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How to send message from C# to C++ (MESSAGE ONLY WINDOW) using SendMessage (WM_COPYDATA)?

EDIT: I GOT IT FIXED HERE'S MY WORKING FULL CODES TO SET EXAMPLE TO NEW FRIENDS and my original question is below too.
before the codes let me introduce you to some docs (in order):
https://learn.microsoft.com/en-us/windows/win32/winmsg/about-messages-and-message-queues#message-routing
https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-sendmessage
https://learn.microsoft.com/en-us/windows/win32/winmsg/window-features#message-only-windows
https://learn.microsoft.com/en-us/windows/win32/dataxchg/using-data-copy
http://pinvoke.net/default.aspx/Structures/COPYDATASTRUCT.html
C# program
using System;
using System.Windows.Forms;
using System.Diagnostics;
using System.Runtime.InteropServices;
namespace Program
{
public partial class Form1 : Form
{
[DllImport("user32.dll")]
static extern long SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);
[DllImport("user32.dll", CharSet = CharSet.Unicode)]
static extern IntPtr FindWindow(string classname, string windowname);
[StructLayout(LayoutKind.Sequential)]
struct COPYDATASTRUCT
{
public uint dwData;
public int cbData;
public IntPtr lpData;
}
public static IntPtr IntPtrAlloc<T>(T param)
{
IntPtr retval = Marshal.AllocHGlobal(Marshal.SizeOf(param));
Marshal.StructureToPtr(param, retval, false);
return (retval);
}
public static void IntPtrFree(IntPtr preAllocated)
{
if (IntPtr.Zero == preAllocated) throw (new Exception("Go Home"));
Marshal.FreeHGlobal(preAllocated); preAllocated = IntPtr.Zero;
}
const int WM_COPYDATA = 0x004A;
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
Thread.Sleep(3000);
string message = "This is a test";
IntPtr hWnd = FindWindow("MyClass", "MyTitle");
if (hWnd == IntPtr.Zero)
{
MessageBox.Show("couldn't find the window");
}
else
{
COPYDATASTRUCT cds;
cds.dwData = 1;
cds.cbData = message.Length + 1;
cds.lpData = Marshal.StringToHGlobalAnsi(message);
IntPtr cdsBuffer = IntPtrAlloc(cds);
SendMessage(hWnd, WM_COPYDATA, IntPtr.Zero, cdsBuffer);
IntPtrFree(cds.lpData);
IntPtrFree(cdsBuffer);
}
}
}
}
C++ program
#include <iostream>
#include <Windows.h>
using namespace std;
LRESULT CALLBACK WindProc(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam)
{
if (Msg == WM_COPYDATA)
{
PCOPYDATASTRUCT data = (PCOPYDATASTRUCT)lParam;
MessageBoxA(hWnd, (LPSTR)data->lpData, "info", 0); // The character set depends on the characters you send
PostQuitMessage(0);
return 0;
}
return DefWindowProc(hWnd, Msg, wParam, lParam);
}
int main(){
WNDCLASSEX wcx = { 0 };
wcx.cbSize = sizeof(WNDCLASSEX);
wcx.lpfnWndProc = WindProc;
wcx.hInstance = GetModuleHandle(NULL);
wcx.lpszClassName = TEXT("MyClass");
RegisterClassEx(&wcx);
HWND hWnd = CreateWindowEx(0, TEXT("MyClass"), TEXT("MyTitle"), 0, 0, 0, 0, 0, HWND_MESSAGE, NULL, GetModuleHandle(NULL), NULL);
MSG message;
for(int i = 0; i < 1000; i++)
{
std::cout << "working" << std::endl;
Sleep(2 * 1000);
if(PeekMessage(&message, NULL, 0, 0, PM_NOREMOVE))
{
break;
}
}
int x;
cout<<"got it!";
cin>>x;
return 0;
}
ORGINIAL QUESTION:
I have a C# application that i want to communicate with a c++ process that i create within my C# app.
I have a code in my hand that is supposed to work i suppose but it doesn't. The message simply is not gotten by c++ app.
my C# program:
namespace ScannerGUI
{
public partial class Form1 : Form
{
[return: MarshalAs(UnmanagedType.Bool)]
[DllImport("user32.dll")]
static extern bool PostMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);
[StructLayout(LayoutKind.Sequential)]
struct COPYDATASTRUCT
{
public uint dwData;
public int cbData;
public IntPtr lpData;
}
public static IntPtr IntPtrAlloc<T>(T param)
{
IntPtr retval = Marshal.AllocHGlobal(Marshal.SizeOf(param));
Marshal.StructureToPtr(param, retval, false);
return (retval);
}
public static void IntPtrFree(IntPtr preAllocated)
{
if (IntPtr.Zero == preAllocated) throw (new Exception("Go Home"));
Marshal.FreeHGlobal(preAllocated); preAllocated = IntPtr.Zero;
}
const int WM_COPYDATA = 0x004A;
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
//creating child process
var prcsInfo = new ProcessStartInfo
{
UseShellExecute=true,
CreateNoWindow = false,
FileName = "main.exe",
};
Process myProcess = Process.Start(prcsInfo);
ChildProcessTracker.AddProcess(myProcess);
Thread.Sleep(3000);
string message = "This is a test";
IntPtr hWnd = myProcess.Handle;
if (hWnd == IntPtr.Zero)
{
MessageBox.Show("couldn't find the process");
}
else
{
COPYDATASTRUCT cds;
cds.dwData = 1;
cds.cbData = message.Length + 1;
cds.lpData = Marshal.StringToHGlobalAnsi(message);
IntPtr cdsBuffer = IntPtrAlloc(cds);
PostMessage(hWnd, WM_COPYDATA, IntPtr.Zero, cdsBuffer);
IntPtrFree(cds.lpData);
IntPtrFree(cdsBuffer);
}
}
}
}
my c++ app (main.exe):
int main(){
MSG message;
for(int i = 0; i < 1000; i++)
{
std::cout << "working" << std::endl;
Sleep(2 * 1000);
if(PeekMessage(&message, NULL, 0, 0, PM_NOREMOVE))
{
break;
}
}
int x;
cout<<"got it!";
cin>>x;
return 0;
}
when i start the c# program. no errors, no nothing.
same with c++, no errors, no nothing but never break the for loop :(
thanks for everyone for their time.

