Public, Protected and Private

原文 : http://stackoverflow.com/questions/860339/difference-between-private-public-and-protected-inheritance

class A 
{
public:
    int x;
protected:
    int y;
private:
    int z;
};

class B : public A
{
    // x is public
    // y is protected
    // z is not accessible from B
};

class C : protected A
{
    // x is protected
    // y is protected
    // z is not accessible from C
};

class D : private A
{
    // x is private
    // y is private
    // z is not accessible from D
};

IMPORTANT NOTE: Classes B, C and D all contain the variables x, y and z. It is just question of access.
About usage of protected and private inheritance you could read here.

原文 : http://www.programiz.com/cpp-programming/public-protected-private-inheritance

Summary of Public, Protected and Private Inheritance

Accessibility in Public Inheritance

Accessibility	private	protected	public
Accessible from own class?	yes	yes	yes
Accessible from dervied class?	no	yes	yes
Accessible outside dervied class?	no	no	yes

 

Accessibility in Protected Inheritance

Accessibility	private	protected	public
Accessible from own class?	yes	yes	yes
Accessible from dervied class?	no	yes	yes
Accessible outside dervied class?	no	no	no

 

Accessibility in Private Inheritance

Accessibility	private	protected	public
Accessible from own class?	yes	yes	yes
Accessible from dervied class?	no	yes	yes
Accessible outside dervied class?	no	no	no