A preprocessor include directive causes the preprocessor to replace the directive with the contents of the specified file.
The preprocessor resolves macros contained in a #include directive. After macro replacement, the resulting token sequence must consist of a file name enclosed in either double quotation marks or the characters < and >. For example:
#define MONTH <july.h> #include MONTH
If the file name is enclosed in double quotation marks, (") the preprocessor searches the place (for example, directories or libraries) that contain the source files and then a standard or specified sequence of places until it finds the specified file. For example:
#include "payroll.h"
If the file name is enclosed in the characters < and >, the preprocessor searches only the standard or specified places for the specified file. For example:
#include <stdio.h>