Existing formalisms of inheritance are not sufficient to model the complexities of the kind of multiple inheritance exemplified in C++.Any satisfactory formalism must model the complicating effects of virtual and nonvirtual base classes as well as virtual and non-virtual methods.By abstracting the implementational notion of a subobject and formalizing subobject selection, we develop a formalism to model this combination of features.Not intended as a formal semantics of C++, the resulting model should nevertheless provide an essential level of understanding for language theorists and implementors in their dealings with C++ and related languages.

A case study of the impact of the C++ programming language and object-oriented design on the maintenance phase of a software development project (referred to as CXR) is presented. The results show increased software reuse and reduced complexity of software changes in the parts of the project that use object-oriented design. CXR is a medium-sized software system that supports some of the operations of telephone-company central office equipment. The measurements presented identify some of the places where object-oriented programming played a significant role in increasing productivity and reducing complexity in the maintenance phase of the CXR project. The productivity of the CXR programmers was increased because they were able to reuse a large amount of existing code. The complexity in making changes to CXR's object-oriented parts was lower; for example, new features were added to CXR with fewer changes to existing function interfaces.>