writing inputs to file and reading from file in C++ - c++

Question

I was able to finally produce a working code on inputting and displaying n student details (Student ID#, Name and Age)... although the name is not full name capable, I would like to write these inputs to a text file and then read from text file also. I will appreciate any help, please:
#include <stdio.h>
#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <fstream>
using namespace std;
struct student
{
int sno, sage;
char sname[100];
};
int main(int e, char* argv[])
{
struct student s[e];
int i;
ofstream outfile;
outfile.open("info.txt");
printf("How many entries are you making?: ");
scanf("%d",&e);
printf(" \n");
printf("Please enter Student Information:\n");
for(i=0;i<e;++i)
{
s[i].sno=i+1;
printf("\nEnter Information for student %d\n",s[i]);
printf("================================\n");
cout<<"\nEnter (4 digits) student ID No: ";
cin>>s[i].sno;
cout<<"\nEnter student's name: ";
cin>>s[i].sname;
cout<<"\nAge of student: ";
cin>>s[i].sage;
printf("\n");
//If i do this, I get only first set of data
outfile <<s[i].sno<<" "<<s[i].sname<<" "<<s[i].sage<<endl;
/*I am trying to get data into txt file using the loop below but it looks odd and it collects some of the first set of data, and completes it like this: 1212 kop 23
1627953384 1629646589*/
/*for(i=0;i<e;++i)
{
outfile <<s[i].sno<<" "<<s[i].sname<<" "<<s[i].sage<<endl;
}*/
outfile.close();
}
printf("Displaying information of student(s):\n");
printf("==================================\n");
for(i=0;i<e;++i)
{
printf("\nInformation for Student %d:\n",i+1);
cout<<"\nStudent ID:"<<s[i].sno;
cout<<"\nStudent name: "<<s[i].sname;
cout<<"\nAge of student: "<<s[i].sage;
printf("\n\n");
}
return 0;
}

Answer 1

I suggest starting with a simple program that writes to a file:
#include <fstream>
#include <iostream>
#include <cstdlib>
int main(void)
{
std::ofstream output_file("text.txt");
std::cout << "Writing to output file.\n";
output_file << "This is my text.\n";
output_file.flush();
std::cout << "Finished writing to file.\n";
output_file.close();
std::cout << "Paused. Press Enter to continue.\n";
std::cin.ignore(100000, '\n');
return EXIT_SUCCESS;
}
After executing the above program, you should verify that the text file contains the correct text.
Next, you can add other code, such as prompting the User and obtaining the input.

Answer 2

I think you don't know how to read or write through file. That's why you are having problem. There are two ways which people generally use. Go through these two sample tutorial for good understanding of these methods.
- c methods
- c++ methods
This is your code which I've modified to read and write from files using both methods -
Given Input file - student.txt. //first line No. of input
2
1234 manish 34
4321 mukesh 43
Code
#include <iostream>
#include <cstdio>
#include <fstream>
using namespace std;
struct student
{
int sno, sage;
char sname[50];
};
//Read data using C Method
void ReadAndWriteCMethod(){
student s[100];
FILE* f;
f = fopen("student.txt","r");
int N;
fscanf(f,"%d",&N);
**//Reading from file**
for(int i=0; i<N; i++){
fscanf(f,"%d %s %d",&s[i].sno, &s[i].sname, &s[i].sage);
}
fclose(f);
**//Writing over file**
f = fopen("wstudent1.txt","w+");
for(int i=0; i<N; i++){
cout<<s[i].sno<<" "<<s[i].sname<<" "<<s[i].sage<<endl;
fprintf(f,"%d %s %d\n",s[i].sno,s[i].sname,s[i].sage);
}
fclose(f);
}
//Reading and writing using C++
void ReadAndWriteCPlusPlusMethod(){
student s[100];
**// Reading data**
std::ifstream fin("student.txt");
char s2[100];
int N; fin>>N;
for(int i=0; i<N; i++){
fin>>s[i].sno>>s[i].sname>>s[i].sage;
cout<<s[i].sno<<" "<<s[i].sname<<" "<<s[i].sage<<endl;
}
fin.close();
**//Writing data**
std::ofstream fout("wstudent2.txt");
for(int i=0; i<N; i++){
fout<<s[i].sno<<" "<<s[i].sname<<" "<<s[i].sage<<endl;
}
fout.close();
}
int main()
{
ReadAndWriteCMethod();
ReadAndWriteCPlusPlusMethod();
}
After running, this will generate two files wstudent1.txt and wstudent2.txt files.