class A {
public:
virtual void fun0() { cout << "A::fun0" << endl; }
virtual void fun1() { cout << "A::fun1" << endl; }
int a;
int b;
};
int main(int argc, char* argv[])
{
A a;
cout << "Size of A = " << sizeof(a) << endl;
return 0;
}
结果如下:结果如下: Size of A = 4
虚函数的内存结构如下,你也可以通过函数指针,先找到虚函数表(VTABLE),然后访问每个函数地址来验证这种结构,在国外网站作者是:Zeeshan Amjad写的"ATL on the Hood中有详细介绍"
图二
4.我们再来看看继承中虚函数的内存结构,先看下面的例子
class A {
public:
virtual void f() { }
};
class B {
public:
virtual void f() { }
};
class C {
public:
virtual void f() { }
};
class Drive : public A, public B, public C {
};
int main() {
Drive d;
cout << "Size is = " << sizeof(d) << endl;
return 0;
}
结果如下:Size is = 12 ,相信大家一看下面的结构图就会很清楚,
图三
5.我们再来看看用虚函数实现多态性,先看个例子:
class A {
public:
virtual void f() { cout << "A::f" << endl; }
};
class B :public A{
public:
virtual void f() { cout << "B::f" << endl;}
};
class C :public A {
public:
virtual void f() { cout << "C::f" << endl;}
};
class Drive : public C {
public:
virtual void f() { cout << "D::f" << endl;}
};
int main(int argc, char* argv[])
{
A a;
B b;
C c;
Drive d;
a.f();
b.f();
c.f();
d.f();
return 0;
}
结果:A::f
B::f
C::f
D::f