Access specifier

在C++中access specifier可以用于2处，一是在定义类成员的时候，还有就是在类继承的时候

class Base
{
public:
int m_a;
protected:
int m_b;
private:
int m_c;

public:
void foo()
{
Base b;
b.m_c = 0; // notice here is OK
b.m_b = 0; // notice here is OK
b.m_a = 0;
}

};

class Public:public Base
{
public:
void foo()
{
m_a = 0;
m_b = 0;
//m_c = 0; // m_c is private in Base, so it's not visible to Public
}
};

对于类中的修饰符我们对于其含义一般都很了解。但是对于在继承时的access specifier就有时候会有些搞不清楚，原因也是因为使用的较少。
下面用一张表格来对他们进行总结：

Public inheritance

Base access specifier	Derived access specifier	Derived class access?	Public access?
Public	Public	Yes	Yes
Private	Private	No	No
Protected	Protected	Yes	No

Protected inheritance

Base access specifier	Derived access specifier	Derived class access?	Public access?
Public	Protected	Yes	No
Private	Private	No	No
Protected	Protected	Yes	No

Private inheritance

Base access specifier	Derived access specifier	Derived class access?	Public access?
Public	Private	Yes	No
Private	Private	No	No
Protected	Private	Yes	No