'System.AccessViolationException' occurred


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Jul 13, 2015
Programming Experience
UPDATE : I found a weird anomaly. The code has now been continuously breaking on that line, when the tabName variable equals "service line prior year". This morning, for grins, I changed the tab name to "test", so in turn the tabName variable equals "test", and it worked more often then not. I am really at a loss.

This was asked on StackOverflow, by me, but I am no closer to an answer, so I wanted to try here, too. I have researched a ton and can't find anything that addresses what is happening in my code. It happens randomly though. Sometimes it doesn't happen, then other times it happens in the same spot, but all on this part of the code (on the line templateSheet = templateBook.Sheets[tabName];):

     public void ExportToExcel(DataSet dataSet, string filePath, int i, int h, Excel.Application excelApp)
                //create the excel definitions again.
                //Excel.Application excelApp = new Excel.Application();
                //excelApp.Visible = true;
                FileInfo excelFileInfo = new FileInfo(filePath);
                Boolean fileOpenTest = IsFileOpen(excelFileInfo);

                Excel.Workbook templateBook;
                Excel.Worksheet templateSheet;
                //check to see if the template is already open, if its not then open it,
                //if it is then bind it to work with it
                if (!fileOpenTest)
                { templateBook = excelApp.Workbooks.Open(filePath); }
                { templateBook = (Excel.Workbook)System.Runtime.InteropServices.Marshal.BindToMoniker(filePath); }

                //this grabs the name of the tab to dump the data into from the "Query Dumps" Tab
                    string tabName = lstQueryDumpSheet.Items[i].ToString();
                    templateSheet = templateBook.Sheets[tabName];
                    excelApp.Calculation = Excel.XlCalculation.xlCalculationManual;

                    templateSheet = templateBook.Sheets[tabName];        

                // Copy DataTable
                foreach (System.Data.DataTable dt in dataSet.Tables)
                    // Copy the DataTable to an object array
                    object[,] rawData = new object[dt.Rows.Count + 1, dt.Columns.Count];

                    // Copy the values to the object array
                    for (int col = 0; col < dt.Columns.Count; col++)
                        for (int row = 0; row < dt.Rows.Count; row++)
                        { rawData[row, col] = dt.Rows[row].ItemArray[col]; }

                    // Calculate the final column letter
                    string finalColLetter = string.Empty;
                    string colCharset = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
                    int colCharsetLen = colCharset.Length;

                    if (dt.Columns.Count > colCharsetLen)
                    { finalColLetter = colCharset.Substring((dt.Columns.Count - 1) / colCharsetLen - 1, 1); }

                    finalColLetter += colCharset.Substring((dt.Columns.Count - 1) % colCharsetLen, 1);

                    //this grabs the cell address from the "Query Dump" sheet, splits it on the '=' and
                    //pulls out only the cell address (i.e., "address=a3" becomes "a3")
                    string dumpCellString = lstQueryDumpText.Items[i].ToString();
                    string dumpCell = dumpCellString.Split('=').Last();

                    //referts to the range in which we are dumping the DataSet.  The upper right hand cell is
                    //defined by the 'dumpCell' varaible and the bottom right cell is defined by the 
                    //final column letter and the count of rows.
                    string firstRef = "";
                    string baseRow = "";

                    if (char.IsLetter(dumpCell, 1))
                        char[] createCellRef = dumpCell.ToCharArray();
                        firstRef = createCellRef[0].ToString() + createCellRef[1].ToString();
                        for (int z = 2; z < createCellRef.Count(); z++)
                            baseRow = baseRow + createCellRef[z].ToString();
                        char[] createCellRef = dumpCell.ToCharArray();
                        firstRef = createCellRef[0].ToString();
                        for (int z = 1; z < createCellRef.Count(); z++)
                            baseRow = baseRow + createCellRef[z].ToString();

                    int baseRowInt = Convert.ToInt32(baseRow);
                    int startingCol = ColumnLetterToColumnIndex(firstRef);
                    int endingCol = ColumnLetterToColumnIndex(finalColLetter);

                    int finalCol = startingCol + endingCol;
                    string endCol = ColumnIndexToColumnLetter(finalCol - 1);
                    int endRow = (baseRowInt + (dt.Rows.Count - 1));
                    string cellCheck = endCol + endRow;
                    string excelRange;

                    if (dumpCell.ToUpper() == cellCheck.ToUpper())
                        excelRange = string.Format(dumpCell + ":" + dumpCell);
                        excelRange = string.Format(dumpCell + ":{0}{1}", endCol, endRow);

                    //this dumps the cells into the range on Excel as defined above
                    templateSheet.get_Range(excelRange, Type.Missing).Value2 = rawData;

                    //checks to see if all the SQL queries have been run from the "Query Dump" tab, if not, continue 
                    //the loop, if it is the last one, then save the workbook and move on.

                    if (i == lstSqlAddress.Items.Count - 1)
                        excelApp.Calculation = Excel.XlCalculation.xlCalculationAutomatic;

                        /*Run through the value save sheet array then grab the address from the corresponding list 
                        place in the address array.  If the address reads "whole sheet" then save the whole page,
                        else set the addresses range and value save that.*/
                        //for (int y = 0; y < lstSaveSheet.Items.Count; y++)
                        //    MessageBox.Show("Save Sheet: " + lstSaveSheet.Items[y] + "\n" + "Save Address: " + lstSaveRange.Items[y]);

                        //run the macro to hide the unused columns

                        //save excel file as hospital name and move onto the next
                        SaveTemplateAs(templateBook, h);

                        //close the open Excel App before looping back
                        //templateSheet = null;
                        //templateBook = null;
                    //Close excel Applications
                    //excelApp = null;
                    //templateSheet = null;
                    // GC.Collect();
The try/catch block is of no use either. This is the error:

"An unhandled exception of type 'System.AccessViolationException' occurred inSQUiRE (Sql QUery REtriever) v1.exe. Additional information: Attempted to read or write protected memory. This is often an indication that other memory is corrupt."
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