The C Preprocessor

We have already introduced the C preprocessor directives #include and #define for file inclusion and symbol definition capabilities. In this chapter, we expand the discussion to include all other capabilities of the preprocessor such as the #undef directive, the use of the conditional compilation directives #if, #ifdef, #ifndef, #else, #elif and #endif, string concatenation and token pasting. In addition, parameters for the #define directive are introduced to yield a more powerful macro facility. Some of these facilities have been defined recently in the ANSI standard and may not be available on your implementation.