Converting a complex query structure to XML (for XML-RPC), how to implement?

Question

C++ / C#

Good day, I'm trying to automate some processes through the API (works on XML-RPC), while working there is a complex data structure with nestings. So far I have not figured out how to convert this structure to XML-RPC.

I would be grateful for advice, manuals, libraries. On the Internet, only examples in the form of simple structures.

PS The data structure is dynamic.