Revisiting the preprocessor
The preprocessor is a very powerful utility; therefore, it must be used with great care. We can't eliminate it since it is an essential part of developing multi-file programs. In this section, we will explore how to use the preprocessor. Our goal is to find, just as Goldilocks did, the just-right amount of preprocessing to employ – not too much and not too little.
Introducing preprocessor directives
The preprocessor is a simple macro processor that processes the source text of a C program before the program is read by the compiler. It is controlled via single-line preprocessor directives and transforms the source text by interpreting macros embedded in the source text to substitute, add, or remove text based on the given directives. The resulting preprocessed source text must be a valid C program.
The following table provides an overview of the basic preprocessor directives:
