CODEWITHSUNDEEP
c++
Fiphe
Fiphe

Reputation: 370

How can I read data from file to vector?

So I have this code where an object of class Group has vector with objects from class Student. I am already writing information about the students from the vector into a file but I have problem with reading this information back. How can I do that?

Here is my code so far: 

class Group
{
private:
string name;
vector <Student*> studentList;

public:
~Group();
Group(void);
Group(string s);
void addStudent(string name,int age,int stNum);
void removeStudent(int stNum);

friend ostream& operator << (std::ostream& out, const Group& g) {
    out << g.name << "\n";
    out << g.studentList.size() << "\n";

        for (unsigned i=0;i<g.studentList.size();i++) {
            out<< g.studentList[i]->getStudentName()<<"\n";
            out<< g.studentList[i]->getStudentAge()<<"\n";
            out<< g.studentList[i]->getStudentNumber()<<"\n"<<endl;
                }
    return out;
    }

friend istream& operator>>(std::istream& in,  Group& g){
    in >> g.name;
        for (unsigned i=0;i<g.studentList.size();i++) {
            //READ DATA FROM FILE
                }
    return in;
            }


};

Upvotes: 0

Views: 148

Answers (1)

user4581301
user4581301

Reputation: 33932

Gathering up the commentary. Note this pushes the hard part, the reading and writing, into Student and I left that bit blank. Normally I'd do it because I'm evil, but apparently in this case it is already written.

Major changes:

  • No Student pointers. Lest memory management overhead and better cache friendliness! By Grabthar's hammer. What a savings.
  • Student does the Student reading and writing.
  • std::vector handles the element counting so it doesn't need to be stored in and read from the output. Note: This could slow the reading down a little because you can't pre-allocate storage in the vector.
#include <string>
#include <iostream>
#include <vector>

// note the lack of using namespace std;
// it can be problematic, and especially so in a header.

class Student
{
    //fill in the blanks
    friend std::ostream& operator <<(std::ostream& out, const Student& s)
    {
        //fill in the blanks
        return out;
    }

    friend std::istream& operator >>(std::istream& in, const Student& s)
    {
        //fill in the blanks
        return in;
    }
};

class Group
{
private:
    std::string name;
    std::vector<Student> studentList; // death to pointers!

public:
    //~Group(); // Don't need a destructor without the pointer
    Group(void); 
    Group(std::string s);
    void addStudent(std::string name, int age, int stNum);
    void removeStudent(int stNum);
    friend std::ostream& operator <<(std::ostream& out, const Group& g)
    {
        out << g.name << "\n";
        //out << g.studentList.size() << "\n"; not necessary. vector handles it.
        for (std::vector<Student>::const_iterator it = g.studentList.cbegin();
             it != g.studentList.cend();
             ++it)
        {
            if (!(out << *it))// let Student's << do all the work
            { // write failed. Might as well stop trying to write.
                break;
            }
        }
        return out;
    }

    friend std::istream& operator>>(std::istream& in, Group& g)
    {
        in >> g.name;
        Student temp;
        while (in >> temp) // let Student's >> do all the work
        {
            g.studentList.push_back(temp);
        }
        return in;
    }
};

Upvotes: 1

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