Getline Randomly Stops Working

Question

I am trying to write a very basic program to read in a CSV and display it. The function, as you can see below, is a very basic one. It uses getline to read in each row (until the newline chracter) before displaying each cell. It was working fine and I was finetuning the loop to display each cell when getline simply stopped working. Without changing any of the code to do with getline, I compiled it and it would not read from the file. row is always empty. However, the ifstream is valid because the "test" string (which I inserted in response) reads in from sheet fine. Can anyone help me?

PS: I have had similar problems with getline before. Is it something to do with my system? It seems to work on and off

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

using namespace std;

int main(int argc, char *argv[])
{
ifstream sheet( "StockTake.csv", ios::app );
if ( ! sheet.is_open() )
{
    cout << "Cannot Open File!\n";
    return 0;
}
else
{
    cout << "Opened File\n";
}
//Now print each row (find the newline chracter at the end of each line)
/*string test;
sheet >> test;
cout << test;*/
for ( string row; ! sheet.eof(); getline(sheet, row, '\n') )
{
    if (row == "")
    {
        cout << "Bad Read.  Exiting\n";
        return 0;
    }
    //Print out each row with a tab space between each cell
    string cell;
    //find the beginning and the end of each cell
    for (int i = 0, j = 0; ; )
    {
        /*Checks if the cell is enclosed in quotes
        The first time, j == i hence the -2 and +2
        the +2 is required to "skip" out the apostrophes if
        they are found*/
        if (row.at(i) == '"')
        {
            i++;
            j = i-2;
            do
            {
                j = row.find('"', j+2);
            } while (row.at(j+1) == '"');
            /*Check for the "" apostrophe sign*/
        }
        else
        {
            j = row.find(',', i);
        }
        /*Print the Cell*/
        if (j == string::npos) //if this is the last cell
        {
            cell = row.substr(i, row.size() - i);
        }
        else if ( j-i != 0)
        {
            cell = row.substr(i, j-i);
        }
        else
        {
            cell = "";
        }
        /*Check for the "" apostrophe sign, and replace
        with " for each instance*/
        if ( cell.find("\"\"", 0) != string::npos )
        {
            int pos = -2; //must start at zero
            do
            {
                //Skips out the "current" apostrophe
                //if there are more than one
                pos = cell.find("\"\"", pos+2);
                cell = cell.substr(0, pos) + 
                       cell.substr(pos+1, cell.size()- (pos+1) );
            } while (cell.find("\"\"", pos+2) != string::npos);

        }
        /*Display the Cell, only the space will be displayed
        if the cell is empty*/
        cout << cell << "     ";
        /*Find the next cell*/
        if ( row.at(j) == '"' )
        {
            i = j+2;
        }
        else
        {
            i = j+1;
        }

    }
    cout << "\n"; //Print newline character at the end of each line
}
return 0;
}