First of all, Process.Handle is the handle of the process instead of the window.
Secondly, since your main.exe is a console application and it only has a console window, you can only get the handle of the console window by using MainWindowHandle. However, the console does not belong to the main.exe, So you cannot use PeekMessage to handle the message sent to the console window. Console windows are owned by the console subsystem, csrss.exe(see https://stackoverflow.com/a/28248281/10611792). You should create your own window for your C++ app, or create a Message-Only window. Then, you can use FindWindow to get the window handle in C#:
public partial class Form1 : Form
{
[DllImport("user32.dll")]
static extern long SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);
[DllImport("user32.dll",CharSet = CharSet.Unicode)]
static extern IntPtr FindWindow(string classname, string windowname);
...
private void Form1_Load(object sender, EventArgs e)
{
...
Thread.Sleep(3000);
string message = "This is a test";
IntPtr hWnd = FindWindow("MyClass", "MyTitle");
if (hWnd == IntPtr.Zero)
{
MessageBox.Show("couldn't find the process");
}
else
{
COPYDATASTRUCT cds;
cds.dwData = 1;
cds.cbData = message.Length + 1;
cds.lpData = Marshal.StringToHGlobalAnsi(message);
IntPtr cdsBuffer = IntPtrAlloc(cds);
SendMessage(hWnd, WM_COPYDATA, IntPtr.Zero, cdsBuffer);
IntPtrFree(cds.lpData);
IntPtrFree(cdsBuffer);
}
}
}
C++:
LRESULT CALLBACK WindProc(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam)
{
if (Msg == WM_COPYDATA)
{
PCOPYDATASTRUCT data = (PCOPYDATASTRUCT)lParam;
MessageBoxA(hWnd, (LPSTR)data->lpData, "info", 0); // The character set depends on the characters you send
PostQuitMessage(0);
return 0;
}
return DefWindowProc(hWnd, Msg, wParam, lParam);
}
int main() {
WNDCLASSEX wcx = { 0 };
wcx.cbSize = sizeof(WNDCLASSEX);
wcx.lpfnWndProc = WindProc;
wcx.hInstance = GetModuleHandle(NULL);
wcx.lpszClassName = TEXT("MyClass");
RegisterClassEx(&wcx);
HWND hWnd = CreateWindowEx(0, TEXT("MyClass"), TEXT("MyTitle"), 0, 0, 0, 0, 0, HWND_MESSAGE, NULL, GetModuleHandle(NULL), NULL);
MSG msg;
for (int i = 0; i < 1000; i++)
{
std::cout << "working" << std::endl;
Sleep(2 * 1000);
if (PeekMessage(&msg, NULL, 0, 0, PM_NOREMOVE))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
break;
}
}
int x;
cout << "got it!";
cin >> x;
return 0;
}
Also Note that use SendMessage instead of PostMessage.
In addition, you can also choose other IPC methods.

