Why can't I input the integers from a file?

Question

I'm trying to get this C++ code to input a series of numbers from a text file:

    int x = 0;
    cin >> x;

    ifstream iffer;
    int numbers[12];
    iffer.open("input.txt");
    for (int i = 0; i < 12; i++){
        iffer >> numbers[i];
    }

This doesn't seem to work on the Mac. Every cell will equal to 0 regardless of the values in the text file. In other words, the ifstream isn't assigning the numbers.

How can I make this work? Is it a Mac issue and if so, how can I get it to work?

Thanks!

Anthony Glyadchenko

Answer 1

Tried (VC9.0):

#include <iostream>
#include <fstream>

int main()
{
    using namespace std;

    int x = 0;
    cin >> x;

    ifstream iffer;
    int numbers[12];
    iffer.open("input.txt");
    for (int i = 0; i < 12; i++){
        iffer >> numbers[i];
    }
    for (int i = 1; i < 12; i++){
        numbers[i] = i;
    }

    return 0;
}

That worked, but the second loop is wrong.

Answer 2

Maybe opening the file failed?
You can check if the failbit of iffer is set with fail()

if(iffer.fail())
{
  cout << "Failed to open file." << endl;
}

Answer 3

It should work, but be aware, that "get" will always just read one character. This is what I tested, also on Mac OSX, but this has nothing to do with your OS, since it is standard C++:

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

int main(){
    ifstream iffer;
    iffer.open("input.txt");
    char numbers[12];
    int i = 0;
    while (iffer.good()){
        numbers[i] =  iffer.get();
        i++;
    }
    for (int n = 0; n < 8; n++){
        cout << numbers[n];
    }        
    cout << endl;
    iffer.close();
}

The file "input.txt" I am reading in. Make sure this file is in your working directory!:

12345678

While reading the file every character will be stored in your array. So when you have a file like

1 2 3 4 5 6 

your array will contain

numbers[0] = '1'
numbers[1] = ' ' 
numbers[2] = '2'
numbers[3] = ' '
...

Answer 4

This sounds like a path issue. You have an "input.txt" file somewhere, but not in the current directory. If this is in a GUI application, keep in mind that the current directory is somewhat unpredictable and you should either give an absolute path or a path relative to some known path (e.g. the path to the current application CFBundle).

Just to test, I just created a Unix program including your precise code wrapped in the following code:

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

int main() {
    int x = 0;
    // your code
    cout << numbers[5] << endl;
    return 0;
}

It worked, so if this is in a command-line program and you launched it from the right directory, you must be changing the current directory somewhere in your app.