Information Hiding with Opaque Pointers in C

Are users of your C structures reaching in and placing your structures in an invalid or inconsistent state? Are changes you make to your structures breaking your users' code? Do you need to make some of your structure members read-only, write-only, read-write, or completely invisible to your users? Using opaque pointers in C can help you a achieve a clean interface that gives you full control over the internal implementation and visibility of your structure members. We'll use Visual Studio 2019 Community edition and the C compiler built into Visual C++, but the techniques can be applied to a wide variety of C compiler implementations. (Knowledge of C structures and pointers is recommended.)