C wrapper for C++ library - what about inheritance?

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1

So I've read Developing C wrapper API for Object-Oriented C++ code and I like the approach, which I have taken with my library - opaque handles for each corresponding C++ class; avoiding using void*

But now, I'm faced with thinking about 'interfaces', and base classes. For example, I have a class hierarchy of "channel" classes - a base class for a "channel" and derived concrete classes for, for example, serial comms, in-memory buffers, sockets, etc.

So I have:

typedef struct serial_channel serial_channel;
typedef struct socket_channel socket_channel;
typedef struct memory_channel memory_channel;

serial_channel* create_serial_channel();
socket_channel* create_socket_channel();
memory_channel* create_memory_channel();

But I want to be able to pass any one of those into a function to associate it with a 'device' object:

void associate_device_with_channel(device*, channel*);

Easy in C++, since it understands base classes. How do I approach this in the C wrapper library - what type is channel in C?

The only thing I can think of is that I must resort to void* to represent a base class?

typedef void* channel;
void associate_device_with_channel(device*, channel*);

It works, but would let me pass any pointer?

On the other extreme, I can write a set of functions matching the derived channel classes:

void associate_device_with_serial_channel(device*, serial_channel*);
void associate_device_with_socket_channel(device*, socket_channel*);
void associate_device_with_memory_channel(device*, memory_channel*);

It's very verbose, and if I have to add new channel types, I have to add new functions to the interface as well.

Is there some kind of middle ground I've been missing? - like a single function, but not void*?

asked 2 mins ago

Steve Folly

2,169