c++ 使用函数指针结构体改变类的虚函数表

#include <cstring>
#include <iostream>

class A {
public:
  virtual void vfoo_1() { std::cout << "a_vfoo_1\n"; }

  virtual void vfoo_2(long long a) {
    std::cout << "a_vfoo_2: " << a << std::endl;
  }

  virtual int vfoo_3(int a, int b) { return a + b; }
};

typedef void (*void_pfunc_void)();
typedef void (*void_pfunc_int)(long long);
typedef int (*int_pfunc_int_int)(int, int);

struct other_vtable {
  void_pfunc_void pf1;
  void_pfunc_int pf2;
  int_pfunc_int_int pf3;
};

void g_f1() { std::cout << "g_f1\n"; }

void g_f2(long long a) {
  ((A *)a)->vfoo_1();
  printf("%p\n", (void *)a);
  // std::cout << "g_f2: " << a << std::endl;
}

int g_f3(int a, int b) { return b * 10; }

int main(void) {
  A *a = new A;
  other_vtable *ovt = new other_vtable;
  ovt->pf1 = g_f1;
  ovt->pf2 = g_f2;
  ovt->pf3 = g_f3;

  void *ptr = a;
  printf("%p\n", a);

  a->vfoo_1();
  a->vfoo_2(10);
  printf("a->vfoo_3: %d\n", a->vfoo_3(2, 5));
  puts("-------------------------------");

  memcpy(ptr, &ovt, sizeof(void *));

  a->vfoo_1();
  a->vfoo_2(10);
  printf("a->vfoo_3: %d\n", a->vfoo_3(2, 5));

  int breakpoint = 0;

  return 0;
}