Question

我有user class，其成员指针指向data class。但是我希望实现一个扩展derivedUser的{{1}}，但它还需要存储在user中的其他数据，它看起来像这样：

derivedData class

但问题在于：按照我设置的方式，class Data { /*...the stored data...*/ } class DerivedData : public Data { /*...the additional data...*/ } class User { public: /*...some methods that use dp...*/ protected: Data* dp; } class DerivedUser : public User { public: /*...even more methods that use ddp...*/ protected: DerivedData* ddp; }将存储指向同一对象的两个不同类型的指针，这不是最佳的。 DerivedUser class应该只存储一个指针，它应该知道它是DerivedUser类型，如果给出错误类型的数据则会失败。问题是：我该如何实现这个？

我试过了：

DerivedData

Answer 1

在DerivedUser类

中添加方法DerivedData* GetData()

DerivedData* GetData() { return static_cast<DerivedData>(dp); }

如果DerivedUser的构造函数如下所示，您可以确保dp为DerivedData*：

DerivedUser(DerivedData* d):User(d){}

以下是完整代码：

class Data {
    /*...the stored data...*/
}

class DerivedData : public Data {
    /*...the additional data...*/
}

class User {

    public:
        User(Data* d):dp(d){}
        /*...some methods that use dp...*/

    protected:
        Data* dp;
}

class DerivedUser : public User {

    public:
        DerivedUser(DerivedData* d):User(d){}
        /*...even more methods that use ddp...*/

    protected:
        DerivedData* GetData(void)
        {
            return static_cast<DerivedData*>(dp);
        };
}

Answer 2

我看到你希望DerivedUser在其构造函数中包含DerivedData。

由于多态性，父类可以引用它的子类。所以这是合法的：

Data* dp = new DerivedData();

以下是您正在寻找的解决方案：

class User {

public:
    /*...some methods that use dp...*/

    User(Data* dp){
        this->dp = dp;
    }

protected:
    Data* dp;
};

class DerivedUser : public User {

public:
    /*...even more methods that use ddp...*/

    DerivedUser(DerivedData *dp) : User(dp) {

    }
};

现在，DerivedUser指向您的DerivedData类

这里：

int main(){

    DerivedData* dp = new DerivedData();

    DerivedUser* user = new DerivedUser(dp);


    return 0;
}

c ++派生类更改基类指针

2 个答案: