Eof causes loop

MarlonDean · 08-06-2009, 01:37 PM

Hi People,

Its been awhile since I worked on C++, but I am back on the horse again.

My problem seems to be that EOF causes a loop.

Example :

I have a file with 3 lines of data, 50 characters, a space,4 numbers, a space, x amount of characters.

The first 50 characters is a sort of a multiple choice answers that are compared to 50 characters in another file. The 4 numbers is a students ID, and the last bunch of characters is the students ID.

Now you should ouput the data to a file like so:

Student_number Student_Name Mark_obtained

First I tried this...

Code:

#include <iostream>
#include <fstream>
#include <cstdlib>
#include <vector>
using namespace std;

void WriteReport(ifstream& booklet_file,ifstream& answer_file)
{

char character_answer,character_booklet,next;
int count=0,;





while(!answer_file.eof())
{    
    while(next!=' ')
   {
    booklet_file.get(character_booklet);
    if (character_booklet==next)
    count++;
    answer_file.get(next);
   }  
  
   answer_file.get(next);
  
   while(next!=' ')
    {
     cout<<next;
     answer_file.get(next);
    }  
  cout<<" ";
  answer_file.get(next);
  
  while(next!='\n')
  {
   cout<<next;
   answer_file.get(next);
  } 

cout<<" ";
cout<<count;
cout<<endl;

} 
}
int main()
{
   
   ifstream booklet_file,answer_file;
   ofstream report_file;

   
   booklet_file.open("booklet.dat");
   answer_file.open("answer.dat");
   
   if (booklet_file.fail())
    {
     cout<<"File read error."<<endl;
     exit(1);
    }  
   
   if (answer_file.fail())
    {
      cout<<"File read error."<<endl;
      exit(1);
    }
    

  WriteReport(booklet_file,answer_file);
booklet_file.close();
answer_file.close();
report_file.close();
    return 0;
}

But this causes a ugly loop where only the last character is displayed over & over again.

Then I tried

Code:

#include <iostream>
#include <fstream>
#include <cstdlib>
#include <vector>
using namespace std;

void WriteReport(ifstream& booklet_file,ifstream& answer_file)
{

char character_answer,character_booklet,next;
int count=0,;





while(answer_file>>next)
{    
    while(next!=' ')
   {
    booklet_file.get(character_booklet);
    if (character_booklet==next)
    count++;
    answer_file.get(next);
   }  
  
   answer_file.get(next);
  
   while(next!=' ')
    {
     cout<<next;
     answer_file.get(next);
    }  
  cout<<" ";
  answer_file.get(next);
  
  while(next!='\n')
  {
   cout<<next;
   answer_file.get(next);
  } 

cout<<" ";
cout<<count;
cout<<endl;

} 
}
int main()
{
   
   ifstream booklet_file,answer_file;
   ofstream report_file;

   
   booklet_file.open("booklet.dat");
   answer_file.open("answer.dat");
   
   if (booklet_file.fail())
    {
     cout<<"File read error."<<endl;
     exit(1);
    }  
   
   if (answer_file.fail())
    {
      cout<<"File read error."<<endl;
      exit(1);
    }
    

  WriteReport(booklet_file,answer_file);
booklet_file.close();
answer_file.close();
report_file.close();
    return 0;
}

And again a ugly screen full of characters.

when I change the function to this

Code:

#include <iostream>
#include <fstream>
#include <cstdlib>
#include <vector>
using namespace std;

void WriteReport(ifstream& booklet_file,ifstream& answer_file)
{

char character_answer,character_booklet,next;
int count=0,;

    while(next!=' ')
   {
    booklet_file.get(character_booklet);
    if (character_booklet==next)
    count++;
    answer_file.get(next);
   }  
  
   answer_file.get(next);
  
   while(next!=' ')
    {
     cout<<next;
     answer_file.get(next);
    }  
  cout<<" ";
  answer_file.get(next);
  
  while(next!='\n')
  {
   cout<<next;
   answer_file.get(next);
  } 

cout<<" ";
cout<<count;
cout<<endl;

} 

int main()
{
   
   ifstream booklet_file,answer_file;
   ofstream report_file;

   
   booklet_file.open("booklet.dat");
   answer_file.open("answer.dat");
   
   if (booklet_file.fail())
    {
     cout<<"File read error."<<endl;
     exit(1);
    }  
   
   if (answer_file.fail())
    {
      cout<<"File read error."<<endl;
      exit(1);
    }
    

  WriteReport(booklet_file,answer_file);
booklet_file.close();
answer_file.close();
report_file.close();
    return 0;
}

The output is much better, but it prints only 1 record, ignoring the remainder of the file.

I have been through chapter 6 of "Problem Solving with C++" by Savitch and I cant find the reason why EOF causes the loop.

I haven't been a active programmer for about 6 months now, so please be gentle.

PS This is a homework assignment, so if you can, I would appreciate tips (not full code)

Thanks!

msh · 08-07-2009, 02:11 AM

In future:

Current version of code only - despite the popular opinion, programmers don't like to read the code of others unless it's really interesting (yours is not).
Your indentation is a mess - fix it.
Spaces around operators, and after commas.

You say we have a files with three lines of data. That would imply a format like this:

Code:

aaaaabbbbbcccccdddddeeeeeaaaaabbbbbcccccdddddeeeee // test answers
1234 // student ID
Johnny B. Goode //student name

However, you say you have space between the "lines" which makes me guess, and this is supported by your code, that you have a list of space separated values, e.g.:

Code:

aaaaabbbbbcccccdddddeeeeeaaaaabbbbbcccccdddddeeeee 1234 Johnny B. Goode

WriteReport() is a mess.

Variable next is not initialized before use. You're approach to reading the test answers string is debatable - it would be easier to read it in whole (into an array) and when do counting and comparison. E.g.:

Code:

char answers[51];
// Read all until we hit the first space or 50 characters are read,
// see http://www.cplusplus.com/reference/iostream/istream/getline/
booklet_file.getline(answers, 51, ' ');

Same for the other elements - student ID and student name. Especially for the name.

This should get you started.

Elysia · 08-07-2009, 03:39 AM

Don't use eof for loop conditions either - see FAQ.

08-07-2009, 02:11 AM	#2
msh Novice Join Date: Jul 2009 Posts: 32	In future: Current version of code only - despite the popular opinion, programmers don't like to read the code of others unless it's really interesting (yours is not). Your indentation is a mess - fix it. Spaces around operators, and after commas. You say we have a files with three lines of data. That would imply a format like this: Code: aaaaabbbbbcccccdddddeeeeeaaaaabbbbbcccccdddddeeeee // test answers 1234 // student ID Johnny B. Goode //student name However, you say you have space between the "lines" which makes me guess, and this is supported by your code, that you have a list of space separated values, e.g.: Code: aaaaabbbbbcccccdddddeeeeeaaaaabbbbbcccccdddddeeeee 1234 Johnny B. Goode WriteReport() is a mess. Variable next is not initialized before use. You're approach to reading the test answers string is debatable - it would be easier to read it in whole (into an array) and when do counting and comparison. E.g.: Code: char answers[51]; // Read all until we hit the first space or 50 characters are read, // see http://www.cplusplus.com/reference/iostream/istream/getline/ booklet_file.getline(answers, 51, ' '); Same for the other elements - student ID and student name. Especially for the name. This should get you started.
msh is offline

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