1. He inherited a diamond?
Two subclasses inherit the same parent class and subclass and there are two sub-classes inherit, they say the figure above shows.
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Problems, will produce ambiguity problem that calls for baseClass scope to explain the situation:
D *pd=new D;
pd->B::a=1;
pd->C::a=2;
printf("%d\n",pd->B::a);
printf("%d\n",pd->C::a);
There are two equivalent baseClass, this may not be the result we want, more difficult to call, but also a waste of memory resources in the class.
This structure is shown:
see point A of the position of the virtual function table is not the same, i.e., there are two instances baseClass!!
2. How to solve?
Use virtual inheritance!
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Memory layout:
two for baseClass is common, that is, baseClass to instantiate an object Think of what will happen to call B, C when the virtual function on a virtual table how the line, so there is a corresponding need!? virtual table corresponding points B, C, so it becomes the above structure.
! Debugging observed, it is really the case
summary: You can remove ambiguity by virtual inheritance, virtual inheritance but the cost is to increase the virtual function pointer.
