How can I read strings from a .txt file in a loop in C++

Question

My Code:

#include <Windows.h>
#include <iostream>
#include <fstream>
#include <string>

using namespace std;

string index[8];

int main() {
    int count = 0;
    ifstream input;
    //input.open("passData.txt");
    while (true) {
        input.open("passData.txt");
        if (!input) {
            cout << "ERROR" << endl;
            system("pause");
            exit(-1);
        }
        else {
            if (input.is_open()) {
                while (!input.eof()) {
                    input >> index[count];
                    count++;
                }
            }
            for (int i = 0; i < 8; i++) {
                cout << index[i] << endl;
            }
        }
        input.close();
    }
    return 0;
}

My approach: opening the file in the beginning and then close it as soon as the lines where read. Also every line should be a single entry in the array.

However, I get an error in a file called "xutility" in an iterator. The output is the "passData.txt" file, only that its read once and then the error appears.

So, my question: how can I read every line of the file in an array entry, in a loop?

Thank you!

`input >> index[count];` reads a word (e.g. a string till a whitespace is found) and not a line. — mch, Jul 04 '18 at 12:08
`int count = 0;` should be defined inside `while(true){}` loop then press ctrl+c to exit. Do you want that infinite while loop? — Ashish Shirodkar, Jul 04 '18 at 12:24
Ok so apparently you are right. I forgot to reset the counter. Thanks a lot! — Oliver Tworkowski, Jul 04 '18 at 12:32
https://stackoverflow.com/questions/20902945/reading-a-string-from-file-c — wtom, Jul 04 '18 at 12:35

score 1 · Accepted Answer · answered Jul 04 '18 at 12:03

1

The problem I see with this code is that you don't break the endless loop, like ever. Because of that you keep on incrementing the count and it finally goes out of range for your string array called index.

answered Jul 04 '18 at 12:03

pbn

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It does have an end: while(the endoffile isnt reached){increment} So thath cant be the problem :/ – Oliver Tworkowski Jul 04 '18 at 12:28
I meant the outer loop `while (true)` – pbn Jul 04 '18 at 12:32
Ok i read your answer again and from what i understand you might be right. I found the problem. As you said: the counter needs to be reset everytime the while loop starts over so that the array index starts at 0 evertyime we loop through. – Oliver Tworkowski Jul 04 '18 at 12:35

Lion King · Answer 2 · 2018-07-04T13:12:41.073

0

Look at the following code, I think it does your mission but it's simpler:

string strBuff[8];
int count = 0;
fstream f("c:\\file.txt", ios::in);
if (!f.is_open()) {
    cout << "The file cannot be read" << endl;
    exit(-1);
}
while (getline(f, strBuff[count])) {
    count++;
}

cout << strBuff[3] << endl;

edited Jul 04 '18 at 13:12

answered Jul 04 '18 at 12:38

Lion King

32,851
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score 0 · Answer 3 · answered Jul 04 '18 at 12:39

When extracting from a stream, you should check the result, rather than testing beforehand.

You don't need to call open, the constructor that accepts a string does that. You don't need to call close, the destructor does that.

You should only output lines you have read.

Note that you should stop both if your file runs out of lines, or if you have read 8 lines

You can discard most of what you have written.

#include <iostream>
#include <fstream>
#include <string>

int main()
{
    string index[8];
    std::size_t count = 0;   
    for(std::ifstream input("passData.txt"); (count < 8) && std::getline(input, index[count]); ++count)
    { 
        // this space intentionally blank
    }
    for(std::size_t i = 0; i < count; ++i)
    {
        std::cout << index[i] << std::endl;
    }
}

How can I read strings from a .txt file in a loop in C++

3 Answers3