how to read and parse text files with istringstream?

I am trying to read a .txt file line by line:

vector<vector<int>> iVecGrid;
vector<int> iVecRow;

ifstream text;
text.open("grid.txt", ios::in);

if (!text)
{
    cout << "Error!\n";
    return EXIT_FAILURE;
}

istringstream isLine;
string sLine;
while (getline(text, sLine))
{
    isLine.str(sLine);
    int iNumber;
    while (isLine >> iNumber)
    {
        cout << iNumber << " ";
        iVecRow.push_back(iNumber);
    }
    cout << endl;

    iVecGrid.push_back(iVecRow);
    iVecRow.clear();
}

When I put isLine inside the while (getline(text, sLine)) loop, it works fine.

But when I put it outside, it bugged out for some reason.

.txt file:

08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08
49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00
81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65
52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 91
22 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 80
24 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 50
32 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 70
67 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 21
24 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 72
21 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 95
78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92
16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57
86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58
19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40
04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66
88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69
04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36
20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16
20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54
01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48

Solution

When you are done with the following loop

while (isLine >> iNumber)
{
    cout << iNumber << " ";
    iVecRow.push_back(iNumber);
}

isLine is in a state of error. The error state needs to cleared. Add the following line after the loop.

isLine.clear();

Also, the position of isLine needs to be reset to point to the start of the string. You can use the following line for that.

isLine.seekg(0);

Both of these problems are avoided by moving the scope of isLine to inside the while block.

The following should work.

while (getline(text, sLine))
{
    isLine.str(sLine);
    isLine.seekg(0);   //ADD. Start reading from position 0.

    int iNumber;
    while (isLine >> iNumber)
    {
        cout << iNumber << " ";
        iVecRow.push_back(iNumber);
    }

    isLine.clear();  //ADD. Clear the error state.

    cout << endl;

    iVecGrid.push_back(iVecRow);
    iVecRow.clear();
}

However, I would recommend sticking to your first approach. It removes the unnecessary clutter from your code.

while (getline(text, sLine))
{
    std::istringstream isLine(sLine);

    int iNumber;
    while (isLine >> iNumber)
    {
        cout << iNumber << " ";
        iVecRow.push_back(iNumber);
    }

    cout << endl;

    iVecGrid.push_back(iVecRow);
    iVecRow.clear();
}