C Language Preprocessor and Macros Source file inclusion
Example
The most common uses of #include preprocessing directives are as in the following:
#include <stdio.h>
#include "myheader.h"
#include replaces the statement with the contents of the file referred to. Angle brackets (<>) refer to header files installed on the system, while quotation marks ("") are for user-supplied files.
Macros themselves can expand other macros once, as this example illustrates:
#if VERSION == 1
#define INCFILE "vers1.h"
#elif VERSION == 2
#define INCFILE "vers2.h"
/* and so on */
#else
#define INCFILE "versN.h"
#endif
/* ... */
#include INCFILE
