从derived *到base *的转换存在但无法访问 [英] conversion from derived * to base * exists but is inaccessible

问题描述

为什么以下代码会产生此错误，即使c是结构并且默认情况下具有公共继承？

Why does the follwing code produce this error even though c is a struct and has a public inheritance by default??

struct c 
{
protected:
    int i;
public:
    c(int ii=0):i(ii){}
    virtual c *fun();
};

c* c::fun(){
    cout<<"in c";
    return &c();
}

class d : c
{
 public:
    d(){}
    d* fun()
    {
        i = 9;
        cout<<"in d"<<'\t'<<i;
        return &d();
    }
};


int main()
{
    c *cc;
    d dd;
    cc = &dd;
    cc->fun();
}

推荐答案

您需要：

class d : public c

class 默认情况下继承 private 。

当您私下从类或 struct 继承时，您明确说明了直接转换从派生类型到基类型是不可能的。

When you privately inherit from a class or a struct, you explicitly say, among others, that direct conversion from a derived type to a base type isn't possible.

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