如何不覆蓋MAP C++中的現有數據？

Question

目前我正面臨一個大問題，我需要將數據填充到MAP並將其寫入文件。

該文件將是這個樣子：

Name StudentNo Gender Indian English Math History Moral Average 
Dragon 33899  M  100  100 100 100  100  100 

下面的代碼

// Function to modify a student's exam scores. 
    void Student::modifyScore(string newName, int newStudentNo, char newGender, int newIndian, int newEnglish, int newMath, int newHistory, int newMoral) { 


    map<string, tuple<int, char,int, int, int, int, int> > data; 

    // Read file and fill data map 
    ifstream studentRec("StudentRecord.txt"); 
    string line; 

    while (getline(studentRec, line)) 
    { 
     string name; 
     int studentNo; 
     char gender; 
     int indian, english, math, history, moral; 
     stringstream ss(line); 
     ss >> studentNo>>gender>>name >> indian >> english >> math >> history >> moral; 
     data[name] = make_tuple(studentNo, gender,indian, english, math, history, moral); 

    } 

    studentRec.close(); 
    auto it = data.find(newName) ; 
    if (it == data.end()) // student not in map, that's an error 
     return ; 
    // now it->second holds your student data, 
    int studentNo = get<0>(data-second) ; 
    char gender = get<1>(data->second) ; 
    // Modify data 
    data[newName] = make_tuple(newStudentNo, newGender ,newIndian,newEnglish, newMath, newHistory, newMoral); 
    // Open same file for output, overwrite existing data 
    ofstream ofs("StudentRecord.txt"); 

    for (auto entry = data.begin(); entry != data.end(); ++entry) 
    { 
     tie(newStudentNo, newGender,newIndian,newEnglish, newMath, newHistory, newMoral) = entry->second; 
     int average = averageScore(newIndian,newEnglish, newMath, newHistory, newMoral); 

     ofs << left << setw(15) << entry->first << setw(15) <<newGender<<newName<< newIndian << setprecision(2) << newEnglish << setw(15) << right << newMath << setw(15) << newHistory << setw(15) << newMoral << average << endl; 
    } 
    ofs.close(); 


} 

這段代碼的問題是，我要補充studentNo和性別作爲參數的功能，那麼只有它會覆蓋文件，但我真正想要的只是輸入一個名稱，然後修改每個主題的分數。

示例我真正想要的。

任何修改之前

Name StudentNo Gender Indian English Math History Moral Average 
    Dragon 33899  M  100  100 100 100  100  100 

提詞

Enter the name of the student: // It will find the map that has name Dragon 
    --> Dragon 

Enter the new score for indian subject 
    --> 77 

Enter the new score for English subject 
    --> 55 

Enter the new score for Math subject 
    --> 100 

Enter the new score for History subject 
    --> 89 

Enter the new score for Moral subject 
    --> 62 

修改後

 Name StudentNo Gender Indian English Math History Moral Average 
    Dragon 33899  M  77  55 100 89  62  76.6 

正如你所看到的學生沒有和性別仍然存在，沒有我需要輸入的值。唯一改變的是主題分數。我將如何完成這個輸出？目前我的代碼將始終需要我輸入studentNo和性別以及輸入。

Answer 1

給定的名稱，你可以得到一個迭代器是學生，然後得到的原始數據

auto it = data.find(name) ; // gets current student record from the map 
if (it == data.end()) // student not in map, that's an error 
    return ; 
// now it->second holds your student data 
// an auto here could be better, but we want to be sure of type 
studentNo = get<0>(it->second) ; 
gender = get<1>(it->second) ; 

Answer 2

假設你想更新StudentNo與名字「龍」你可以做學生記錄如下：

int NewStudentNo; 
string NewName="Dragon"; 

auto it = data.find(NewName) ; // gets current student record from the map 
if (it == data.end()) // student not in map, that's an error 
    return ; 
std::cout<<"Enter new student Number"; 
std::cin>>NewStudentNo; 
std::get<0>(it->second) = NewStudentNo;