Very subject to critcism and not commonly used or recomended, C++ had the rich feature of supporting multiple inheritence so there is no need to go a step back or a step aside and yet introduce interfaces [and probably rename the language C+-].
Any one who has ever succeeded in developing a concrete application using multiple inheritence can name a lot of drawbacks in using interfaces to acheive same functionality. Like in the case of c#, the need to define interface members (i.e. overriding functions)
in every class that implements the interface. For 100 such classes implementing an interface, 100 seperate implementations for each method, required. At least multiple inheritence can reduce the number of override(d/n) functions to ensure some code reuse.
If somehow interfaces are not limited to abstract definitions,......