container_of是谁发明的，真是个天才！！！

library/common.h

@@ -7,5 +7,18 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <assert.h>
+#include <stdarg.h>
+
+// [warring] offsetof is redefined in stddef.h
+// 
+// #define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
+// #define container_of(ptr, type, member) ({ \
+//     const typeof( ((type *)0)->member ) *__mptr = (ptr); \
+//     (type *)( (char *)__mptr - offsetof(type,member) );})
+
+#define _offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
+#define container_of(ptr, type, member) ({ \
+    const typeof( ((type *)0)->member ) *__mptr = (ptr); \
+    (type *)( (char *)__mptr - _offsetof(type,member) );})
 
 #endif

library/copper.c

@@ -58,6 +58,8 @@ struct _copper_cash *copper_cash_new(double width, double height, double radius)
     {
         return NULL;
     }
+    cc->self = cc;
+
     cc->price = 100;
     // set parent
     cc->shape = shape;

library/copper.h

@@ -9,6 +9,8 @@
 
 struct _copper_cash
 {
+    struct _copper_cash *self;
+
     struct _shape *shape;
     struct _rect *rect;
     struct _circle *circle;

library/rect.c

@@ -11,8 +11,11 @@ double rect_area(void *self, void *parent)
 
 void rect_draw(void *self, void *parent)
 {
-    struct _rect *pthis = (struct _rect *)parent;
+    // struct _rect *pthis = (struct _rect *)parent;
-    pthis->shape->vtb.draw(self, NULL);
+    // pthis->shape->vtb.draw(self, NULL);
+
+    struct _rect *pthis = container_of(parent, struct _rect, self);
+    pthis->shape->vtb.draw(pthis, NULL);
 }
 
 double _rect_area(void *self, void *parent)
@@ -50,6 +53,8 @@ struct _rect *rect_new(double width, double height)
     {
         return NULL;
     }
+    rect->self = rect;
+
     rect->width = width;
     rect->height = height;
     // set parent

library/rect.h

@@ -7,7 +7,8 @@
 
 struct _rect
 {
-    int invalid;
+    // int invalid;
+    struct _rect *self;    
 
     // super
     struct _shape *shape;

library/shape.c

@@ -56,6 +56,8 @@ struct _shape *shape_new(void)
     {
         return NULL;
     }
+    shape->self = shape;
+
     static struct _virtual_table vtb = {
         .area = (double (*)(void *self, void *parent))_shape_area, 
         .draw = (void (*)(void *self, void *parent))_shape_draw

library/shape.h

@@ -17,6 +17,8 @@ struct _virtual_table
 
 struct _shape
 {
+    struct _shape *self;
+    
     struct _virtual_table vtb;
 };