A memory mapped file can be used to store complex object oriented structures if you make use of 'relative' pointers, where you have to add the address of the pointer to the pointer to get to the object you are pointing to. I once used this method, to persist a complex data structure without having to write serialization code.

A long time ago, I implemented some C++ classes that would hide most of the additional work and also took care of allocating new objects inside the memory mapped file. See: https://www.iwriteiam.nl/D0205.html#13MMF (Note that this implementation actually makes use of a slightly different approach where pointers are relative with respect to the first position of the file. This implementation has the limitation that you can only open one such store as a memory mapped file. It was only later I realized that it was possible to do without the offset. I never came to rewriting all the code.)