保存并加载c ++程序

Question

Ok so I figured out and learned a lot of stuff today and I want to thank the community for that. I haven't had any bump in the roads for a few hours now but now I'm stuck.

The last bump in the road. Saving and Loading my program. I have no idea where to start. I looked at how fwrite... and fread... works and all the examples are for programs that aren't split. I don't know where to start with my files. I'll put up 2 functions. If someone can help me how to do save those I can probably figure out the rest.

in gradebook.h

class Student {
 public: 
  string last;
  string first;
  int student_id;
};

class Course {
 public:
  string name;
  int course_id;
  vector <Student> students;
};

class Gradebook {
 public:
  Gradebook();
  void addCourse();
  void addStudent();
 private:
  vector <Course> courses;
};

in gradebook.cpp

void Gradebook::addCourse() {

 int i, loop=0;

    cout << "Enter Number of Courses: ";
cin >> loop;

for(i=0; i<loop; i++) {

    //create newEntry to store variables
    Course newEntry;

    cout << "Enter Course ID: ";
    cin >> newEntry.course_id;

    cout << "Enter Course Name: ";
    cin >> newEntry.name;

    //set variables from newEntry in Courses
    courses.push_back(newEntry);

}

}
void Gradebook::addStudent() {

    int i, loop=0;

cout << "Enter Number of Students: ";
cin >> loop;

for(i=0; i<loop; i++) {

    //create newEntry to store variables
    Student newEntry; 

    cout << "Enter Student ID: ";
    cin >> newEntry.student_id;

    cout << "Enter Last Name: ";
    cin >> newEntry.last;

    cout << "Enter First Name: ";
    cin >> newEntry.first;

    //set variables from newEntry in Students
    courses[0].students.push_back(newEntry);

}
}

So if a user was to input some variables in courses and students how would i use fwrite... to save the data?

Answer 1

I wouldn't recommend fwrite , instead look into <fstream> . ifstream , ofstream

Basic saving:

ofstream out("data.txt"); //save file data.txt
out << thedata; //use the << operator to write data

Basic loading:

ifstream in("data.txt"); //reopen the same file
in >> thedata; //use the >> operator to read data.

Answer 2

Here's some sample code that might help without solving the whole thing for you.

#include<iostream>
#include<string>
#include<vector>
#include<fstream>

class Student {
public: 
    Student()
    : student_id(0)
    {
    }
    Student(const std::string &f, const std::string &l, int id)
        : first(f)
        , last(l)
        , student_id(id)
    {
    }
    std::string last;
    std::string first;
    int student_id;
};

std::ostream &operator <<(std::ostream &os, const Student &s)
{
    os << s.last << '\t' 
       << s.first << '\t' 
       << s.student_id << '\t';
    return os;
}

std::istream &operator >>(std::istream &is, Student &s) 
{
    is >> s.last
       >> s.first
       >> s.student_id;
    return is;
}


bool WriteIt(const std::string &sFileName)
{
    std::vector<Student> v;
    v.push_back(Student("Andrew", "Bogut",   1231));
    v.push_back(Student("Luc",    "Longley", 1232));
    v.push_back(Student("Andrew", "Gaze",    1233));
    v.push_back(Student("Shane",  "Heal",    1234));
    v.push_back(Student("Chris",  "Anstey",  1235));
    v.push_back(Student("Mark",   "Bradtke", 1236));

    std::ofstream os(sFileName);
    os << v.size();
    for (auto s : v)
        os << s;

    return os.good();
}

bool ReadIt(const std::string &sFileName)
{
    std::ifstream is(sFileName);
    int nCount(0);

    is >> nCount;
    if (is.good())
    {
        std::vector<Student> v(nCount);
        for (int i = 0; i < nCount && is.good(); ++i)
            is >> v[i];
        if (is.good())
            for (auto s : v)
                std::cout << s << std::endl;
    }

    return is.good();
}

int main()
{
    const std::string sFileName("Test.dat");
    return !(WriteIt(sFileName) && ReadIt(sFileName));
}

Bonus points if you recognise who my "students" are. :-)