The UNIX system: Data abstraction in C

C++ is a superset of the C programming language; it is fully implemented and has been used for nontrivial projects. There are now more than one hundred C++ installations. This paper describes the facilities for data abstraction provided in C++. These include Simula-like classes providing (optional) data hiding, (optional) guaranteed initialization of data structures, (optional) implicit type conversion for user-defined types, and (optional) dynamic typing; mechanisms for overloading function names and operators; and mechanisms for user-controlled memory management. It is shown how a new data type, like complex numbers, can be implemented, and how an “object-based” graphics package can be structured. A program using these data abstraction facilities is at least as efficient as an equivalent program not using them, and the compiler is faster than older C compilers.