Appendix C. The C++ Preprocessor

The C/C++ preprocessor is an interesting part of C's history and has been kept in C++ as it developed from C. The preprocessor is not always considered a good thing in C++, and in fact Java, which aimed to correct many of C++'s “mistakes,” left out the preprocessor. C programmers do some old-fashioned things with this facility that are considered bad manners in C++, but the preprocessor quietly performs essential things and can occasionally be very useful. In this appendix I will show the full power of the preprocessor, and why some uses are considered bad practice.