具有 3 级继承的基类shared_ptr的多态性

Polymorphism with shared_ptr of base class with 3 level inheritance

本文关键字：ptr 多态性 shared 基类 继承 具有      更新时间：2023-10-16

>我有一个基类

class Base {
public:
virtual void func() = 0;
}

我有一个具体的派生类

class Derived : public Base {
public:
void func() {func2();}
void func2() {};
}

最后，我有一个派生类

class DerivedDerived : public Derived {
// inherits func() from Derived
void func2() {} //Overrides func2() from Derived
}
void g(shared_ptr<Base> s) {
s->func();
}

现在，我的问题是这样的：我有一个函数 g((，它接受一个 shared_ptr

并在没有任何类型转换的情况下调用 func((，因为它不知道任何子类。 现在，如果我这样做： 
shared_ptr<Base> s1 = make_shared<Derived>();
shared_ptr<Base> s2 = make_shared<DerivedDerived>();
g(s1); //func() of Derived Class called
g(s2); //func2() of Derived Class called inside, func2() of DerivedDerived Class needed to be called inside.

我希望 func(( 调用正确类的 func2((，即

作为本主题的补充，由于 C++11 存在override关键字，因此可以防止此类错误。使用它时，如果未重写使用该关键字的方法，则会引发编译器错误。

class DerivedDerived : public Derived {
void func2() {} override; // would throw an error in your case
}

好的，因为您已经更改了代码 - 正如 Jarod42 所提到的，我正在更新结果 - 您正在隐藏 func2 而不是覆盖它。我还根据亚历山大的建议添加了覆盖关键字。

#include <iostream>
#include <memory>
class Base {
public:
virtual void func() = 0;
};
class Derived : public Base {
public:
void func() override {func2();}
virtual void func2() {std::cout << "func2: Derivedn";};
}
;
class DerivedDerived : public Derived {
public:
void  func2() override {std::cout << "func2: DerivedDerivedn";} //Overrides func() from Derived
};
void g(std::shared_ptr<Base> s) {
s->func();
}
int main()
{
std::shared_ptr<Base> s1 = std::make_shared<Derived>();
std::shared_ptr<Base> s2 = std::make_shared<DerivedDerived>();
g(s1); //func() of Derived Class called
g(s2); //func() of Derived Class called, func() of DerivedDerived Class needed to
return 0;
}
/***************
Output:
$ ./test
func2: Derived
func2: DerivedDerived
***************/
/* Compiler error when override is used and func2 is not marked virtual
src/test.cpp:19:16: error: ‘void DerivedDerived::func2()’ marked ‘override’, but does not override
void  func2() override {std::cout << "func2: DerivedDerivedn";} //Overrides func() from Derived
*/
相关文章：