c++中公共继承、私有继承和受保护继承之间的区别是什么?
我在SO上找到的所有问题都是针对具体案例的。
c++中公共继承、私有继承和受保护继承之间的区别是什么?
我在SO上找到的所有问题都是针对具体案例的。
当前回答
我发现了一个简单的答案,所以我想把它贴出来,作为我未来的参考。
它来自http://www.learncpp.com/cpp-tutorial/115-inheritance-and-access-specifiers/的链接
class Base
{
public:
int m_nPublic; // can be accessed by anybody
private:
int m_nPrivate; // can only be accessed by Base member functions (but not derived classes)
protected:
int m_nProtected; // can be accessed by Base member functions, or derived classes.
};
class Derived: public Base
{
public:
Derived()
{
// Derived's access to Base members is not influenced by the type of inheritance used,
// so the following is always true:
m_nPublic = 1; // allowed: can access public base members from derived class
m_nPrivate = 2; // not allowed: can not access private base members from derived class
m_nProtected = 3; // allowed: can access protected base members from derived class
}
};
int main()
{
Base cBase;
cBase.m_nPublic = 1; // allowed: can access public members from outside class
cBase.m_nPrivate = 2; // not allowed: can not access private members from outside class
cBase.m_nProtected = 3; // not allowed: can not access protected members from outside class
}
其他回答
公共继承对IS-A关系建模。与
class B {};
class D : public B {};
每个D都是B。
私有继承为IS-IMPLEMENTED-USING关系建模(或者其他什么关系)。与
class B {};
class D : private B {};
D不是B,但每个D都在实现过程中使用了B。私有继承总是可以通过使用包含来消除:
class B {};
class D {
private:
B b_;
};
这个D也可以用B实现,在这种情况下使用它的b_。与继承相比,包含在类型之间的耦合不那么紧密,因此通常应该首选它。有时使用容器代替私有继承不像私有继承那样方便。这通常是懒惰的蹩脚借口。
我想没有人知道什么是受保护的继承模型。至少我还没看到任何令人信服的解释。
我发现了一个简单的答案,所以我想把它贴出来,作为我未来的参考。
它来自http://www.learncpp.com/cpp-tutorial/115-inheritance-and-access-specifiers/的链接
class Base
{
public:
int m_nPublic; // can be accessed by anybody
private:
int m_nPrivate; // can only be accessed by Base member functions (but not derived classes)
protected:
int m_nProtected; // can be accessed by Base member functions, or derived classes.
};
class Derived: public Base
{
public:
Derived()
{
// Derived's access to Base members is not influenced by the type of inheritance used,
// so the following is always true:
m_nPublic = 1; // allowed: can access public base members from derived class
m_nPrivate = 2; // not allowed: can not access private base members from derived class
m_nProtected = 3; // allowed: can access protected base members from derived class
}
};
int main()
{
Base cBase;
cBase.m_nPublic = 1; // allowed: can access public members from outside class
cBase.m_nPrivate = 2; // not allowed: can not access private members from outside class
cBase.m_nProtected = 3; // not allowed: can not access protected members from outside class
}
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 // 'private' is default for classes
{
// x is private
// y is private
// z is not accessible from D
};
重要提示:类B, C和D都包含变量x, y和z。这只是访问的问题。
关于受保护继承和私有继承的使用,你可以在这里阅读。
1)公共继承:
a.基类的私有成员在派生类中不可访问。
b.基类的受保护成员在派生类中仍然受保护。
c.基类的公共成员在派生类中保持为公共。
因此,其他类可以通过派生类对象使用基类的公共成员。
2)受保护遗产:
a.基类的私有成员在派生类中不可访问。
b.基类的受保护成员在派生类中仍然受保护。
c.基类的公共成员也成为派生类的受保护成员。
因此,其他类不能通过派生类对象使用基类的公共成员;但它们可用于派生的子类。
3)私人继承:
a.基类的私有成员在派生类中不可访问。
b.基类的Protected & public成员变成派生类的private成员。
因此,基类的成员不能被其他类通过派生类对象访问,因为它们在派生类中是私有的。甚至是Derived的子类 类不能访问它们。
Accessors | Base Class | Derived Class | World
—————————————+————————————+———————————————+———————
public | y | y | y
—————————————+————————————+———————————————+———————
protected | y | y | n
—————————————+————————————+———————————————+———————
private | | |
or | y | n | n
no accessor | | |
y: accessible
n: not accessible
基于这个例子的java…我认为一张小桌子胜过千言万语:)