Printing to LPT1 in C#

Question

How do you print directly to a dot matrix printer in C# using file LPT1.

I did it on C++ with fopen, but I don\'t know how to do it in c#.

thank you very much

Answer 1

Set up the printer in Windows as Generic/Text Only, then print to it.

Here's the code I use to print to a label printer that has its own encoded text format.

using System;
using System.Collections.Generic;
using System.Text;
using System.Drawing;
using System.Drawing.Printing;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.IO;

namespace whatever {

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, IntPtr 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, IntPtr 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 = "My C#.NET RAW Document";
        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();
        }
        return bSuccess;
    }

    public static bool SendFileToPrinter(string szPrinterName, string szFileName)
    {
        // Open the file.
        FileStream fs = new FileStream(szFileName, FileMode.Open);
        // Create a BinaryReader on the file.
        BinaryReader br = new BinaryReader(fs);
        // Dim an array of bytes big enough to hold the file's contents.
        Byte[] bytes = new Byte[fs.Length];
        bool bSuccess = false;
        // Your unmanaged pointer.
        IntPtr pUnmanagedBytes = new IntPtr(0);
        int nLength;

        nLength = Convert.ToInt32(fs.Length);
        // Read the contents of the file into the array.
        bytes = br.ReadBytes(nLength);
        // Allocate some unmanaged memory for those bytes.
        pUnmanagedBytes = Marshal.AllocCoTaskMem(nLength);
        // Copy the managed byte array into the unmanaged array.
        Marshal.Copy(bytes, 0, pUnmanagedBytes, nLength);
        // Send the unmanaged bytes to the printer.
        bSuccess = SendBytesToPrinter(szPrinterName, pUnmanagedBytes, nLength);
        // Free the unmanaged memory that you allocated earlier.
        Marshal.FreeCoTaskMem(pUnmanagedBytes);
        return bSuccess;
    }
    public static bool SendStringToPrinter(string szPrinterName, string szString)
    {
        IntPtr pBytes;
        Int32 dwCount;
        // How many characters are in the string?
        dwCount = szString.Length;
        // Assume that the printer is expecting ANSI text, and then convert
        // the string to ANSI text.
        pBytes = Marshal.StringToCoTaskMemAnsi(szString);
        // Send the converted ANSI string to the printer.
        bool success = SendBytesToPrinter(szPrinterName, pBytes, dwCount);
        Marshal.FreeCoTaskMem(pBytes);
        return success;
    }
}
}

Then this is called from another class like this:

    private bool PrintLabels(string printerName)
    {
        return RawPrinterHelper.SendStringToPrinter(printerName, this.Text);
    }

(edit: if anyone sees any major fubars related to unmanaged resources, let me know in the comments)

Answer 2

Maybe you cannot print to the device "LPT1" but to a "dumb teletype printer" that you have to install first. If they exist in modern windows.... So you should print to "mydumbprinter" which in its turn uses LPT1 as printer port. It appeared to me as I followed the Source link by Cocowalla above - there you select a printer in a PrinterDialog. The resulting printer name would more likely be "Laserjet" than "LPT1".

Answer 3

In C# its possible, first you need to connect to that port using the CreateFile method then open a filestream to that port to finally write to it. Here is a sample class that writes two lines to the printer on LPT1.

using Microsoft.Win32.SafeHandles;
using System;
using System.IO;
using System.Runtime.InteropServices;

namespace YourNamespace
{
public static class Print2LPT
        {
            [DllImport("kernel32.dll", SetLastError = true)]
            static extern SafeFileHandle CreateFile(string lpFileName, FileAccess dwDesiredAccess,uint dwShareMode, IntPtr lpSecurityAttributes, FileMode dwCreationDisposition, uint dwFlagsAndAttributes, IntPtr hTemplateFile);

            public static bool Print()
            {
                string nl = Convert.ToChar(13).ToString() + Convert.ToChar(10).ToString();
                bool IsConnected= false;

                string sampleText ="Hello World!" + nl +
                "Enjoy Printing...";     
                try
                {
                    Byte[] buffer = new byte[sampleText.Length];
                    buffer = System.Text.Encoding.ASCII.GetBytes(sampleText);

                    SafeFileHandle fh = CreateFile("LPT1:", FileAccess.Write, 0, IntPtr.Zero, FileMode.OpenOrCreate, 0, IntPtr.Zero);
                    if (!fh.IsInvalid)
                    {
                        IsConnected= true;                    
                        FileStream lpt1 = new FileStream(fh,FileAccess.ReadWrite);
                        lpt1.Write(buffer, 0, buffer.Length);
                        lpt1.Close();
                    }

                }
                catch (Exception ex)
                {
                    string message = ex.Message;
                }

                return IsConnected;
            }
        }
}

Assuming your printer is connected on the LPT1 port, if not you will need to adjust the CreateFile method to match the port you are using.

you can call the method anywhere in your program with the following line

Print2LPT.Print();

I think this is the shortest and most efficient solution to your problem.