F.1. Introduction

This chapter introduces the preprocessor. Preprocessing occurs before a program is compiled. Some possible actions are inclusion of other files in the file being compiled, definition of symbolic constants and macros, conditional compilation of program code and conditional execution of preprocessor directives. All preprocessor directives begin with #, and only white-space characters may appear before a preprocessor directive on a line. Preprocessor directives are not C++ statements, so they do not end in a semicolon (;). Preprocessor directives are processed fully before compilation begins.

Common Programming Error F.1

Placing a semicolon at the end of a preprocessor directive can lead to a variety of errors, depending on the type of preprocessor directive.

Software Engineering Observation F.1

Many preprocessor features (especially macros) are more appropriate for C programmers than for C++ programmers. C++ programmers should familiarize themselves with the preprocessor, because they might need to work with C legacy code.