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

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

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 2

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 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

I tried your code, slightly modified, on both Linux (g++ 3.4.4) and Mac (g++ 4.0.1) and it works just fine!
With respect to Chuck, if input.txt does not exist, iffer.fail() is true. Since you say that's not the case...
Another possibility is a different input.txt file than what you expected. If it had too few numbers, you'd see zeros (or other garbage values). (You could test with iffer.eof(), though that might be set (appropriately) after reading the last number if there's no trailing whitespace (like a newline). So test eof() before reading!)
Alternatively, you could have a dangling pointer elsewhere in your code trashing something inappropriately. Sometimes adding and removing large chunks of code will permit you to manually "binary search" for where such problems actually lie.
#include <iostream>
#include <fstream>
using namespace std;
#define SHOW(X) cout << # X " = \"" << (X) << "\"" << endl
int main()
{
int x = 0;
cin >> x;
ifstream iffer;
int numbers[12];
iffer.open("input.txt");
SHOW( iffer.fail() );
SHOW( iffer.eof() );
for (int i = 0; i < 12; ++i)
{
SHOW(i);
SHOW(numbers[i]);
iffer >> numbers[i];
SHOW(numbers[i]) << endl;
}
for (int i = 0; i < 12; ++i)
SHOW(numbers[i]);
SHOW( iffer.fail() );
SHOW( iffer.eof() );
}

Answer 5

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.