# Function Declarations

External functions are declared in include files. There are three kinds of include files:

- Application include files
- Library include files
- System include files and standard C include files

## Application Include Files

The `.c` file should `#include` its own `.h` file. A .h file should be protected so that no errors occur if it is #include'd twice. This can be done by the following directives:

    	#ifndef HTFOO_H
    	#define HTFOO_H

    	All the stuff

    	#endif /* HTFOO_H */

An interface which relies on other interfaces should include those interface files. An implementation file which uses other modules should include the .h file if it not already included by its own .h file.

The text format in description files which are converted into declaration files MUST NOT be more than 90 characters wide - otherwise it will get chopped off by the Line Mode Browser the way the conversion currently is set up.

## Library Include Files

If you are making a Library module then you need to include all the modules that you reference in your code. You will in all cases need the following:

    	#include "sysdep.h"
    	#include "WWWUtil.h"

If you are not making a Library module, then you need the following:

    	#include "sysdep.h"
    	#include "WWWLib.h"

## System include files and standard C include files

As these are included in the Library code, you will normally not need to (and should avoid) include any such files. The reason is that these include files are very difficult to get portable over multiple platforms.