C and C++: a Case for Compatibility

This article presents a case for significantly increasing the degree of compatibility between C and C++. The ideal proposed is full compatibility. This ideal is not trivially obvious nor technically easy to achieve. Therefore, arguments against full compatibility are presented as well as arguments for. A companion paper [Stroustrup,2002a] provides a ‘‘philosophical’’ view of the C/C++ relationship, and a follow-up article will present some examples of how incompatibilities might be resolved [Stroustrup,2002c]. 1 Languages and Communities Modern C [C89] [C99] and C++ [C++98] are sibling languages [Stroustrup,2002] [Stroustrup,2002a] descended from Classic C [Kernighan,1978]. In many people’s minds they are (wrongly, but understandably) fused into the mythical C/C++ programming language. There is no C/C++ language, but there is a C/C++ community. The primary aim of this article is to examine how the future evolution of C and C++ can best serve that community. My claim is that a significant increase in the degree of C/C++ compatibility best serves the interests of the C/C++ community and that the ideal is full C/C++ compatibility. What is the C/C++ community? Millions of programmers use C and/or C++ so any individual and any organization necessarily has an incomplete picture of the situation and often a biased one. Consider for a moment three groups: [1] programmers who use C only [2] programmers who use C++ only [3] programmers who use both C and C++ Within each group, we can again look at a multitude of classifications. For example, students, teachers, occasional programmers, games programmers, builders of large systems, embedded systems programmers, scientific/numeric programmers, builders of small commercial applications, programmers with a great need for portability, builders of applications embedded in large commercial frameworks, software tool builders, programmers of large infrastructure applications, etc. It is hard to place an individual in a single category. Importantly, many programmers belong to several of these groups and subgroups during a career, even if they are currently comfortable in some single category. Are there people who use C++ and never C? Of course there are many C++ programmers who never compiled a C source file, but how many C++ programs don’t call a C library? If a C library is used directly, the programmer must understand the constructs appearing in its header files. Even if C code is used only indirectly, some aspects of C must often be taken into account, such as C’s use of m a l l o c () rather than n e w , the use of arrays rather than C++ standard library containers, and the absence of exception handling. The use a C in one part of a program often affects other parts of the program, so that a C++ programmer must be aware of C. And of course, the C++ standard library includes the C89 standard library. It is only a slight exaggeration to say that all C++ programmers are C programmers. On the other hand, there are C programmers who never use C++. This is obviously true for programmers who – especially in the embedded systems community – work on a platform for which no C++ compiler exist. There are fewer such platforms than there used to be, though, and not all of those support ISO Part of a three-article series from "The C/C++ Users Journal" July, August, and September 2002