如果只是这样实现，那么无法多态。即给父类赋值子类，然后调用父类，实测还是调用的父类接口。因此添加虚函数表

CMakelists.txt

@@ -50,10 +50,10 @@ install(TARGETS demo DESTINATION bin)
 install (FILES "${PROJECT_BINARY_DIR}/config.h"
         DESTINATION include)
 
-# 4. 启用测试
-enable_testing()
-# 测试程序是否成功运行
-add_test (NAME test_demo COMMAND demo 1 2 3 5 8)
+# # 4. 启用测试
+# enable_testing()
+# # 测试程序是否成功运行
+# add_test (NAME test_demo COMMAND demo 1 2 3 5 8)
 
 # 5. 支持GDB
 set(CMAKE_BUILD_TYPE "Debug")

main.c

@@ -3,28 +3,66 @@
 #include <stdio.h>
 #include <stdbool.h>
 #include <stdlib.h>
+#include <assert.h>
+
+#define VIRTUAL  
+#define PRIVATE  
+
+struct _virtual_table
+{
+    VIRTUAL void (*area)(void *self);
+    VIRTUAL void (*draw)(void *self);
+};
+
+void virtual_area(void *self)
+{
+    assert(!"can't call abstract method");
+}
+
+void virtual_draw(void *self)
+{
+    assert(!"can't call abstract method");
+}
+
+struct _virtual_table *virtual_new(void)
+{
+    struct _virtual_table *v = calloc(1, sizeof(struct _virtual_table));
+    if (v == NULL)
+    {
+        return NULL;
+    }
+    v->area = virtual_area;
+    v->draw = virtual_draw;
+    return v;
+}
+
 
-#define VIRTUAL
 
 struct _shape
 {
-    VIRTUAL void (*area)(struct _shape *self);
-    VIRTUAL void (*draw)(struct _shape *self);
+    VIRTUAL void (*area)(void *self);
+    VIRTUAL void (*draw)(void *self);
 };
 
-void shape_area(struct _shape *self)
+void shape_area(void *self)
 {
-    printf("shape area\n");
+    assert(!"can't call abstract method");
 }
 
-void shape_draw(struct _shape *self)
+void shape_draw(void *self)
 {
-    printf("shape draw\n");
+    assert(!"can't call abstract method");
 }
 
 struct _shape *shape_new(void)
 {
     struct _shape *shape = calloc(1, sizeof(struct _shape));
+    if(shape == NULL)
+    {
+        return NULL;
+    }
+    shape->area = shape_area;
+    shape->draw = shape_draw;
     return shape;
 }
 
@@ -38,17 +76,19 @@ void shape_free(struct _shape * self)
 }
 #endif
 
+#define SUPER(self) ((self)->shape)
+
 struct _rect
 {
     // super
-    // struct _shape shape;
+    struct _shape* shape;
 
     // attribute
     double width, height;
 
     // method
-    void (*area)(struct _rect *self);
-    void (*draw)(struct _rect *self);
+    // void (*area)(void *self);
+    // void (*draw)(void *self);
 };
 
 void rect_area(struct _rect *self)
@@ -71,22 +111,28 @@ struct _rect *rect_new(double width, double height)
     rect->width = width;
     rect->height = height;
 
-    rect->area = rect_area;
-    rect->draw = rect_draw;
+    rect->shape = shape_new();
+    if (rect->shape == NULL)
+    {
+        return NULL;
+    }
+
+    SUPER(rect)->area = (void (*)(void *self))rect_area;
+    SUPER(rect)->draw = (void (*)(void *self))rect_draw;
     return rect;
 }
 
 struct _circle
 {
     // super
-    // struct _shape shape;
+    struct _shape *shape;
 
     // attribute
     double radius;
 
     // method
-    void (*area)(struct _circle *self);
-    void (*draw)(struct _circle *self);
+    // void (*area)(void *self);
+    // void (*draw)(void *self);
 };
 
 void circle_area(struct _circle *self)
@@ -105,22 +151,38 @@ struct _circle *circle_new(double radius)
     {
         return NULL;
     }
+    circle->shape = shape_new();
+    if (circle->shape == NULL)
+    {
+        return NULL;
+    }
+
     circle->radius = radius;
 
-    circle->area = circle_area;
-    circle->draw = circle_draw;
+    SUPER(circle)->area = (void (*)(void *self))circle_area;
+    SUPER(circle)->draw = (void (*)(void *self))circle_draw;
     return circle;
 }
 
 int main(int argc, char *argv[])
 {
     struct _rect *rect = rect_new(4, 5);
-    rect->area(rect);
-    rect->draw(rect);
+    rect_area(rect);
+    rect_draw(rect);
 
     struct _circle *circle = circle_new(3);
-    circle->area(circle);
-    circle->draw(circle);
+    circle_area(circle);
+    circle_draw(circle);
+
+    // struct shape *shape = shape_new();
+    // shape_area(shape);
+    // shape_draw(shape);
+
+    // struct _shape *shape = NULL;
+    struct _shape *shape = rect_new(2,3);
+    // shape = rect;
+    shape_area(shape);
+    shape_draw(shape);
 
     return 0;
 }

mk.bat

@@ -1,6 +1,8 @@
 @REM D:\Lang\cmake-3.27.5-windows-x86_64\bin\cmake.EXE --no-warn-unused-cli -DCMAKE_BUILD_TYPE:STRING=Debug -DCMAKE_EXPORT_COMPILE_COMMANDS:BOOL=TRUE -DCMAKE_C_COMPILER:FILEPATH=D:\Software\mingw64\bin\gcc.exe -DCMAKE_CXX_COMPILER:FILEPATH=D:\Software\mingw64\bin\g++.exe -SF:/OpenDemo/1_vsc_cmake -Bf:/OpenDemo/1_vsc_cmake/build -G "MinGW Makefiles"
 @REM cmake -Bbuild -G "Visual Studio 17 2022"
 
+del ".\\build\\release\\bin\\demo.exe"
+
 cmake -B build -G "MinGW Makefiles"
 
 make -C build
@@ -10,4 +12,4 @@ make -C build test
 @REM cpack -C ./build/CPackConfig.cmake
 @REM cpack -C ./build/CPackSourceConfig.cmake
 
-"build/release/bin/demo.exe"
+".\\build\\release\\bin\\demo.exe"