Send ESC commands to a printer in C#

I've blogged about this before after having to do it myself. Not to toot my own horn too loudly, but I recommend that you read that entry, as I talk about a complex image command with the printer. If you can understand that, you can print anything!

(I talk about ESC/POS, used in retail receipt printers, but the semantics of the discussion applies to ESC/P, the older dot-matrix language, as well.)

In short, use a BinaryWriter instead of a string or you'll get hopelessly confused (as I did) as certain characters get "baked" in the wrong encoding on their way to the printer. (Trust me on this one! Do not use a StringBuilder when trying to talk in ESC/POS.)

Be careful not to use the Write(string) overload of the BinaryWriter as it will prepend the length of the string as a byte in the stream, which is not what you want. (I also blogged about that after learning that the hard way, too, on the same project.)

Then I use some code to send the byte array, as obtained from the BinaryWriter, directly to the printer by P/Invoking:

private static void Print(string printerName, byte[] document)
{
    NativeMethods.DOC_INFO_1 documentInfo;
    IntPtr printerHandle;

    documentInfo = new NativeMethods.DOC_INFO_1();
    documentInfo.pDataType = "RAW";
    documentInfo.pDocName = "Bit Image Test";

    printerHandle = new IntPtr(0);

    if (NativeMethods.OpenPrinter(printerName.Normalize(), out printerHandle, IntPtr.Zero))
    {
        if (NativeMethods.StartDocPrinter(printerHandle, 1, documentInfo))
        {
            int bytesWritten;
            byte[] managedData;
            IntPtr unmanagedData;

            managedData = document;
            unmanagedData = Marshal.AllocCoTaskMem(managedData.Length);
            Marshal.Copy(managedData, 0, unmanagedData, managedData.Length);

            if (NativeMethods.StartPagePrinter(printerHandle))
            {
                NativeMethods.WritePrinter(
                    printerHandle,
                    unmanagedData,
                    managedData.Length,
                    out bytesWritten);
                NativeMethods.EndPagePrinter(printerHandle);
            }
            else
            {
                throw new Win32Exception();
            }

            Marshal.FreeCoTaskMem(unmanagedData);

            NativeMethods.EndDocPrinter(printerHandle);
        }
        else
        {
            throw new Win32Exception();
        }

        NativeMethods.ClosePrinter(printerHandle);
    }
    else
    {
        throw new Win32Exception();
    }
}

Good luck!

Bypassing the printer driver and controlling the printer directly, using its native command language, is a supported scenario. The P/Invoke is explained well in this KB article.

Sure you want to do this? It is uncommon, to put it mildly, usually only attempted with low-cost Point-Of-Sale thermal or matrix printers. If you don't like the mechanics of PrintDocument.PrintPage, nobody does, you could consider my code in this thread. Note the FormFeed method.