如何使用C ++在向量中成功写入.DAT文件内容？

Question

I'm trying to write to a .DAT file my list of saved patients that are stored in a vector named PatientsInSystem. However, it won't work for some reason. Does anyone know what I might be doing wrong?

if (!PatientsInSystem.empty()) {
            cout << "Error. There are still patients checked in. They must be checked out before quitting." << endl;
            cout << "Printing remaining patients in the system... " << endl;
            for (int i = 0; i < PatientsInSystem.size(); i++) {
                cout << "Patient's ID: " << PatientsInSystem.at(i)->getID() << endl;
                cout << "Patient's Name: " << PatientsInSystem.at(i)->getFirstName() << " " << PatientsInSystem.at(i)->getLastName() << endl;
                cout << "Patient's Birthday: " << PatientsInSystem.at(i)->getBirthDate() << endl;
                cout << "Patient's Primary Doctor's ID: " << PatientsInSystem.at(i)->getPrimaryDoctorID() << endl;
            }
        }
        else {
            outFile.open("CurrentPatients.dat", ios::out | ios::binary);
            if (!outFile.is_open()) {
                cout << "File not open." << endl;
            }
            else {
                cout << "Binary file open, saving patients now...\n";
                cout << "----------------------------------------\n";
                for (int i = 0; i < PatientsInSystem.size(); i++) {
                    Patient * p;
                    p = PatientsInSystem.at(i);
                    outFile.write(reinterpret_cast<char *> (&p), sizeof(p));
                }
            }

            outFile.close();

[This next section of code is the same as above only edited after the first amount of help received]

Here is the edited version of the code... PatientList is my temporary vector which must be emptied for PatientsInSystem vector to write to the file

case 'q': {

        if (!PatientList.empty()) {
            cout << "Error. There are still patients checked in. They must be checked out before quitting." << endl;
            cout << "Printing remaining patients in the system... " << endl;
            for (int i = 0; i < PatientList.size(); i++) {
                cout << "Patient's ID: " << PatientList.at(i)->getID() << endl;
                cout << "Patient's Name: " << PatientList.at(i)->getFirstName() << " " << PatientList.at(i)->getLastName() << endl;
                cout << "Patient's Birthday: " << PatientList.at(i)->getBirthDate() << endl;
                cout << "Patient's Primary Doctor's ID: " << PatientList.at(i)->getPrimaryDoctorID() << endl;
            }
        }
        else {
            outFile.open("CurrentPatients.dat", ios::out | ios::binary);
            if (!outFile.is_open()) {
                cout << "File not open." << endl;
            }
            else {
                cout << "Binary file open, saving patients now...\n";
                cout << "----------------------------------------\n";
                for (int i = 0; i < PatientsInSystem.size(); i++) {
                    outFile.write(reinterpret_cast<char *> (PatientsInSystem.at(i)), sizeof(Patient));
                }
            }

            outFile.close();

Answer 1

Is there a reason you are using an array of pointers vs a flat array of structs?

You are writing the local pointer variable p , instead of the Patient data. You would just pass p instead of &p (or just pass .at() directly), and the bytes parameter should be sizeof(Patient) .

If these are pointers to different sized derived classes, this has issues.

Also, the loop won't every be entered, because its in the block entered when .empty() is true.