Data encapsulation in C

Question

I am currently working on an embedded system and I have a component on a board which appears two times. I would like to have one .c and one .h file for the component.

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Answer 1

You could make a portion of your structure private like this.

object.h

struct object_public {
    uint32_t public_item1;
    uint32_t public_item2;
};

object.c

struct object {
    struct object_public public;
    uint32_t private_item1;
    uint32_t *private_ptr;
}

A pointer to an object can be cast to a pointer to object_public because object_public is the first item in struct object. So the code outside of object.c will reference the object through a pointer to object_public. While the code within object.c references the object through a pointer to object. Only the code within object.c will know about the private members.

The program should not define or allocate an instance object_public because that instance won't have the private stuff appended to it.

The technique of including a struct as the first item in another struct is really a way for implementing single inheritance in C. I don't recall ever using it like this for encapsulation. But I thought I would throw the idea out there.