C++多重继承 - 为什么你不工作？
我正在尝试找出一个有趣的多重继承问题。
祖父母是一个具有多个方法的接口类：
class A
{
public:
virtual int foo() = 0;
virtual int bar() = 0;
};
然后是部分完成该接口的抽象类。
class B : public A
{
public:
int foo() { return 0;}
};
class C : public A
{
public:
int bar() { return 1;}
};
我想要使用的类继承自两个父类，并通过 using 指令指定应该来自何处的方法：
class D : public B, public C
{
public:
using B::foo;
using C::bar;
};
当我尝试实例化 DI 时，会因尝试实例化抽象类而出现错误。
int main()
{
D d; //<-- Error cannot instantiate abstract class.
int test = d.foo();
int test2 = d.bar();
return 0;
}
有人可以帮助我理解这个问题以及如何最好地利用部分实现吗？
I am trying to figure out an interesting multiple inheritance issue.
The grandparent is an interface class with multiple methods:
class A
{
public:
virtual int foo() = 0;
virtual int bar() = 0;
};
Then there are abstract classes that are partially completing this interface.
class B : public A
{
public:
int foo() { return 0;}
};
class C : public A
{
public:
int bar() { return 1;}
};
The class I want to use inherits from both of the parents and specifies what method should come from where via using directives:
class D : public B, public C
{
public:
using B::foo;
using C::bar;
};
When I try to instantiate a D I get errors for trying to instantiate an abstract class.
int main()
{
D d; //<-- Error cannot instantiate abstract class.
int test = d.foo();
int test2 = d.bar();
return 0;
}
Can someone help me understand the problem and how to best make use of partial implementations?
如果你对这篇内容有疑问，欢迎到本站社区发帖提问 参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。
绑定邮箱获取回复消息
由于您还没有绑定你的真实邮箱，如果其他用户或者作者回复了您的评论，将不能在第一时间通知您！
发布评论
评论（2）
你没有钻石继承权。
D的B和C基类各有自己的A基类子对象，因为它们不是虚拟继承的来自A。因此，在
D中，实际上需要实现四个纯虚成员函数：A::foo和A::bar来自B以及来自C的A::foo和A::bar。您可能想使用虚拟继承。类声明和基类列表如下所示：
如果您不想使用虚拟继承，那么您需要重写
D中的其他两个纯虚函数：You don't have diamond inheritance. The
BandCbase classes ofDeach have their ownAbase class subobject because they do not inherit virtually fromA.So, in
D, there are really four pure virtual member functions that need to be implemented: theA::fooandA::barfromBand theA::fooandA::barfromC.You probably want to use virtual inheritance. The class declarations and base class lists would look like so:
If you don't want to use virtual inheritance then you need to override the other two pure virtual functions in
D:您需要将基类设为
虚拟，以便它们能够正确继承。一般规则是所有非私有成员函数和基类都应该是虚拟的，除非您知道自己在做什么并且想要禁用该成员/基类的正常继承。You need to make your base classes
virtualin order for them to inherit properly. The general rule is that all non-private member functions and base classes should bevirtualUNLESS you know what you're doing and want to disable normal inheritance for that member/base.