When reading a text file with loop, it gives lots of white lines to console, and writes down lots of "H" to the text file

Question

I have the following C++ code:

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

void main()
{
     fstream file;

     file.open("file.txt", fstream::in | fstream::out | fstream::app);

     file << "Ivan" << "\n" << "Ivan";

     string text = "";

     while (!file.eof()) {
         text = "";
         file >> text;
         cout << text;
     }

     file.close();
}

When I'm using cout to print that text to console, this gives me lots of white lines. And when I enter the .txt file, there are lots of "H" letters except for my text. I think the problem is in the loop.

Does somebody know what the problem is?

`while (!file.eof()) {` should be avoided and may cause a bug: [https://stackoverflow.com/questions/5605125/why-is-iostreameof-inside-a-loop-condition-i-e-while-stream-eof-cons](https://stackoverflow.com/questions/5605125/why-is-iostreameof-inside-a-loop-condition-i-e-while-stream-eof-cons) — drescherjm, Dec 10 '20 at 17:20
You are writing to a file then read after the position you have written. — drescherjm, Dec 10 '20 at 17:22
There are two photos above the last sentense of the question "H letters" and "White lines" — Yutat, Dec 10 '20 at 17:41

score 1 · Answer 1 · edited Dec 10 '20 at 20:37

Remove the std::ios::app flag. Passing this flag seeks to the end of the stream, so in your case you are already at the "EOF" of the file, that is why your loop fails.

Here is info from cppreference.com:

app
seek to the end of stream before each write

Try this:

fstream file("data.txt", std::ios::in | std::ios::out);
if(!file)
    cout << "!file\n";

file << "Ivan" << "\n" << "Ivan";

string text = "";

while (file >> text)
    cout << text << ' ';

You can move back the read pointer to the beginning of the file after writing:

file << "Ivan" << "\n" << "Ivan";

file.seekg(0, std::ios::beg);

string text = "";

while (file >> text)
    cout << text << ' ';

When reading a text file with loop, it gives lots of white lines to console, and writes down lots of "H" to the text file

1 Answers1