Send String to Command Prompt (cmd) from Windows Form Application using SendMessage

Question

I read many answers on how to send command to cmd prompt.

But I do not want to use StreamWriter or similar stuff to input and get output.

I want to use SendMessage to send my string or say command to the cmd prompt window.

Can anyone please help on this?

Just to give detail about my application. 1. My application is a WinForm App. 2. It has 4-5 buttons. 3. Button1 opens the command prompt window while Button5 closes or exits the command prompt window. 4. Button 2,3,4 are command buttons. When user clicks the Button2 command 1 is send to command prompt window. Similar when button 3 and 4 are clicked command 2 and command 3 are sent to the same command prompt window.

Let me know if anybody has a written code which sends string to command prompt.

Thanks and regards,

Rahul

Answer 1

I have got the solution.
I used PostMessage().
Cmd has handle and you can send string to it.
I was just struggling to find the right way to get the handle.
Now I got one.

/*
 * Created by SharpDevelop.
 * User: Rahul
 * Date: 5/12/2011
 * Time: 1:49 AM
 * 
 * To change this template use Tools | Options | Coding | Edit Standard Headers.
 */
using System;
using System.Collections.Generic;
using System.Drawing;
using System.Windows.Forms;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Text;

namespace GetChildWindows
{
/// <summary>
/// Description of MainForm.
/// </summary>
public partial class MainForm : Form
{
    [DllImport("user32")]
    [return: MarshalAs(UnmanagedType.Bool)]
    public static extern bool EnumChildWindows(IntPtr window, EnumWindowProc callback, IntPtr i);

    [DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Auto)]
    static extern int GetClassName(IntPtr hWnd, StringBuilder lpClassName, int nMaxCount);

    [DllImport("user32.dll", SetLastError = true)]
    static extern IntPtr FindWindow(string lpClassName, string lpWindowName);
    IntPtr hWnd = FindWindow(null, "Untitled - Notepad");

    [DllImport("user32.dll", SetLastError = true)]
    static extern bool PostMessage(IntPtr hWnd, [MarshalAs(UnmanagedType.U4)] uint Msg, IntPtr wParam, IntPtr lParam);


    [DllImport("user32.dll", SetLastError = true)]
    static extern bool PostMessage(IntPtr hWnd, [MarshalAs(UnmanagedType.U4)] uint Msg, int wParam, int lParam);        

    const int WM_KEYDOWN = 0x0100;
    const int WM_KEYUP = 0x0101;
    const int WM_CHAR = 0x0102;

    public static IntPtr cmdHwnd = IntPtr.Zero;

    public MainForm()
    {
        //
        // The InitializeComponent() call is required for Windows Forms designer support.
        //
        InitializeComponent();

        //
        // TODO: Add constructor code after the InitializeComponent() call.
        //

        foreach (IntPtr child in GetChildWindows(FindWindow(null, "WinPlusConsole")))
        {
            StringBuilder sb = new StringBuilder(100);
            GetClassName(child, sb, sb.Capacity);


            if (sb.ToString() == "ConsoleWindowClass")
            {
//                  uint wparam = 0 << 29 | 0;
//                  string msg = "Hello";
//                  int i = 0;
//                  for (i = 0 ; i < msg.Length ; i++)
//                  {
//                      //PostMessage(child, WM_KEYDOWN, (IntPtr)Keys.Enter, (IntPtr)wparam);
//                      PostMessage(child, WM_CHAR, (int)msg[i], 0);
//                  }
//                  PostMessage(child, WM_KEYDOWN, (IntPtr)Keys.Enter, (IntPtr)wparam);

                cmdHwnd = child;
            }
        }

}

/// <summary>
    /// Returns a list of child windows
    /// </summary>
    /// <param name="parent">Parent of the windows to return</param>
    /// <returns>List of child windows</returns>
    public static List<IntPtr> GetChildWindows(IntPtr parent)
    {
        List<IntPtr> result = new List<IntPtr>();
        GCHandle listHandle = GCHandle.Alloc(result);
        try
        {
            EnumWindowProc childProc = new EnumWindowProc(EnumWindow);
            EnumChildWindows(parent, childProc, GCHandle.ToIntPtr(listHandle));
        }
        finally
        {
            if (listHandle.IsAllocated)
            listHandle.Free();
        }
        return result;
    }

    /// <summary>
    /// Callback method to be used when enumerating windows.
    /// </summary>
    /// <param name="handle">Handle of the next window</param>
    /// <param name="pointer">Pointer to a GCHandle that holds a reference to the list to fill</param>
    /// <returns>True to continue the enumeration, false to bail</returns>

    private static bool EnumWindow(IntPtr handle, IntPtr pointer)
    {
        GCHandle gch = GCHandle.FromIntPtr(pointer);
        List<IntPtr> list = gch.Target as List<IntPtr>;
        if (list == null)
        {
            throw new InvalidCastException("GCHandle Target could not be cast as List<IntPtr>");
        }
        list.Add(handle);
        // You can modify this to check to see if you want to cancel the operation, then return a null here
        return true;
    }

    /// <summary>
    /// Delegate for the EnumChildWindows method
    /// </summary>
    /// <param name="hWnd">Window handle</param>
    /// <param name="parameter">Caller-defined variable; we use it for a pointer to our list</param>
    /// <returns>True to continue enumerating, false to bail.</returns>
    public delegate bool EnumWindowProc(IntPtr hWnd, IntPtr parameter);





    void BtnHelloClick(object sender, EventArgs e)
    {
        uint wparam = 0 << 29 | 0;
                string msg = "Hello";
                int i = 0;
                for (i = 0 ; i < msg.Length ; i++)
                {
                    //PostMessage(child, WM_KEYDOWN, (IntPtr)Keys.Enter, (IntPtr)wparam);
                    PostMessage(cmdHwnd, WM_CHAR, (int)msg[i], 0);
                }
                PostMessage(cmdHwnd, WM_KEYDOWN, (IntPtr)Keys.Enter, (IntPtr)wparam);
    }

    void BtnCommandClick(object sender, EventArgs e)
    {
        uint wparam = 0 << 29 | 0;
                string msg = textBox1.Text;
                int i = 0;
                for (i = 0 ; i < msg.Length ; i++)
                {
                    //PostMessage(child, WM_KEYDOWN, (IntPtr)Keys.Enter, (IntPtr)wparam);
                    PostMessage(cmdHwnd, WM_CHAR, (int)msg[i], 0);
                }
                PostMessage(cmdHwnd, WM_KEYDOWN, (IntPtr)Keys.Enter, (IntPtr)wparam);
    }

    void TextBox1TextChanged(object sender, EventArgs e)
    {

    }
}
} 

Thanks to all!

Answer 2

It seems unlikely that you would be able to achieve this with SendMessage() . SendMessage() requires a window handle and I don't believe that cmd.exe has a suitable window handle to receive the message.

My advice is to look for a method that solves your problem rather than deciding what solution you want and trying to make it fit the problem.

Answer 3

its not clear from your explenation (at least not to me) why you cant use streamWriter in the scenario you describe. can you elaborate on that?

i'd check out the Process class for talking to other programs via stdin/out