Question

我的ReadFile函数无法读取我的整个文件。该文件包含几行信息，每行信息都与一个学生有关。

函数（或while循环）正在读取前两个记录，然后退出循环。它可以正确读取所有内容，但是为什么不继续读取整个文件（其中有13条记录）呢？

我已经尝试过while(!infile.eof())，但是该程序甚至没有与此一起运行。

这是我的ReadFile块：

void ReadFile() {// Reads data file into array

    ifstream infile;

    infile.open(cTextFileName);

    if (!infile.good()) {
        cout << "Cant find text data file!" << endl;
        exit(1);
    }

    int i = 0;
    int status;
    //bool endOfFile = infile.eof();

    infile >> gRecs[i].StudentNo;

    while (infile) {
        infile >> gRecs[i].FirstName;
        infile >> gRecs[i].LastName;
        infile >> gRecs[i].NumSubjects;
        //cout << "ENTERED WHILE LOOP" << endl;

        for (int j = 0; j < gRecs->NumSubjects; j++) {
            infile >> gRecs[i].Subjects[j].Code;
            infile >> status;

            if (status == 0) {
                gRecs[i].Subjects[j].Status == eEnrolled;
            } else if (status == 1) {
                gRecs[i].Subjects[j].Status == eProvisional;
            } else {
                gRecs[i].Subjects[j].Status == eWithdrawn;
            }


            infile >> gRecs[i].Subjects[j].Mark;

        }

        i++;
        infile >> gRecs[i].StudentNo;
    }

    gNumRecs = i;
    infile.close();
    infile.clear();

    cout << gNumRecs << " Records read!" << endl;
}

Answer 1

for (int j = 0; j < gRecs->NumSubjects; j++) {

应该是

for (int j = 0; j < gRecs[i].NumSubjects; j++) {

Answer 2

我认为，解决此问题的最佳方法是完全避免它。

我将编写一个仅读取单个记录的函数，而不是尝试读取整个文件的单个函数。然后重复调用该函数，直到读取了整个文件。为了符合标准库其余部分的工作方式，读取单个记录的函数应命名为operator>>。它应该收到对istream的引用和对记录的引用，并在完成后返回对istream的引用。

std::istream &operator>>(std::istream &is, gRec &record) {
    is >> record.FirstName;
    is >> record.LastName;
    is >> record.NumSubjects;
    for (int i=0; i<record.NumSubjects; i++) {
        is >> record.subjects[i].code;

        int raw_status;
        is >> raw_status;
        record.subject[i].status = cvt_status(raw_status);
        is >> record.mark;
    }
    return is;
}

我个人可能会从那里进行一些更改。我将创建一个Status，Subject和Schedule，它们各自定义自己的operator>>以从文件中读取自身：

class Status {
    enum class status { enrolled, provisional, withdrawn } s;

    friend std::istream &operator>>(std::istream &is, Status &s) { 
        int i;
        is >> i;
        switch (i) { 
            case 1: s.s = status::enrolled;    break;
            case 2: s.s = status::provisional; break;
            case 3: s.s = status::withdrawn;   break;
        }
        return is;
    }
};

class Subject {
    int code;
    Status status;
    int mark;
public:
    friend std::istream &operator>>(std::istream &is, Subject &s) { 
        return is >> s.code >> s.status >> s.mark;
    }
};

class Schedule {
    std::vector<Subject> classes;
public:
    friend std::istream &operator>>(std::istream &is) {
        int num;
        is >> num;
        for (int i=0; i<num; i++) {
            Subject temp;
            is >> temp;
            classes.push_back(temp);
       }
       return is;
    }
};

那么一条记录将是这样的：

class Record {
    std::string FirstName, LastName;
    Schedule classes;
public:
    std::istream &operator>>(std::istream &is, Record &r) {
        return is >> r.FirstName >> r.LastName >> r.classes;
    }
};

最后，读取充满学生记录的整个文件将是这样的：

std::ifstream infile("filename");
std::vector<Record> records{std::istream_iterator<Record>(infile), {}};

While循环无法读取整个ifstream文件

2 个答案: