It's funny that people object to C++ while having no problem with GObject model which is a bit like doing the work of Cfront manually. The worst of both worlds and I am saying this as someone who generally prefers C to C++.

As someone on the C++ side of the fence I once did something similar.

Our data structures second term required a medium size project in C for a DB management system based on B-Tree and low level i-node manipulation.

I decided to go with anonymous structs, using pointer fields as methods, so something like GObject. Additionally each translation unit played the role of a poor man's module.

While it was an interesting experience, it isn't something I ever considered doing again.