How can i save vectors of type class in file and read it
Dec 30, 2016 at 12:20am Dec 30, 2016 at 12:20am UTC
I am currently using below program to write one object of class student inside a file and than read it but as i try to save more than one object than read it the output is not correct:
To read an object:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
#include <fstream>
#include <string.h>
#include <iostream>
#include <vector>
using namespace std;
class Student {
public : int a,b;
};
int main() {
vector<Student> one;
Student s;
s.a=2; s.b=3;
one.push_back(s);
s.a=23; s.b=11;
one.push_back(s);
ofstream ofs("fifthgrade.ros" , ios::binary);
ofs.write((char *)&s, sizeof (s));
for (int i=0;i<one.size();i++) {
cout<<one[i].a<<"\t" <<one[i].b<<endl;
}
return 0;
}
Here i have created two vectors which contains two objects. Any other way in which i can save more than one object inside a file is ok for me. To read a file :
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
#include <fstream>
#include <string.h>
#include <iostream>
#include <vector>
using namespace std;
class Student {
public : int a,b;
};
int main() {
vector<Student> two(1);
ifstream ifs("fifthgrade.ros" , ios::binary);
ifs.read((char *)&two, sizeof (two));
cout<<two[0].a<<endl;
return 0;
}
I get segmentation fault when i do this. Is their any way in which i can save group of objects either of class or struct inside a file and than again read it like above.
Last edited on Dec 30, 2016 at 12:20am Dec 30, 2016 at 12:20am UTC
Dec 30, 2016 at 12:44am Dec 30, 2016 at 12:44am UTC
misread post.
Last edited on Dec 30, 2016 at 12:57am Dec 30, 2016 at 12:57am UTC
Dec 30, 2016 at 12:54am Dec 30, 2016 at 12:54am UTC
Maybe like this - store the size, and then the data. In a vector, the elements are stored in consecutive memory locations so this should be ok. There might be safer ways to approach this.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59
#include <fstream>
#include <iostream>
#include <vector>
using namespace std;
class Student {
public :
int a;
int b;
};
void create_file()
{
vector<Student> one;
Student s;
s.a=2; s.b=3;
one.push_back(s);
s.a=23; s.b=11;
one.push_back(s);
ofstream ofs("fifthgrade.ros" , ios::binary);
unsigned size = one.size();
ofs.write( reinterpret_cast <char *>(&size), sizeof (size));
ofs.write( reinterpret_cast <char *>(one.data()), sizeof (Student) * size );
std::cout << "\nTo file\n" ;
for (size_t i=0; i<one.size(); i++)
{
cout << one[i].a << "\t" << one[i].b << '\n' ;
}
}
void read_file()
{
ifstream ifs("fifthgrade.ros" , ios::binary);
unsigned size;
ifs.read( reinterpret_cast <char *>(&size), sizeof (size));
vector<Student> two(size);
ifs.read( reinterpret_cast <char *>(two.data()), sizeof (Student) * size );
std::cout << "\nFrom file\n" ;
for (size_t i=0; i<two.size(); i++)
{
cout << two[i].a << "\t" << two[i].b << '\n' ;
}
}
int main()
{
create_file();
read_file();
}
Topic archived. No new replies allowed.