C++ includes a number of features that don’t exist in C with an FFI impact:

Overloading: Overloads become impossible to express because of name mangling

Exceptions: Must catch exceptions at the FFI boundary and convert them to error codes, as escaping exceptions in extern "C" functions constitute undefined behavior

Destructors: C callers won’t run destructors; must expose explicit *_destroy() functions

Non-POD types: Must use opaque pointers across the FFI boundary as pass by value does not make sense

Templates: Cannot expose directly; must instantiate explicitly and wrap each specialization