Question

我试图从类中保存一个Object。当我添加新记录（添加要保存的新对象）时，先前的记录将被删除。我究竟做错了什么？似乎一旦我添加了一个新对象，之前创建的对象就会因为idk而被删除。一直试着这几个小时。似乎无法弄明白。

void Department2File(HANDLE screen, Department &Departments, int deptcount)
{
    Department Testing;
    fstream file;
    file.open("Departmentsdata.dat", ios::out | ios::binary);
    file.close();
    file.open("Departmentsdata.dat", ios::in | ios::out | ios::binary);

    if (!file)
    {
        cout << "Error opening file.";
    }

    // writting data
    long size = (deptcount * sizeof(Departments));

    if (deptcount == 0)
    {
        size = (deptcount * sizeof(Departments));
    }
    else
    {
        size = (deptcount * sizeof(Departments))+1;
    }

    cout << "\nsaved!" << endl;;
    file.clear();
    file.seekp(size, ios::beg);
    file.write(reinterpret_cast <char *>(&Departments), sizeof(Departments));
    file.clear();
    file.seekg(size, ios::beg);
    file.read(reinterpret_cast<char *> (&Testing), sizeof(Departments));


    cout << Testing.DepartmentID;////////////<--------------delete

    ///////////////////////////////
    ///////////////DELETE//////////
            file.clear();
            file.seekg(0, ios::beg);
            file.get(reinterpret_cast<char *> (&Testing), sizeof(Departments));
            cout <<"\n RECORD 0: "<<Testing.DepartmentID;

                                    ////////////////////////////
    file.close();

}

Answer 1

在ios::app函数中添加标记open，以在文件末尾添加输出：

file.open("Departmentsdata.dat", ios::out | ios::app | ios::binary);

点击此链接：http://www.cplusplus.com/doc/tutorial/files/

更新：尝试在代码中只使用一个：

fstream file;
file.open("Departmentsdata.dat", ios::out | ios::binary);
file.close();
file.open("Departmentsdata.dat", ios::in | ios::out | ios::binary);

像这样：

fstream file;
file.open("Departmentsdata.dat", ios::in | ios::app | ios::out | ios::binary);
//Write Something
file.close();

但这取决于你想要做什么。

C ++ Previous Record在编写新对象时被删除

1 个答案: