Question

所以，我的继承类将项目写入文件时遇到问题。我将发布一个代码示例，因为它有多个实例，并且不会将这些特定项写入文件。我不确定我做错了什么，它正在将父类中的所有内容写到文件中，但是来自子类的那些东西不会写。这部分已在每个子类中完成：

//Parameterized constructor signature
Hourly::Hourly(int e, string n, string a, string p, double w, double h) :MyEmployee(e, n, a, p)

这是没有标题的驱动程序。

string fileInput;
    string employCategory = "";
    const string HOURLY = "Hourly";
    const string SALARIED = "Salaried";
    int answer;
    int count = 0;
    const int ONE = 1;
    const int TWO = 2;
    const int ARRAY_SIZE = 4;
    MyEmployee* payroll[ARRAY_SIZE];
    ifstream myOpenFile;
    ofstream myWrittenFile;
    payroll[0] = new Hourly(1, "H. Potter", "Privet Drive", "201-9090", 40, 12.00);
    payroll[1] = new Hourly(3, "R. Weasley", "The Burrow", "892-2000", 40, 10.00);
    payroll[2] = new Salaried(2, "A. Dumbledore", "Hogwarts", "803-1230", 1200);
    payroll[3] = new Salaried(4, "R. Hagrid", "Hogwarts", "910-8765", 1000);
    cout << "This program has two options:\n1 - Create a data file\n2 - Read data from a file and print paychecks.";
    //This loop will test if the user's input is valid.
    do
    {
        //Here, the user will enter a value to be used to either print checks or write a file.
        cout << "\nPlease enter <1> to create a file or <2> to print checks: ";
        cin >> answer;
        //The user entered one, so we'll write a file.
        if (answer == ONE)
        {
            cin.sync();
            cin.clear();
            cout << "\nPlease enter in the name of the file you wish to write to. Please don't forget to add .txt to the end: ";
            getline(cin, fileInput);
            myWrittenFile.open(fileInput);
            for (int i = 0; i < ARRAY_SIZE; i++)
            {
                MyEmployee* empPtr = payroll[i];
                if (typeid(*empPtr) == typeid(Hourly))
                {
                    Hourly* empHPtr = static_cast<Hourly*>(empPtr);
                }
                else if (typeid(*empPtr) == typeid(Salaried))
                {
                    Salaried* empSPtr = static_cast<Salaried*>(empPtr);
                }
            }
            for (int i = 0; i < ARRAY_SIZE; i++)
            {
                payroll[i]->writeData(myWrittenFile);
            }
            myWrittenFile.close();
            cout << "\nData saved .....";
            for (int i = 0; i < ARRAY_SIZE; i++)
            {
                delete payroll[i];
                payroll[i] = NULL;
            }


}

这是父类的一部分，包括写入文件：

void MyEmployee::writeData(ofstream& out)
{
    out << empNum << "\n";
    out << name << "\n";
    out << address << "\n";
    out << phoneNum << "\n";
}

这是儿童班的一部分：

void Hourly::writeData(ofstream& out)
{
    out << hoursWorked << "\n";
    out << wage << "\n";
    MyEmployee::writeData(out);
}

Answer 1

似乎是因为您的writeData()函数未声明为虚拟。

当一个函数被声明为虚拟并在派生类中被覆盖时，它将在运行时计算必须精确调用的函数。（Virtual method tables）。

您的函数未声明为虚函数，因此从MyEmployee指针调用它，您调用writeData()类中定义的MyEmployee函数，而不是其派生类。这就是为什么它不会从派生类中写入任何数据的原因。

PS：

typeid(*empPtr) == typeid(Hourly)
typeid(*empPtr) == typeid(Salaried)

这些表达式始终为false。

继承的类不会写入文件

1 个答案: