How can I fix error when adding elements to my array

Question

I am trying to add elements to my file using a method I have already used and was proven to be successful, however now when I do it I get the numbers I want as well as a bunch of other numbers that aren't in my file and don't make any sense

const int MAX_SIZE = 21;

int readSquare(int square[MAX_SIZE][MAX_SIZE], string inputFileName){ //reads file into an array

    int value;

    ifstream inFile;
    inFile.open(inputFileName);

    if (inFile) //if the input file to be read open successfully then goes on
    {
        int temp;
        inFile >> temp;

        if (temp>21) {
            temp=21;
        }
        for (int i = 0; i < MAX_SIZE; i++)
        {
            for(int j = 0; j < MAX_SIZE; j++)
            {
                inFile >> square[i][j];
            }
        }

    } else {
        inFile.close();
        return 0; //returns 0 if couldnt open file
    }
    inFile.close();

    cout << "Magic square" << endl;
    for(int i=0;i<MAX_SIZE;i++)
    {
        for(int j=0;j<MAX_SIZE;j++)
        {
            cout << square[i][j] << " ";
        }
        cout<<endl;
    }
    return 1;
}

This is the file I am using on my code

And this is the result I get(goes on for a while but I only took the top portion)

4 9 2 3 5 7 8 1 6 16840768 6619136 6643024 23198772 0 1942212500 127 917504 6643024 786434 6643032 0
65536 30 0 31 0 13930549 30 593 6619744 6619744 -2 127 46 6420808 1997546816 -1759127226 -2 6420704 1997359545 4096 4104
0 6420680 6634144 6619136 6421232 4104 6619744 0 3 0 4096 6420732 1997535944 6420804 655612 655360 2 9 0 2 6420976
0 1997378284 6420976 663276 1952 229640288 663200 655360 0 1997377793 6421060 661336 9 16777596 0 13080 236 661336 2 16777596 -530786634

https://ericlippert.com/2014/03/05/how-to-debug-small-programs/ — melpomene, Dec 10 '18 at 03:02
@bvj The first line tells me how many lines are in the file, I do not want that added to the array and I'm setting a max row of 21. Also melpomene I already tried debugging using those standards. I think I am missing something — Unknownzdx, Dec 10 '18 at 03:05
@Unknownzdx bvj didn't ask about the first line, but the variable `temp`. What is your code actually doing with `temp`? — melpomene, Dec 10 '18 at 03:10
@melpomene It grab the first line of the file in the text and if the value is greater then 21, then it sets it to 21. It doesnt do anything besides that — Unknownzdx, Dec 10 '18 at 03:14
@Unknownzdx Why bother setting the value to 21 if you're not doing anything with it? — melpomene, Dec 10 '18 at 03:15
I plan on doing something with it, just trying to fix this problem first — Unknownzdx, Dec 10 '18 at 03:21
As far as I can tell, your code is doing exactly what you told it to do. Which part of its behavior surprises you? — melpomene, Dec 10 '18 at 03:23
All the numbers that come after 6 are not in the file that I put above the output, I do not want them — Unknownzdx, Dec 10 '18 at 03:24
Based on the code I wrote only the first 9 values should have been out — Unknownzdx, Dec 10 '18 at 03:27
Really? Which part of the code limits the output to 9 values? — melpomene, Dec 10 '18 at 03:28
inFile >> square[i][j]; only reads the content of the file and nothing more, yet in the output more has appeared — Unknownzdx, Dec 10 '18 at 03:30
We were talking about the output. `inFile >> square[i][j]` doesn't output anything, so it's not really relevant. — melpomene, Dec 10 '18 at 03:32
You are right, I assumed that something was being read and and being added to the array, thank you — Unknownzdx, Dec 10 '18 at 03:34

score 1 · Accepted Answer · answered Dec 10 '18 at 05:15

Hat tip to @melpomene for working through the details in the main comments.

Op, you're iterating over the entire range of the array regardless of the availability of input data. I suggest you do the following so the results are less random in appearance:

initialize the values in the 2D array to zero.
limit the input samples to the quantity you're expecting, and not to exceed the size of the array in either dimension.

In your post, you're showing the value of 3 in the first line of the input file. What does that mean -- 3 lines, 3 samples, or 3 samples for each of the 3 lines?

Since the input file has 3 samples per line, I'm guessing the initial value in the data file represents the samples per line where the values for each line are assigned to an individual inner array.

Without deviating too much from your post, consider the following:

// clear the array for easier diags
for (int n = 0; n < MAX_SIZE; n++)
  for (int m = 0; m < MAX_SIZE; m++)
    square[n][m] = 0;

int cols;

inFile >> cols; // first line of data file indicating the samples in each row

if (cols > MAX_SIZE) // don't exceed the size of the inner array
  cols = MAX_SIZE;

for (int i = 0; i < MAX_SIZE; i++)
{
    for(int j = 0; j < cols; j++)
    {
        if (!(inFile >> square[i][j])) //  read until EOF
        {
          i = MAX_SIZE; // force outer loop to terminate since break only affects the inner loop.
          break;
        }
    }
}

See How does ifstream's eof() work?

How can I fix error when adding elements to my array

1 Answers1