How can I simulate OO-style polymorphism in C?

Question

Is there a way to write OO-like code in the C programming language?

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See also:

• Can you write object-oriented code in C?
• Object-orientation in C

Found by searching on "[c] oo".

Answer 1

The first C++ compiler ("C with classes") would actually generate C code, so that's definitely doable.

Basically, your base class is a struct; derived structs must include the base struct at the first position, so that a pointer to the "derived" struct will also be a valid pointer to the base struct.

typedef struct {
   data member_x;
} base;

typedef struct {
   struct base;
   data member_y;
} derived;

void function_on_base(struct base * a); // here I can pass both pointers to derived and to base

void function_on_derived(struct derived * b); // here I must pass a pointer to the derived class

The functions can be part of the structure as function pointers, so that a syntax like p->call(p) becomes possible, but you still have to explicitly pass a pointer to the struct to the function itself.