Question

目前我遇到一个大问题，我需要将数据填充到MAP并将其写入文件。

该文件将如下所示：

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

这是代码

  //  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();


}

此代码的问题在于我必须添加 studentNo 和性别作为函数的参数，然后才会覆盖该文件，但我真正想要的是是输入一个名字，然后修改每个主题分数。

示例我真正想要的。

在进行任何修改之前

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

提示符

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

修改后

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

正如您所见， studentNo 和性别仍然存在，我无需输入值。唯一改变的是主题分数。我该如何完成这个输出？目前我的代码总是需要输入 studentNo 和性别的输入。

Answer 1

根据名称，您可以获得该学生的迭代器，然后获取原始数据

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

假设您要更新名为＆＃39; Dragon＆＃39;的学生记录的StudentNo。你可以这样做：

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;

如何不覆盖MAP c ++中的现有数据？

2 个答案: