Why input stream object fails after reading file to the end?

Question

Here is the code . It is giving the EXACT output as shown below means it is reading the file. But it is also showing fails as you can see it means fin.fails() is true. I want to know why this is true although i am successful in reading the file.

#include<fstream>
#include<iostream>
using namespace std;
int main()
{   ifstream fin;
    fin.open("pro.txt");
    char ch;
    int data;
    while(!fin.eof())//!(fin >> ch).eof()
    {
        fin.get(ch);
        cout<<ch;
        if(fin.fail()) {
            cout<<"fails";
        break;
        }
    }
    fin.clear();
    fin.seekg(0);
    int pos=(int)fin.tellg();
    cout<<"\n this is :"<<pos;
    fin.close();
    return 0;
}

Output is :
this is my name
fails
this is 0

Contents of pro.txt:
this is my name

Don't know why this is happening!

[OT] Do not use `eof` for a loop condition: http://stackoverflow.com/questions/5605125/why-is-iostreameof-inside-a-loop-condition-considered-wrong — NathanOliver, Oct 03 '16 at 18:02
Try `while (fin >> ch)`, but as it doesn't output anything, it's probable that your opening fails (for example if the current working directory is not the one you expect). — Christophe, Oct 03 '16 at 18:04
this is a complete different question from the above mentioned — akitsme, Oct 03 '16 at 18:07
@AkashKabir Duplicates aren't about questions, but the answers that can be found there. If you don't think that answers your question, edit it and explain exactly why not. — πάντα ῥεῖ, Oct 03 '16 at 18:11
Where did you read to use `while(!fin.eof())`? We need to correct that book. — Lightness Races in Orbit, Oct 03 '16 at 18:13
I am just saying this because i can't relate my answer to the answer given in that question . It will nice if you answer my question with reference to that question — akitsme, Oct 03 '16 at 18:15
@LightnessRacesinOrbit it is working correctly!! better u can use it tooo but i just wanted to ask why the fin.fails() is true. — akitsme, Oct 03 '16 at 18:17
@Christophe `while(fin>>ch)` working but it is skipping one letter each time i.e this is my name output: hssyae WHY? — akitsme, Oct 03 '16 at 18:20
@πάνταῥεῖ sorry but now i read it and my file `pro.txt` is in same working directory — akitsme, Oct 03 '16 at 18:22
output is showing ! this means it is reading the file but also failing after reading it ... now i think my question answer is different — akitsme, Oct 03 '16 at 18:23
@AkashKabir As mentioned edit your question to provide a [MCVE], and explain any errors exactly. — πάντα ῥεῖ, Oct 03 '16 at 18:24
`fin>>ch` not showing white spaces can you provide another way of reading file with whitespaces — akitsme, Oct 03 '16 at 18:34

score 0 · Answer 1 · answered Oct 03 '16 at 18:42

0

Still can't find why the fin.fails() is true because i think no one willing to But i figured out to read white spaces and file without making fin.fails() =true . just replace the while(!fin.eof()) with while(fin.get(ch)) and remove the fin.get(ch) present in while body -> this was the reason why my output was skipping one character for each read.. this i had mentioned in the comments.

answered Oct 03 '16 at 18:42

akitsme

41
11

Yes, I mentioned this in comments too, but you told me I was wrong. :smh: – Lightness Races in Orbit Oct 03 '16 at 19:22
i didn't said that ! i know that was my fault and `fin>>ch` don't manages white spaces try it yourself – akitsme Oct 03 '16 at 19:33

Corristo · Answer 2 · 2016-10-03T20:38:52.523

The problem is the following: Reading the last character in your file with get will not set the eofbit, so the call to fin.eof() in your while condition still returns false after you read the last character of the file inside the loop body. Then during the iteration following the read of the last character you try to read another character inside the loop body, even though there is no character to read anymore. This will set the eofbit and the failbit as per specification of get.

TL;DR: Reading over the end of a file is supposed to set the failbit.

Why input stream object fails after reading file to the end?

2 Answers2