Could you describe input and output parameters in this structure.

In case of a simple structure, it's comparatively easy to assemble it in a FoxPro string. Then this structure can be passed by reference to your external function.

An example:

DECLARE INTEGER myfunction IN mylib.dll;
STRING @thestructure

Again, it depends on the structure's complexity, whether you need to use an API Structure class or just a "manual" assembling is enough.