The Evolution of C++: 1985 to 1989

The Ct+ Programming Language [Stroustrup 1986] describes Cr+ as defrned and implemented in August 1985. This paper describes the growth of the language since then and clarifies a few points in the defrnition. It is emphasized that these language modifications are extensions; Cr+ has been and will remain a stable language suitable for long term software development. The main new featurei of Cr-+ are: multiple inheritance, type-safe linkage, better resolution of overloaded functions, recuriive definition of assignment and initialization, better facilities for user-defrned memory management , abstract classes, static member functions, const member functions, protected members, overloading of operator->, and pointers to members. These features are provided in the 2.0 release of Cr+. This paper is a revised and expanded version of a paper with a similar title. As promised in The C++ Programming Language, C++ has been evolving to meet the needs of its users. This evolution has been guided by the experience of users of widely varying backgrounds working in a great range of application areas. The primary aim of the extensions has been to enhance C++ as a language for data abstraction and object-oriented programming IStroustrup I 987a] in general and to enhance it as a tool for writing high-quality libraries of user-defined types in particular. By a high-quality library I mean a library that provides a concept to a user in the form of one or more classes that are convenient, safe, and efficient to use. In this context, safe means that a class provides a specific type-secure interface between the users of the library and its providers ; fficient means that use of the class does not impose large overhead in run-time or space on the user compared with hand written C code. Portability of at least some C+r implementations is a key design goal. Consequently, extensions that would add significantly to the porting time or to the demands on resources for a Cr+ compiler have been avoided. This ideal of language evolution can be contrasted with plausible alternative directions such as making programming convenient o at the expense of efficiency or structure;. for novices at the expense of generality;. in a specific application area by adding special purpose features to the language;. by adding language features to increase integration into a specific C++ environment. 192 Bjarne Stroustrup For some ideas of where these ideas of language evolution might lead C+r see Stroustrup 1987a, b; …