If you ignore the protection mechanisms and the class heirarchy built into C++, then a C++ class is like a C struct that can contain function pointers. For many programs this is all that's needed, and the amount of overhead involved in using such an approach to creating objects is obviously lower. So there's no question C will always be faster. It's only when you need protection and class heirarchies that C++ benefit…
> It's only when you need protection and class heirarchies that C++ benefits you. Well, need is a strong word. You might not need better correctness while still coming out way ahead by using C++.
Protection implies a much more complex structure to represent an object and class heirarchies and inheritance imply the need for a runtime. Both these overheads come at a cost. It's the nature of the program you are wriitng that determines whether you will come out ahead. If you were writing a codec, say, you would not use C++.