Question

我正在尝试编写此代码，其中有两个类从父类继承。但是当我尝试在链接列表中使用它时，此代码会中断。这是代码

class airship{

public:
    airship(){};
//  virtual ~ airship();
    virtual void setData (string)=0;
    virtual void showData()=0;
    void setNext(airship* newptr);
    airship* getNext();
    void setType(int n){airshipType=n;}
    int getType(){return airshipType;}
    void setCount(int n){maxPassengerCount=n;};
    int getCount(){return maxPassengerCount;}
    void setWeight(int n){maxCargoWeight=n;}
    int getWeight(){return maxCargoWeight;}

protected:
    int maxPassengerCount;
    int maxCargoWeight;
    int airshipType;

private:
    airship* next;
};

class airplane: public airship{

protected:

    const char* airplaneName;
    int engineType;
    double range;

public:
    airplane():airship(){};
//  ~ airplane();
    void setData(string);
    void showData();
    void setEngine(int n){engineType=n;}
    int getEngine(){return engineType;}
    void setRange(int n){range=n;}
    int getRange();

};

class balloon : public airship{

protected:
    const char* balloonName;
    int gasType;
    double maxAltitude;

public:
    balloon():airship(){};
//  ~balloon();
    void setData(string);
    void showData();
    void setGas(int);
    int getGas();
    void setAlt(int);
    int getAlt();

};

class mylist{

private:
    airship* headAirship;
public:
    void createlist(fstream&);
    void setAirship(airship* Node){Node=headAirship;}
    airship* getAirship(){return headAirship;}
};

void airship::setNext(airship* Node)
{
    this->next=Node;
}

void airplane::setData(string line)
{
    string line1;
    bool flag=true;
    int npos=0,nend,count=0;
    while(line.c_str()!=NULL && flag)
    {
        nend=line.find(",",npos);

        if (nend!=-1)
        {
            line1=line.substr(npos,nend);
        }
        else
        {
            line1=line;
            flag=false;
        }
        line=line.substr(nend+1,line.length());

        if (count==0)
            this->airshipType=atoi(line1.c_str());
        else if(count==1)
            this->airplaneName=line1.c_str();
        else if(count==2)
            this->maxPassengerCount=atoi(line1.c_str());
        else if(count==3)
            this->maxCargoWeight=atoi(line1.c_str());
        else if(count==4)
            this->engineType=atoi(line1.c_str());
        else
            this->range=atoi(line1.c_str());

        count=count+1;
    }
}

void balloon::setData(string line)
{
    string line1;
        bool flag=true;
        int npos=0,nend,count=0;
        while(line.c_str()!=NULL && flag)
        {
            nend=line.find(",",npos);

            if (nend!=-1)
            {
                line1=line.substr(npos,nend);
            }
            else
            {
                line1=line;
                flag=false;
            }
            line=line.substr(nend+1,line.length());

            if (count==0)
                this->airshipType=atoi(line1.c_str());
            else if(count==1)
                this->balloonName=line1.c_str();
            else if(count==2)
                this->maxPassengerCount=atoi(line1.c_str());
            else if(count==3)
                this->maxCargoWeight=atoi(line1.c_str());
            else if(count==4)
                this->gasType=atoi(line1.c_str());
            else
                this->maxAltitude=atoi(line1.c_str());

            count=count+1;
        }

}

void mylist::createlist(fstream &myfile)
{

    string ipdata;
    int type;

    while (getline(myfile,ipdata))
    {
            airship* newNode;
            type=ipdata.find(",",0);
            string ch=ipdata.substr(type-1,type);
            if (atoi(ch.c_str())==0)
            {
                airplane* planeNode=new airplane();
                planeNode->setData(ipdata);
                newNode=planeNode;
            }
            else
            {
                balloon* balloonNode=new balloon();
                balloonNode->setData(ipdata);
                newNode=balloonNode;
            }
            newNode->setNext(headAirship);
            this->headAirship=newNode;

    }


}


int main()
{
    mylist* list=0;
    airship* firstNode=0,*otherNode=0;

    /*if(argv[1]==NULL)
    {   
        cout<<"File not Found"<<endl;
        return -1;      
    }*/

    fstream ipFile("data.txt",ios::in | ios::out);

    if(ipFile.is_open())
    {
        list->createlist(ipFile);
    }

    list->setAirship(firstNode);


    return 0;
}

airplane :: setdata（string）函数无法正常工作，并且无法在createList函数中检测headAirship指针。这就是为什么当我尝试执行此操作时，我在createlist函数中出现内存异常错误的原因：newNode-＆GT; setNext（headAirship）;

Assignment4Solution2.exe中0x00912ae0处的未处理异常：0xC0000005：
访问冲突读取位置0x00000000。

Answer 1

我认为问题在于：

mylist* list=0;

在该行中，您创建了一个指向 myList 对象的指针，但是您没有指向任何此类对象;它指向地址0

然后你做

list->createlist(ipFile);

由于list没有指向包含 myList 对象的地址，因此调用任何myList方法都会产生您观察到的错误：访问冲突读取位置0x00000000。

相反，当您创建列表指针时，调用myList的构造函数以便创建对象并初始化指针以指向它

myList * list = new myList();

希望有所帮助：）

尝试分配值时，继承的C ++代码会中断

1 个答案: