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FileStream vs Excel Application

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Not one usually to post non-AutoIt things, but as I have this question on StackExchange I thought I would throw it up here as well for any of our C# folks:

I currently have an AutoIt GUI that calls a powershell script; the intent is to allow low-level technicians to batch create VMs in vSphere. Due to some changes in requirements from the customer, I am re-writing as a wpf app. The app itself is complete and working; this is more of a curiosity question.

I have two methods attached to buttons on the GUI - one to pull all the data out of a listview and export to csv and another to do the reverse; importing from csv to the listview element. I wrote the export first, and went with manipulating the Excel application:

    private void Launch(object sender, RoutedEventArgs e)
        Microsoft.Office.Interop.Excel.Application oExcel = new Microsoft.Office.Interop.Excel.Application();
        oExcel.Visible = true;
        Microsoft.Office.Interop.Excel.Workbook oWorkBook = oExcel.Workbooks.Add(Microsoft.Office.Interop.Excel.XlSheetType.xlWorksheet);
        Microsoft.Office.Interop.Excel.Worksheet oSheet = (Microsoft.Office.Interop.Excel.Worksheet)oExcel.ActiveSheet;

        int row = 2; //allow for header row
        int column = 1;

        oSheet.Cells[1, 1] = "Name";
        oSheet.Cells[1, 2] = "CPU";
        oSheet.Cells[1, 3] = "RAM";
        oSheet.Cells[1, 4] = "IP Address";
        oSheet.Cells[1, 5] = "Subnet Mask";
        oSheet.Cells[1, 6] = "Port Group";
        oSheet.Cells[1, 7] = "Default Gateway";
        oSheet.Cells[1, 8] = "DNS";
        oSheet.Cells[1, 9] = "Description";
        oSheet.Cells[1, 10] = "Template";
        oSheet.Cells[1, 11] = "Host";
        oSheet.Cells[1, 12] = "Site";
        oSheet.Cells[1, 13] = "Folder";
        oSheet.Cells[1, 14] = "DataStore";
        oSheet.Cells[1, 15] = "Patch Method";
        oSheet.Cells[1, 16] = "HDD1Size";
        oSheet.Cells[1, 17] = "HDD1Format";
        oSheet.Cells[1, 18] = "HDD2Size";
        oSheet.Cells[1, 19] = "HDD2Format";
        oSheet.Cells[1, 20] = "HDD3Size";
        oSheet.Cells[1, 21] = "HDD3Format";
        oSheet.Cells[1, 22] = "HDD4Size";
        oSheet.Cells[1, 23] = "HDD4Format";
        oSheet.Cells[1, 24] = "HDD5Size";
        oSheet.Cells[1, 25] = "HDD5Format";

        foreach (var oVM in MyItems)
            oSheet.Cells[row, column] = oVM.Name;
            oSheet.Cells[row, (column + 1)] = oVM.CPU;
            oSheet.Cells[row, (column + 2)] = oVM.RAM;
            oSheet.Cells[row, (column + 3)] = oVM.IP;
            oSheet.Cells[row, (column + 4)] = oVM.Subnet;
            oSheet.Cells[row, (column + 5)] = oVM.PortGroup;
            oSheet.Cells[row, (column + 6)] = oVM.Gateway;
            oSheet.Cells[row, (column + 7)] = oVM.DNS;
            oSheet.Cells[row, (column + 8)] = oVM.Description;
            oSheet.Cells[row, (column + 9)] = oVM.Template;
            oSheet.Cells[row, (column + 10)] = oVM.Host;
            oSheet.Cells[row, (column + 11)] = oVM.Site;
            oSheet.Cells[row, (column + 12)] = oVM.Folder;
            oSheet.Cells[row, (column + 13)] = oVM.Datastore;
            oSheet.Cells[row, (column + 14)] = oVM.Patch;
            oSheet.Cells[row, (column + 15)] = oVM.HDD1Size;
            oSheet.Cells[row, (column + 16)] = oVM.HDD1Format;
            oSheet.Cells[row, (column + 17)] = oVM.HDD2Size;
            oSheet.Cells[row, (column + 18)] = oVM.HDD2Format;
            oSheet.Cells[row, (column + 19)] = oVM.HDD3Size;
            oSheet.Cells[row, (column + 20)] = oVM.HDD3Format;
            oSheet.Cells[row, (column + 21)] = oVM.HDD4Size;
            oSheet.Cells[row, (column + 22)] = oVM.HDD4Format;
            oSheet.Cells[row, (column + 23)] = oVM.HDD5Size;
            oSheet.Cells[row, (column + 24)] = oVM.HDD5Format;

        oExcel.Application.ActiveWorkbook.SaveAs(Environment.GetFolderPath(Environment.SpecialFolder.DesktopDirectory) + "\\example", 6);

It works, but it is slow. I have Excel set to visible for testing, and it is a good 6 or 7 seconds on a pretty high end box before the app even pops up.  It then takes another 2 seconds to populate 11 rows (this could be in the hundreds of rows at some point).

