C, not C++, is the de-facto standard of UNIX and is what UNIX is written in, as well as most of it's user-based derivatives, such as Ubuntu, GNU,Fedora, and so forth.
in my opinion C++ is a somewhat rushed implementation of OOP into the existing C language. The fact that one needs to define the class interface and the concrete class itself in separate header and cpp files makes file management a unnecessary pain in the but.
Additionally, although simply using classes in C++ is workable, a completely different set of difficulties arises when trying to implement COM classes via C++. with requirements to implement IUnknown, IDispatch, IPersistFile, IObjectSafety, and goodness knows how many other COM interfaces, many of which contain basic boilerplate code (which can be easily wrapped into templates as shown by ATL).
of course this isn't really a design flaw on the part of C++ but rather the lack of anything higher-level to the C++ programmer for COM components. As an example, Visual Basic and Delphi can both implement COM classes without requiring the programmer to manually implement the various required classes (IClassFactory and so forth)