How to port the library to other languages?

Question

C++ / C#

The question is not about exporting functions to a library, but rather about the classes used. I know how to export code in pure C, but I don’t know how to deal with plus. For example, the same std::string lines are unlikely to be cast in the same C#, for example, to System.String lines. It is convenient to cast base types, but I don’t know what to do with classes. And I don’t know how to export my classes either.

Answer 1

For example, the same std::string lines are unlikely to be cast in the same C#, for example, to System.String lines
If only Windows, then there is COM / OLE / Active-X for this, and if for UNIX, then no classes need to be exported, only functions, the goals are not clear at all, on which OS, for which languages, it seems that you have and there is no real task, only abstract fantasies about "an ideal library in a vacuum".

Answer 2

The first option is to write a C interface for working with the library. Will work with many languages.
If you need to use C++ from a particular language, then you can use special tools. For example, to connect pluses and python, there is boost python. It allows you to do a lot of cool stuff, like working with C++ objects from python.