C++虚函数表地址偏移

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Nirvana柒 2022-07-08 10:03:43 博主文章分类：C/C++ ©著作权

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#include <bits/stdc++.h>
using namespace std;

class Base {
public:
  Base() {
    cout << "Base构造" << endl;
  }
  virtual ~Base() {
    cout << "Base虚析构" << endl;
  }
  virtual void f1() {
    cout << "Base::f1()" << endl;
  }
  void f2() {
    cout << "Base::f2()" << endl;
  }
  virtual void f3() {
    cout << "Base::f3()" << endl;
    //cout << data << endl; 
  }
  int data = 5;
  static void fn() {
  }
};

int main() {
  cout << sizeof(Base) << endl;

  Base* p1 = new Base();
  Base* p2 = new Base();
  cout << p1->fn << endl;    // 静态成员函数可以直接获取地址
  cout << Base::fn << endl;  // 静态成员函数可以直接获取地址

//  cout << &Base::f1 << endl;  // 编译器将void(__thiscall A::*)()类型转换为bool类型
  printf("Base::f1()地址:%p\n", &Base::f1);
  printf("Base::f1()地址:%p\n", &Base::f1);
  printf("Base::f2()地址:%p\n", &Base::f2);
  printf("Base::fn()地址:%p\n", &Base::fn);

  cout << "p1对象地址: " << (p1) << endl;
  cout << "p1虚函数表首地址: " << (int*)(p1) << endl;
  cout << "p1虚函数表中第1个虚函数地址: " << (int*)*(int*)(p1) << endl;
  cout << "p1虚函数表中第2个虚函数地址: " << ((int*)*(int*)(p1)+1) << endl;
  cout << "p1虚函数表中第3个虚函数地址: " << ((int*)*(int*)(p1)+2) << endl;
  cout << "p1虚函数表中第4个虚函数地址: " << ((int*)*(int*)(p1)+3) << endl;


  cout << "p2对象地址: " << (p2) << endl;
  cout << "p2虚函数表首地址: " << (int*)(p2) << endl;
  cout << "p2虚函数表中第1个虚函数地址: " << (int*)*(int*)(p2) << endl;
  cout << "p2虚函数表中第2个虚函数地址: " << ((int*)*(int*)(p2)+1) << endl;
  cout << "p2虚函数表中第3个虚函数地址: " << ((int*)*(int*)(p2)+2) << endl;
  cout << "p2虚函数表中第4个虚函数地址: " << ((int*)*(int*)(p2)+3) << endl;

  cout << endl;

  typedef void(*PFUN)();

  PFUN pfBase = (PFUN) * ((int*)*(int*)p1 + 0);  // 析构
  PFUN pf1 = (PFUN) * ((int*)*(int*)p1 + 1);  // f1
  PFUN pf2 = (PFUN) * ((int*)*(int*)p1 + 2);  // f2
  PFUN pfnull = (PFUN) * ((int*)*(int*)p1 + 3);  //0x00
  pf1();
  pf2();  // 如果函数中有类成员变量，这样调用会出错。普通变量不会。和this指针有关。

}