ObjectARX defines a few data types for compatibility with the AutoCAD environment. It also defines a number of symbolic codes for values passed by functions (or simply for general clarity). Finally, it declares and initializes a few global variables. The definitions and declarations appear in the ObjectARX header files.
If an application does not adhere to the conventions imposed by the definitions and declarations described in this section, it will be difficult to read and maintain at best; at worst, it will not communicate with AutoCAD correctly. Also, future versions of ObjectARX may involve changes to the header files. Therefore, do not substitute an integer constant for its symbolic code if such a code has been defined.