard.
If your base class has a data member of type CpuPort called (say) myCpuPort, on the other hand, you could do this:
virtual CpuPort &getsecondDataPort() { return myCpuPort; }