eof (end of file) function inside while loop in C++

Asked Sep 22 '14 at 20:14

Active Sep 22 '14 at 20:14

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I'm reading a book "Guide to Scientific Computing in C++" and there is a code inside the book that doesn't run as supposed to do.

Here is the listing from the book as follows:

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

int main()
{
int x[6], y[6];
ifstream read_file("Output.dat");
assert(read_file.is_open());

int i = 0;
while (!read_file.eof())
{

    read_file >> x[i] >> y[i];
    cout <<x[i]<<" "<< y[i]<<"\n";
    i++;

}
read_file.close();
return 0;
}

Here is my "output.dat":

When I run the program, I get :

0 0
1 0
0 1
0 0
1 0
0 1
4195984 807

So I wonder why it outputs the trash data in the last line which is not in my data file.

asked Sep 22 '14 at 20:14

ofenerci

http://stackoverflow.com/questions/5605125/why-is-iostreameof-inside-a-loop-condition-considered-wrong – WhozCraig Sep 22 '14 at 20:16
@WhozCraig Just was about doing the same, you were quicker ;) ... – πάντα ῥεῖ Sep 22 '14 at 20:18
The state of scientific computing in C++ apparently leaves a lot to be desired. – n. 'pronouns' m. Sep 22 '14 at 20:28
I have read the answer but still confused! – ofenerci Sep 22 '14 at 20:42
It is possible that the `eof` flag will not be seat until ***after*** you try to read from the stream. That means that inside the while loop the program is using bad data at the end when the `eof` was not set until ***after*** it did the `>>`. – Galik Sep 22 '14 at 21:28
And that's not the only problem with this code. The read could fail for other reasons that go unchecked. – Galik Sep 22 '14 at 21:39

eof (end of file) function inside while loop in C++

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