Additional Topics > External Development Guide > External Development Overview > External Definitions

# External Definitions

The file`idl_export.h`, found in the external/include subdirectory of the IDL distribution, supplies all the IDL-specific definitions required to write code for inclusion with IDL. As such, this file defines the interface between IDL and your code.

Note: If you are not writing in C, you will have to translate the definitions in this file to suit the language you are using.

Note: `idl_export.h` contains some declarations which are necessary to the compilation process, but which are still considered private to Exelis Visual Information Solutions, Inc., a subsidiary of Harris Corporation. Such declarations are likely to be changed in the future and should not be depended on. In particular, many of the structure data types discussed in this document have more fields than are discussed here—such fields should not be used. For this reason, you should always include`idl_export.h` rather than entering the type definitions from this document. This will also protect you from changes to these data structures in future releases of IDL. Anything in`idl_export.h` that is not explicitly discussed in this document should not be relied upon.

The following two lines should be included near the top of every C program file that is to become part of IDL:

#include <stdio.h>

#include "idl_export.h"