cmake_demo/main.c

#include <stdint.h>
#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include <assert.h>

#define VIRTUAL  
#define PRIVATE static 

#define ASSERT_CALL_VIRTUAL_METHOD() assert(!("can't call abstract method"))


struct _virtual_table
{
    VIRTUAL void (*area)(void *self);
    VIRTUAL void (*draw)(void *self);
};

void virtual_area(void *self)
{
    ASSERT_CALL_VIRTUAL_METHOD();
}

void virtual_draw(void *self)
{
    ASSERT_CALL_VIRTUAL_METHOD();
}

struct _virtual_table *virtual_new(void)
{
    struct _virtual_table *vtb = calloc(1, sizeof(struct _virtual_table));
    if (vtb == NULL)
    {
        return NULL;
    }
    vtb->area = virtual_area;
    vtb->draw = virtual_draw;
    return vtb;
}

struct _shape
{
    struct _virtual_table *vtb;
};

void shape_area(void *self)
{
    struct _shape *this = (struct _shape *)self;
    this->vtb->area(self);
}

void shape_draw(void *self)
{
    struct _shape *this = (struct _shape *)self;
    this->vtb->draw(self);
}

PRIVATE void _shape_area(void *self)
{
    ASSERT_CALL_VIRTUAL_METHOD();
}

PRIVATE void _shape_draw(void *self)
{
    ASSERT_CALL_VIRTUAL_METHOD();
}

struct _shape *shape_new(void)
{
    struct _shape *shape = calloc(1, sizeof(struct _shape));
    if(shape == NULL)
    {
        return NULL;
    }
    static struct _virtual_table vtb = {
        .area = (void (*)(void *self))_shape_area, 
        .draw = (void (*)(void *self))_shape_draw
    };
    shape->vtb = &vtb;
    return shape;
}

#define SUPER(self) (&(self)->shape)

#if 0
void shape_free(struct _shape * self)
{
    if (self != NULL)
    {
        free(self);
    }
}
#endif

struct _rect
{
    // super
    struct _shape shape;

    // attribute
    double width, height;

    // method
    // void (*area)(void *self);
    // void (*draw)(void *self);
};

void rect_area(struct _rect *self)
{
    printf("rect area = %0.2f\n", self->width * self->height);
}

void rect_draw(struct _rect *self)
{
    printf("rect draw\n");
}

struct _rect *rect_new(double width, double height)
{
    struct _rect *rect = calloc(1, sizeof(struct _rect));
    if (rect == NULL)
    {
        return NULL;
    }
    rect->width = width;
    rect->height = height;

    static struct _virtual_table vtb = {
        .area = (void (*)(void *self))rect_area,
        .draw = (void (*)(void *self))rect_draw
    };

    SUPER(rect)->vtb = &vtb;
    return rect;
}

struct _circle
{
    // super
    struct _shape shape;

    // attribute
    double radius;

    // method
    // void (*area)(void *self);
    // void (*draw)(void *self);
};

void circle_area(struct _circle *self)
{
    printf("circle area = %0.2f\n", 3.14 * self->radius * self->radius);
}
void circle_draw(struct _circle *self)
{
    printf("circle draw\n");
}

struct _circle *circle_new(double radius)
{
    struct _circle *circle = calloc(1, sizeof(struct _circle));
    if (circle == NULL)
    {
        return NULL;
    }
    circle->radius = radius;

    static struct _virtual_table vtb = {
        .area = (void (*)(void *self))circle_area,
        .draw = (void (*)(void *self))circle_draw,
    };

    SUPER(circle)->vtb = &vtb;
    return circle;
}

int main(int argc, char *argv[])
{
    struct _rect *rect = rect_new(4, 5);
    rect_area(rect);
    rect_draw(rect);

    struct _circle *circle = circle_new(3);
    circle_area(circle);
    circle_draw(circle);

    printf("------------------------------\n");
    shape_area(rect);
    shape_area(circle);

    shape_draw(rect);
    shape_draw(circle);

    printf("------------------------------\n");
    struct _shape *shape = (struct _shape *)rect_new(2,3);
    shape_area(shape);
    shape_draw(shape);

    struct _shape *shape2 = NULL;
    shape2 = (struct _shape *)circle;
    shape_area(shape2);
    shape_draw(shape2);


    printf("------------------------------\n");
    struct _shape *shape3 = shape_new();
    shape_area(shape3);
    shape_draw(shape3);

    return 0;
}