Alex Rivera | Logout

Reading from text file until EOF repeats last line

Asked 2008-08-22T02:21:07.440
133

The following C++ code uses a ifstream object to read integers from a text file (which has one number per line) until it hits EOF. Why does it read the integer on the last line twice? How to fix this?

Code:

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

int main()
{
    ifstream iFile("input.txt");    // input.txt has integers, one per line

    while (!iFile.eof())
    {
        int x;
        iFile >> x;
        cerr << x << endl;
    }

    return 0;
}

input.txt:

10  
20  
30

Output:

10  
20  
30  
30

Note: I've skipped all error checking code to keep the code snippet small. The above behaviour is seen on Windows (Visual C++), cygwin (gcc) and Linux (gcc).

c++ iostream fstream
Edit
Report

2 Answers

45

I like this example, which for now, leaves out the check which you could add inside the while block:

ifstream iFile("input.txt");        // input.txt has integers, one per line
int x;

while (iFile >> x) 
{
    cerr << x << endl;
}

Not sure how safe it is...

answered 2008-08-22T02:59:25.477
2
int x;
ifile >> x

while (!iFile.eof())
{  
    cerr << x << endl;        
    iFile >> x;      
}
answered 2013-04-11T20:29:34.080

Your Answer