writing structure to a text file in c++ - c++

Question

struct student{
char name[20];
char course[20];
int age;
float gpa;
};
using namespace std;
main()
{
ifstream infile;
infile.open("student data.txt");
ofstream outfile;
outfile.open("student data 2.txt");
if(!infile || !outfile)
{
cout << "error opening or creating file" << endl;
exit(1);
}
student stu[2];
infile.seekg(0, ios::beg);
while(!infile.eof())
{
int i;
for(i=0; i<=2; i++)
{
infile >> stu[i].name;
infile >> stu[i].course;
infile >> stu[i].age;
infile >> stu[i].gpa;
}
}
outfile.seekp(0, ios::beg);
int i =0;
while(i<3)
{
outfile << stu[i].name << endl;
outfile << stu[i].course << endl;
outfile << stu[i].age << endl;
outfile << stu[i].gpa << endl;
i++;
}
infile.close();
outfile.close();
}
I am trying to figure out why this code is not working... its not giving any compilation error but when i run the application it stops working.it says rough.exe (app name) is not working. can anyone help :(

Answer 1

Alright, so this is fortunately a very simple solution! The problem you are facing is related to memory management. This line is causing you all the trouble:
student stu[2];
AND
int i =0;
while(i<3)
Basically, you're initializing 2 structs (indexes 0-1) of type student, then expecting to iterate over 3 structs (from index 0-2). When attempting to read in the third struct, you can get a memory access violation error.
So I ran your code with this text in "student data.txt"
nasir CS201 23 3
Jamil CS201 31 4
Faisal CS201 25 3.5
When only two structs were initialized, "student data 2" remained blank. However, when increasing the value to student stu[3];, "student data 2.txt" gave the following output:
nasir
CS201
23
3
Jamil
CS201
31
4
Faisal
CS201
25
3.5
Here is the code I used to create a successful version of your program, with a couple of extra printf's for debugging purposes.
#include <iostream>
#include <fstream>
struct student {
char name[20];
char course[20];
int age;
float gpa;
};
using namespace std;
int main()
{
ifstream infile;
infile.open("student data.txt");
ofstream outfile;
outfile.open("student data 2.txt");
if (!infile || !outfile)
{
cout << "error opening or creating file" << endl;
exit(1);
}
student stu[3]; //NOTE THIS LINE NOW HAS 3 STRUCTS INITIALIZED
infile.seekg(0, ios::beg);
while (!infile.eof())
{
int i;
for (i = 0; i <= 2; i++)
{
infile >> stu[i].name;
infile >> stu[i].course;
infile >> stu[i].age;
infile >> stu[i].gpa;
printf("%s %s %d %f\n", stu[i].name, stu[i].course, stu[i].age, stu[i].gpa);
}
}
outfile.seekp(0, ios::beg);
int i = 0;
while (i<3)
{
outfile << stu[i].name << endl;
outfile << stu[i].course << endl;
outfile << stu[i].age << endl;
outfile << stu[i].gpa << endl;
printf("%s %s %d %f\n", stu[i].name, stu[i].course, stu[i].age, stu[i].gpa);
i++;
}
infile.close();
outfile.close();
return 1;
}
Hope this helps!