Welcome back to the 80's, where C++ used to play with macro to make templates and inheritance was only a basic compiler trick.
I can only emphasizes the need to move to real C++ if you want to use C++ idioms, to do it safely and performances wise: here you just opened the gate of Macro error's hell which will be more horrible than anything the C++ could throw at you.
The code in the article is just a plaything, a C programmer wouldn't use any of that and wouldn't use C++ as a starting point for their C implementation. Don't let it reflect negatively on C.
In what way? I have seen several examples of C programs that implemented a form of interfaces using structs of function pointers. The GIMP code base does it, as does the Linux kernel's Virtual File System layer. This is a good overview: https://www.kernel.org/doc/Documentation/filesystems/vfs.txt
Mind this is only the simplest functions and thing can already go wild if you apply classic bad C++ coding practices, like cascade inheritance or god object.
Add to that, you will (oh yes, you will, at least once) make type errors with macros, and you will fail to maintain all the class constructors and virtual functions.
I can only emphasizes the need to move to real C++ if you want to use C++ idioms, to do it safely and performances wise: here you just opened the gate of Macro error's hell which will be more horrible than anything the C++ could throw at you.