Guarding Header Files

The C Preprocessor

• removes whitespace
• removes comments
• processes #defines
• includes the files that are #included
• guards header files - keeps header files from being placed into a program's code multiple times.

Preprocessor Directives Used for Guarding a Header File

#ifndef _fraction_h     /* if fraction.h hasn't already been defined */
#define _fraction_h     /* then define it as the following ...       */
                        /* everything between the #define and the 
                           #endif will be considered _fraction_h  The  
<code of the               underscore which replaces the dot, is 
 header file>              necessary since the preprocessor can't
                           handle dots well.  The underscore before 
                           the filename is traditional               */

#endif