In C++, when you copy a struct instance to another instance, the runtime knows if any fields (to whatever depth) have manually defined assignment or move operat

In C++, when you copy a struct instance to another instance, the runtime knows if any fields (to whatever depth) have manually defined assignment or move operators and will call them in the proper order. So it's a deep copy. The same information is used for calling any field constructors and destructors that are user defined. Introspection (reflection) would go even further and provide at runtime all the information that you have at compile time about an object. But that's not required for assignment and destruction operations to work. C doesn't have any of that, so a struct copy is just a shallow copy, a bit by bit copy of the entire struct contents. Which works pretty well, except for pointers/references.