I then wrote the code for the reverse, and decided to try a StreamReader object. The result, surprisingly, was almost immediate:

           OpenFileDialog xls = new OpenFileDialog();
            xls.Multiselect = false;
            xls.Filter = "CSV files (*.csv)|*.csv";
            xls.InitialDirectory = Environment.GetFolderPath(Environment.SpecialFolder.DesktopDirectory);
            string ins;

            if (xls.FileName != null)
                FileStream srcFS;
                srcFS = new FileStream(xls.FileName, FileMode.Open);
                StreamReader srcSR = new StreamReader(srcFS, System.Text.Encoding.Default);
                    ins = srcSR.ReadLine();
                    if (ins != null)
                        string[] parts = ins.Split(',');

                        MyItems.Add(new MyItem
                            Name = parts[0],
                            CPU = parts[1],
                            RAM = parts[2],
                            IP = parts[3],
                            Subnet = parts[4],
                            PortGroup = parts[5],
                            Gateway = parts[6],
                            DNS = parts[7],
                            Description = parts[8],
                            Template = parts[9],
                            Host = parts[10],
                            Site = parts[11],
                            Folder = parts[12],
                            Datastore = parts[13],
                            Patch = parts[14],
                            HDD1Size = parts[15],
                            HDD1Format = parts[16],
                            HDD2Size = parts[17],
                            HDD2Format = parts[18],
                            HDD3Size = parts[19],
                            HDD3Format = parts[20],
                            HDD4Size = parts[21],
                            HDD4Format = parts[22],
                            HDD5Size = parts[23],
                            HDD5Format = parts[24]
                } while (ins != null);


So, I thought I would go back and change the export to use the same method:

        FileStream srcFS;
        srcFS = new FileStream(Environment.GetFolderPath(Environment.SpecialFolder.DesktopDirectory) + "\\testingout.csv", FileMode.CreateNew, FileAccess.Write);
        StreamWriter srcWrt = new StreamWriter(srcFS, System.Text.Encoding.Default);
        StringBuilder header = new StringBuilder();
                  .Append("IP Address").Append(',')
                  .Append("Port Group").Append(',')
                  .Append("Default Gateway").Append(',')


        foreach (MyItem item in MyItems)
            StringBuilder builder = new StringBuilder();

MessageBox.Show("Task Complete");

What surprised me is this method is exponentially slower; on the order of 40 seconds to return the MsgBox. I also noticed that even though the loop is complete and shows the message, is seems the stream is still writing. If I open the file too quickly it shows that it is still in use by "Another User". So by the time the file is available to me it is actually closer to a minute for an 11-line csv.

I'm just curious at the difference in speed read vs write using FileStream. Is it something I borked on implementation (eminently possible) or is this a known issue? If interacting with Excel is the way to go (not ideal) is there something I could do to shorten the initial lag?

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I know NOTHING about c#.

But I noticed a dramatic decrease in execution time when I rewrote the Excel UDF. The old UDF called an Excel method for each cell to write data. The new UDF populates an array and then writes the whole array by calling an Excel method only once.
In your case you should see a 25:1 ratio.
Please check the Excel UDF to get an idea how it would speed up your code :)

My UDFs and Tutorials:


Active Directory (NEW 2019-10-24 - Version - Download - General Help & Support - Example Scripts - Wiki
OutlookEX (NEW 2019-11-30 - Version - Download - General Help & Support - Example Scripts - Wiki
Outlook Tools (2019-07-22 - Version - Download - General Help & Support - Wiki
ExcelChart (2017-07-21 - Version - Download - General Help & Support - Example Scripts
PowerPoint (2017-06-06 - Version - Download - General Help & Support
Excel - Example Scripts - Wiki
Word - Wiki
Task Scheduler (NEW 2019-12-03 - Version - Download - General Help & Support - Wiki

ADO - Wiki


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Thanks, water, I was just doing that actually. The conversion from list view object to array is giving me fits, but it looks like that may be a bether way to go. Still strange why Filestream is so slow.

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have you tried this person's answer on stack exchange?


and at GitHub, and Excel Data Reader


Edited by Earthshine

My resources are limited. You must ask the right questions


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It ended up being a case of blatant stupidity. With the WriteLine inside the loop of course it was going to slow down. By doing it properly, building the entire StringBuilder object and then writing only once, it completes 1000 rows by 25 columns in about 2 seconds.

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