Question

在使用 cin 输入某些值后，我试图覆盖文件中的数据。我面临的问题是，应该修改文件的函数实际上并没有正确地执行。

在这个场景中，我使用寄存器功能

添加这些数据

代码：

// register a student to the system
void Student::registerStudent(string name, int studentNo, char gender) {
        outStream.open("StudentRecord.txt", ios_base::app);
        outStream << left << setw(15) << studentNo << setw(15) << gender << right << name << endl; 
        outStream.close();
}

我添加了3次数据，然后我

    Batman   11  M   
    BatGirl  22  F
    Joker    33  M

现在出现了问题，我试图通过添加额外的主题分数来修改蝙蝠侠行

我想要的结果：

    Batman   11  M   100  22  55 22  33
    BatGirl  22  F
    Joker    33  M

姓名后面的数字是主题分数。

但是，当我运行程序修改特定行时，我得到了这个

BatGirl        22             F              -858993460     -858993460          -858993460     -858993460     -858993460
Batman         11             M              12             86                          44             24             55
Joker          33             M              -858993460     -858993460          -858993460     -858993460     -858993460

这里是特定行修改的代码

//  Function to modify a student's exam scores.
    void Student::modifyScore(string newName, 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 >> name >> studentNo>> gender>> indian >> english >> math >> history >> moral;
       data[name] = make_tuple(studentNo, gender,indian, english, math, history, moral);

    }

    studentRec.close();
    // Modify data


    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 ;
    // now it->second holds your student data
    // an auto here could be better, but we want to be sure of type
    auto studentNo = get<0>(it->second) ;
    auto gender = get<1>(it->second) ;

     data[newName] = make_tuple(studentNo, gender, 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(studentNo, gender, newIndian,newEnglish, newMath, newHistory, newMoral) = entry->second;
        //int average = averageScore(newIndian,newEnglish, newMath, newHistory, newMoral);

        ofs << left <<  setw(15) << entry->first << setw(15) << studentNo << setw(15) << gender << setw(15) << newIndian << setw(15) << newEnglish << setw(15) << right << newMath << setw(15) << newHistory << setw(15) <<  newMoral << endl;
    }
    ofs.close();


}

为了清楚起见， modifyScore 的论据是

newName --> is to find the name in the file
newIndian --> Subject scores
newEnglish --> Subject scores
newMath --> Subject scores
newHistory --> Subject scores
newMoral --> Subject scores

请指出我犯了错误的地方。谢谢！

Answer 1

问题是

   stringstream ss(line);
   ss >> name >> studentNo>> gender>> indian >> english >> math >> history >> moral;

当您遇到Batman 11 M这样的3字行时，表达式为ss >> indian will fail and activate the failbit。这意味着印度人之后的所有变量都不会被修改。就目前而言，它们是未初始化的，它解释了你得到的价值的随机性。

现在要修复此问题，您应该检测特定行中的列数，即number of words in the string，以便您可以将未修改行的状态恢复到其先前状态。

unsigned int countWordsInString(std::string const& str);

bool fullrecord(std::string const& str)
{
   return countWordsInString(str) == 8;
}

map<string, tuple<int, char,int, int, int, int, int, bool> > data; //added bool
stringstream ss(line);
bool hasGrades = fullrecord(line);
if(hasGrades )
    ss >> name >> studentNo>> gender>> indian >> english >> math >> history >> moral;
else
    ss >> name >> studentNo>> gender;
data[name] = make_tuple(studentNo, gender,indian, english, math, history, moral, hasGrades);

现在使用布尔值来决定是否保存包含或不包含成绩的行

数据输出奇怪的数字到文件，MAP c ++

1 个答案: