title: How to print QR Code using Commands with Zebra RW 420 thermal printer via USB in C#
body: <blockquote>
    <p>Before you go on and flag my question as a duplicate, believe me, its
    not. I have gone through virtually every solution provided here and I
    still can't get to get my app to work, so please will you just be nice
    and take some time to help me.</p>
  </blockquote>
  
  <p>Scenario: I have a Zebra RW 420 thermal printer which I would like to use for printing vouchers with a QR Code on them. I am using C# and have followed all the help as given by <a href="https://stackoverflow.com/questions/25669403/how-to-send-a-raw-zpl-to-zebra-printer-using-c-sharp-via-usb">Scott Chamberlain here</a> and the <a href="http://support.microsoft.com/kb/322091" rel="nofollow noreferrer">code here</a> for sending the commands to the printer. I have the EPL2 manual as well as the CPCL, and ZPL reference manuals with a whole lot of stuff on how to format my commands.</p>
  
  <p>Problem:
  All the commands I am sending are either printing as plain text replicas of the commands or the printer just hangs with the small message icon showing on its display. I have tried sending the same commands using the Zebra Utilitis and still getting the same result as with my sample app.
  Below is the code snippets I have, please do advise me if there are any reference libraries I may require to get this to work.</p>
  
  <pre><code>private void btnPrint_Click(object sender, RoutedEventArgs e)
      {
          string s = "! 0 200 200 500 1\nB QR 10 100 M 2 U 10\nMA,QR code ABC123\nENDQR\nFORM\nPRINT"; 
  </code></pre>
  
  <p>// Have also tried \r\n for the line feeds with the same result.</p>
  
  <pre><code>        // Allow the user to select a printer.
          PrintDialog pd = new PrintDialog();
  
          if ((bool)pd.ShowDialog())
          {
              var bytes = Encoding.ASCII.GetBytes(s);
              // Send a printer-specific to the printer.
              RawPrinterHelper.SendBytesToPrinter(pd.PrintQueue.FullName, bytes, bytes.Length);
          }
      }
  </code></pre>
  
  <p>PrinterHelper class as modified by <a href="https://stackoverflow.com/questions/25669403/how-to-send-a-raw-zpl-to-zebra-printer-using-c-sharp-via-usb">Scott here</a></p>
  
  <pre><code>public class RawPrinterHelper
  {
      // Structure and API declarions:
      [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
      public class DOCINFOA
      {
          [MarshalAs(UnmanagedType.LPStr)] public string pDocName;
          [MarshalAs(UnmanagedType.LPStr)] public string pOutputFile;
          [MarshalAs(UnmanagedType.LPStr)] public string pDataType;
      }
  
      [DllImport("winspool.Drv", EntryPoint = "OpenPrinterA", SetLastError = true, CharSet = CharSet.Ansi,
          ExactSpelling = true, CallingConvention = CallingConvention.StdCall)]
      public static extern bool OpenPrinter([MarshalAs(UnmanagedType.LPStr)] string szPrinter, out IntPtr hPrinter,
          IntPtr pd);
  
      [DllImport("winspool.Drv", EntryPoint = "ClosePrinter", SetLastError = true, ExactSpelling = true,
          CallingConvention = CallingConvention.StdCall)]
      public static extern bool ClosePrinter(IntPtr hPrinter);
  
      [DllImport("winspool.Drv", EntryPoint = "StartDocPrinterA", SetLastError = true, CharSet = CharSet.Ansi,
          ExactSpelling = true, CallingConvention = CallingConvention.StdCall)]
      public static extern bool StartDocPrinter(IntPtr hPrinter, Int32 level,
          [In, MarshalAs(UnmanagedType.LPStruct)] DOCINFOA di);
  
      [DllImport("winspool.Drv", EntryPoint = "EndDocPrinter", SetLastError = true, ExactSpelling = true,
          CallingConvention = CallingConvention.StdCall)]
      public static extern bool EndDocPrinter(IntPtr hPrinter);
  
      [DllImport("winspool.Drv", EntryPoint = "StartPagePrinter", SetLastError = true, ExactSpelling = true,
          CallingConvention = CallingConvention.StdCall)]
      public static extern bool StartPagePrinter(IntPtr hPrinter);
  
      [DllImport("winspool.Drv", EntryPoint = "EndPagePrinter", SetLastError = true, ExactSpelling = true,
          CallingConvention = CallingConvention.StdCall)]
      public static extern bool EndPagePrinter(IntPtr hPrinter);
  
      [DllImport("winspool.Drv", EntryPoint = "WritePrinter", SetLastError = true, ExactSpelling = true,
          CallingConvention = CallingConvention.StdCall)]
      public static extern bool WritePrinter(IntPtr hPrinter, byte[] pBytes, Int32 dwCount, out Int32 dwWritten);
  
      // SendBytesToPrinter()
      // When the function is given a printer name and an unmanaged array
      // of bytes, the function sends those bytes to the print queue.
      // Returns true on success, false on failure.
      public static bool SendBytesToPrinter(string szPrinterName, byte[] pBytes, Int32 dwCount)
      {
          Int32 dwError = 0, dwWritten = 0;
          IntPtr hPrinter = new IntPtr(0);
          DOCINFOA di = new DOCINFOA();
          bool bSuccess = false; // Assume failure unless you specifically succeed.
  
          di.pDocName = "Zebra Label";
          di.pDataType = "RAW";
  
          // Open the printer.
          if (OpenPrinter(szPrinterName.Normalize(), out hPrinter, IntPtr.Zero))
          {
              // Start a document.
              if (StartDocPrinter(hPrinter, 1, di))
              {
                  // Start a page.
                  if (StartPagePrinter(hPrinter))
                  {
                      // Write your bytes.
                      bSuccess = WritePrinter(hPrinter, pBytes, dwCount, out dwWritten);
                      EndPagePrinter(hPrinter);
                  }
                  EndDocPrinter(hPrinter);
              }
              ClosePrinter(hPrinter);
          }
          // If you did not succeed, GetLastError may give more information
          // about why not.
          if (bSuccess == false)
          {
              dwError = Marshal.GetLastWin32Error();
              throw new Win32Exception(dwError);
          }
          return bSuccess;
      }
  </code></pre>
  
  <p>}</p>