It is often necessary to store data in the Archicad project file, which is 'owned' by you. Archicad should know nothing about this data (except the fact which add-on created/stored it). It just saves the specified number of bytes in the appropriate places and provides the possibility to make operations on them.

There are six ways to save custom data in an Archicad project:

You can save any number of bytes in the Archicad Preferences file,
You can save your own sections in any library part,
You can assign data to any Archicad floor plan element or attribute,
You can create Groups with arbitrary amount of data assigned to them,
Your add-on can save its data in an Archicad project file as module data,
You can also form element sets out of a group of elements, and attach custom data to it.

Important note

All of this data is saved into the project and archive files. These files are platform independent, so you must watch out for byte ordering in case of binary data. Archicad cannot do the necessary byte swapping procedure for you, because it doesn't know anything about the structure of your data. If you intend to compile your add-on both on the Macintosh and the Windows platform, you must address this issue.