Question

我一直试图将整个结构数据保存到文件中，然后从文件中读取，您可以在我的代码中看到我正在将数据写入struct（由用户输入），然后将其保存到使用myFile.write函数保存对象的文件

如下面的代码所示，当程序第一次运行时，我再次输入菜单后又输入数据，然后按2加载数据，它可以正常工作并成功加载数据（我认为）。返回菜单，然后按3并显示我创建的所有航班（显然是因为数据当前位于主内存中，并且尚未由文件准备好）

    //Global Variables
    string savedFlight = "airportsDB\\SavedFlights.txt"; //path
    const unsigned short NUMBER_OF_AIRPORTS = 8;
    int gFlightSize=0;
    ifstream rFlightData;
    ofstream wFlightData;
    //SKipped some part
    struct flight {
    airport depature;
    airport arrival;
    double crsAlt;
    double distance;
    double fuel;
    void flight::createFlight();
    void flight::showFlight();
};

    void flight::createFlight() {
            cout << "Please insert depature airport (ICAO) : ";
            cin>>depature.icao;

        if(searchapt(depature.icao)){
            cout << "Please insert arrival airport (ICAO) : ";
            cin>>arrival.icao;

                if(searchapt(arrival.icao)){
                    cout<<"Enter Cruise Altitude [3000<Altitude<50000]  : ";
                    cin>>crsAlt;

                    if(crsAlt>50000 || crsAlt<3000){
                    cout<<"Unable CruiseAltitude Please put DIGITS* between 50,000ft and 3,000ft ";
                    }
                    else{
                        //CNTINUE HERE
                    }
            }

            else{
            cout<<"Arrival Airport Does Not Exist In DataBase";
            }
        }
        else{
            cout<<"Departure Airport Does Not Exist In DataBase";
        }
}

    void flight::showFlight(){
                        cout<<"\n Departure Airport : "<<depature.icao
                        <<"\n Arrival   Airport : "<<arrival.icao
                        <<"\n Cruise Altitude   : "<<crsAlt
                        <<"\n\n__________________________________________________\n\n";
    }

    //(Skipped some part)
        void writeFlightData(){
        int i=gFlightSize;
        cout<<"How many flights do you want to add : ";
        cin>>gFlightSize;
        saveCounter(gFlightSize);

    flights=new flight[gFlightSize];

    wFlightData.open(savedFlight,ios::app);

    textColor(12);
    cout<<"USE UPPERCASE LETTER !\n";
    textColor(15);

    while(i<gFlightSize){
            flights[i].createFlight();
            wFlightData.write((char *)&flights[i], sizeof(flights[i]));
            i++;
    }
    wFlightData.close();
}

void loadFlightData(){

    rFlightData.open(savedFlight);// , ios::in); // open file for reading

    cout << "  Loading Saved flights from disk";
    for(int i=3;i>0;i--){ //REVERSE LOOP FOR A TWIST
                cout<<" . ";
                Sleep(800);
            }
    cls 

    if(rFlightData.fail()){
        cout << "\nAn error occured while loading Saved Flights from disk .The file is corrupt or does not exist on the specified path\n\a"<<"\n Press any key to go back to the menu";
        saveCounter(0);
        _getch();
        cls
    }
    else{   

        Sleep(1000);
        for (int i = 0; i < gFlightSize; i++) {
            rFlightData.read((char *)&flights[i], sizeof(flights[i])); // read an object from a file
        }
        cout<<"  Data Load Successfull!  ";
        rFlightData.close(); // close the file
    }
}

我正在保存一个加法计数器，该计数器在程序再次启动时会读取，并且知道我添加的航班数量

现在的问题是，当我关闭该程序并再次运行并按2加载数据时，它不会加载数据，但会崩溃并给出异常错误“无效的空指针”

* 调试断言失败！程式C：\ Windows \ SYSTEM32 \ MSVCP110D.dll 文件：f \ dd \ vctools \ crt_bld \ self_x86_ \ crt \ src \ istream 线：734

表达式：无效的空指针

有关如何...的信息（按“重试”以调试应用程序）

*

Answer 1

我自己解决了这个问题，对不起，这个问题还不清楚。这是一个逻辑错误，因为我使用的是动态结构数组在尝试加载数据时类似地从用户那里获取数据时，我没有为指针分配新的动态位置，可以在该位置创建结构数组，然后将数据加载到程序中的结构中，所以我要做的就是写

flights=new flight[gFlightSize];

在这样的loaddata函数中，因此在加载动态位置之前，可以在主内存中将动态位置分配给可以将数据加载到

的结构

void loadFlightData(){
flights=new flight[gFlightSize];
rFlightData.open(savedFlight);// , ios::in); // open file for reading

cout << "  Loading Saved flights from disk";
for(int i=3;i>0;i--){ //REVERSE LOOP FOR A TWIST
            cout<<" . ";
            Sleep(800);
        }
cls 

if(rFlightData.fail()){
    cout << "\nAn error occured while loading Saved Flights from disk .The file is corrupt or does not exist on the specified path\n\a"<<"\n Press any key to go back to the menu";
    saveCounter(0);
    _getch();
    cls
}
else{   

    Sleep(1000);
    for (int i = 0; i < gFlightSize; i++) {
        rFlightData.read((char *)&flights[i], sizeof(flights[i])); // read an object from a file
    }
    cout<<"  Data Load Successfull!  ";
    rFlightData.close(); // close the file
}
}

exception：加载文件中保存的对象时无效的nulll指针

1 个答案: