类成员访问权限
class Base
{
private:
int a;
public:
int b;
void foo()
{
cout << a << b << d << endl; //OK: 类体内可以访问任何private、public、protected成员
}
protected:
int d;
};
class Derived1: public Base
{
public:
void get()
{
cout << b << d << endl; //OK: 继承类可以访问基类的public、protected成员
cout << a << endl; //错误:继承类不能访问private成员
}
};
int main()
{
Base b;
cout << b.a << endl; //错误:实例化对象不能访问private成员
cout << b.d << endl; //错误:实例化对象不能访问protected成员
cout << b.b << endl; //OK:实例化对象能访问public成员
}
继承时的访问权限
派生类只能访问基类的public和protected成员,而这两个成员在派生类中的新的访问权限由继承关系确定:
继承关系 | public变为… | protected变为… |
---|---|---|
public | public | protected |
protected | protected | protected |
private | private | private |
class Base
{
private:
int a;
public:
int b;
protected:
int d;
};
class Derived1: public Base
{
};
class Derived2: protected Base
{
};
class Derived3: private Base
{
};
int main()
{
Derived1 d1;
cout << d1.b << endl; //OK: b在Derived1还是public
cout << d1.d << endl; //错误: d在Derived1是protected
Derived2 d2;
cout << d2.b << endl; //错误: b在Derived2是protected
cout << d2.d << endl; //错误: d在Derived2是protected
Derived3 d3;
cout << d3.b << endl; //错误: b在Derived3是private
cout << d3.d << endl; //错误: d在Derived3是private
}