C++ - Base class and private header

Question

I'm writing a library in C++ and have a class hierarchy like this:

message.h file (in ./mylib/src)

class Message
{
};

request.h file (in ./mylib/include/mylib)

#include "message.h"

class Request : public Message
{
};

response.h file (in ./mylib/include/mylib)

#include "message.h"

class Response : public Message
{
};

I want everything in my mylib/src folder to be hidden from user and want only to distrubute files in mylib/include. But the problem is as both requst.h and response.h #include message.h so user will get a "No such file" error when #including request.h and response.h. Is there a way to work around this problem?

Answer 1

You can simply provide a public interface for Message and keep the actual class hidden:

class IMessage
{
    Message* pImpl;
};

Distribute this header and use a forward declaration for Message.

Another option would be to use composition instead of inheritance (you'll need pointers as members, not the full object).