Abstract classes vs Interfaces

Question

I'm a bit confused about the usage of Abstract classes in C#. In C++, it makes sense to define a template which classes inheriting the abstract class can follow. But, in C# doesn't Interface serve the same purpose?

True that abstract classes can have default implementation which is not provided by Interfaces. So if implementation doesn't need to be included in base class, is it better to go for Interfaces?

Answer 1

I still like to provide a default abstract implementation of an interface, assuming it's a substantial interface (and it makes sense). You never know when you might add something to the interface that has an easy default implementation that could be included and given "for free" to anyone who inherits from the abstract base class.

Answer 2

This CodeProject article has a lot of information on the difference between the two including a table comparing and contrasting the features of each.

Interfaces define the contract between classes - the ways classes call each other. A class can implement multiple interfaces, but can only inherit from one abstract class.