C++之继承类中的this指针

#include<iostream>
#include<typeinfo>
using namespace std;

class A {
public:
A() {
cout << this << endl;
cout << typeid(this).name() << endl;
cout << "&a = " << &a << endl;
cout << "----------------------" << endl;
}
int a;
};
class B:public A {
public:
B() {
cout << this << endl;
cout << typeid(this).name() << endl;
cout << "&a = " << &a << endl;
cout << "&b = " << &b << endl;
cout << "----------------------" << endl;
}
int b;
};
class C :public B {
public:
C() {
cout << this << endl;
cout << typeid(this).name() << endl;
cout << "&a = " << &a << endl;
cout << "&b = " << &b << endl;
cout << "&c = " << &c << endl;
cout << "----------------------" << endl;
}
int c;
};

int main() {
A *pa = new C;
delete pa;

system("pause");
return 0;
}

输出结果：



可以看到A B C 的this指针的地址都是相同的（与成员变量a的地址相同），但类型是不同的。

如果A是抽象类呢：

#include<iostream>
#include<typeinfo>
using namespace std;

class A {
public:
A() {
cout << this << endl;
cout << typeid(this).name() << endl;
cout << "&a = " << &a << endl;
cout << "----------------------" << endl;
}
virtual void fun() = 0;
int a;
};
class B:public A {
public:
B() {
cout << this << endl;
cout << typeid(this).name() << endl;
cout << "&a = " << &a << endl;
cout << "&b = " << &b << endl;
cout << "----------------------" << endl;
}
void fun() {}
int b;
};
class C :public B {
public:
C() {
cout << this << endl;
cout << typeid(this).name() << endl;
cout << "&a = " << &a << endl;
cout << "&b = " << &b << endl;
cout << "&c = " << &c << endl;
cout << "----------------------" << endl;
}
int c;
};

int main() {
A *pa = new C;
delete pa;

system("pause");
return 0;
}

输出结果：



可以看到A B C 的this指针的地址都是相同的，但这里不再等于成员变量a的地址，应该是多了一个虚函数指针，偏移了4个字节，所以成员变量a的地址在this指针的基础上又加了4个字节，同样类型不相同。