C_inherritance

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

struct Base_;

typedef struct Base_VTable_
{
    char* (*ToString)(struct Base_*);
} Base_VTable;

Base_VTable Base_VTable_Obj;

typedef struct Base_ 
{
    Base_VTable* vtable;
} Base;

void Base_Init(Base* this)
{
    this->vtable = &Base_VTable_Obj;
}

typedef struct Derived_
{
    Base base;

    int a;
} Derived;

char* Derived_ToString(Derived* this)
{
    char buffer[80];

    sprintf(buffer, "%d", this->a);

    return strdup(buffer);
};

void Derived_Init(Derived* this)
{
    Base_Init((Base*)this);

    this->a = 42;

    ((Base*)this)->vtable->ToString = Derived_ToString;
}

int main()
{
    Derived d;

    Derived_Init(&d);

    char* str = ((Base*)&d)->vtable->ToString(&d);

    puts(str);

    free(str);
}