Can't send WM_INPUTLANGCHANGEREQUEST to some controls

I'm working on (yet another) keyboard layout switcher and got strange troubles with Skype window (ver 6.22 on win7 x64). Any combinations of GetForegroundWindow() / GetFocus() / GetParentWindow() don't succeed to change the layout only inside the message input and, even more strange, only if more than one character is entered. Other cases work perfectly nice except wpf apps which refuse to obey without focusedHandle stuff.
public static void SetNextKeyboardLayout()
{
IntPtr hWnd = GetForegroundWindow();
uint processId;
uint activeThreadId = GetWindowThreadProcessId(hWnd, out processId);
uint currentThreadId = GetCurrentThreadId();
AttachThreadInput(activeThreadId, currentThreadId, true);
IntPtr focusedHandle = GetFocus();
AttachThreadInput(activeThreadId, currentThreadId, false);
PostMessage(focusedHandle == IntPtr.Zero ? hWnd : focusedHandle, WM_INPUTLANGCHANGEREQUEST, INPUTLANGCHANGE_FORWARD, HKL_NEXT);
}
I'm new to winapi things, so any help will be kindly appreciated, thank you.

After disassembling some of working products i've figured out that i was close to the right algorythm which looks like this:
public static void SetNextKeyboardLayout()
{
IntPtr hWnd = IntPtr.Zero;
var threadId = GetWindowThreadProcessId(GetForegroundWindow(), IntPtr.Zero);
var currentThreadId = GetCurrentThreadId();
var info = new GUITHREADINFO();
info.cbSize = Marshal.SizeOf(info);
var success = GetGUIThreadInfo(threadId, ref info);
// target = hwndCaret || hwndFocus || (AttachThreadInput + GetFocus) || hwndActive || GetForegroundWindow
AttachThreadInput(threadId, currentThreadId, true);
IntPtr focusedHandle = GetFocus();
AttachThreadInput(threadId, currentThreadId, false);
if (success)
{
if (info.hwndCaret != IntPtr.Zero) { hWnd = info.hwndCaret; }
else if (info.hwndFocus != IntPtr.Zero) { hWnd = info.hwndFocus; }
else if (focusedHandle != IntPtr.Zero) { hWnd = focusedHandle; }
else if (info.hwndActive != IntPtr.Zero) { hWnd = info.hwndActive; }
}
else
{
hWnd = focusedHandle;
}
if (hWnd == IntPtr.Zero) { hWnd = GetForegroundWindow(); }
PostMessage(hWnd, WM_INPUTLANGCHANGEREQUEST, INPUTLANGCHANGE_FORWARD, HKL_NEXT);
}
But the problem was not in finding PostMessage target hWnd, but in skype's input handling. I have solved it by adding a tiny delay before WM_INPUTLANGCHANGEREQUEST so skype can properly process all the input sent to it. Now i have to get things working without this delay but this is another story.

You should try this: PostMessage(hWnd,WM_INPUTLANGCHANGEREQUEST,0,(LPARAM)HKL_NEXT);
P.S.:
Under Windows 10 any WM_INPUTLANGCHANGEREQUEST crashes Skype.

Best way with Windows 10 -- is emulate keys for switch keyboard layout, like this:
keybd_event(VK_LWIN, 0, KEYEVENTF_EXTENDEDKEY, 0);
keybd_event(VK_SPACE,0, KEYEVENTF_EXTENDEDKEY, 0);
Sleep(10);
keybd_event(VK_SPACE,0, KEYEVENTF_EXTENDEDKEY | KEYEVENTF_KEYUP, 0);
keybd_event(VK_LWIN, 0, KEYEVENTF_EXTENDEDKEY | KEYEVENTF_KEYUP, 0);

C# Pinvoke can't find the Hwnd of Controls after List count was 0 at first time

I'm trying to click a Button in another Application (started from my Programm with Process.Start)
The problem: I need to wait until the Loading screen is disappeared and the GUI pop's up...
My idea was to read all (Hwnd)Controls until a specific Control (Button: "Kill Client") from the GUI was found (=GUI Opened).
But this only works if I wait manually for the GUI and press a "Search Control" button.
If I press the "Search Button" if the Loading Screen is aktive I get a Hwnd = 0 (List<'IntPtr> Count is also 0...) and if i press it again if the GUI is opened it is 0 again(List<'IntPtr> Count too...) !!!
Here my Code:
public class WndSearcher
{
[DllImport("user32")]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool EnumChildWindows(IntPtr window, EnumWindowProc callback, IntPtr i);
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;
}
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);
return true;
}
}
My Button:
List<IntPtr> AllControlHandles = WndSearcher.GetChildWindows(selectedCharacter.Botprocess.MainWindowHandle);
IntPtr ControlHandle = AllControlHandles.Find(x => PInvoke.GetWindowTextRaw(x) == "Kill Client" ? true : false);
MessageBox.Show(ControlHandle.ToString());
Part of PInvoke (Class):
const int WM_GETTEXT = 0x000D;
const int WM_GETTEXTLENGTH = 0x000E;
[DllImport("user32.dll", CharSet = CharSet.Auto)]
static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, IntPtr wParam, [Out] StringBuilder lParam);
public static string GetWindowTextRaw(IntPtr hwnd)
{
// Allocate correct string length first
int length = (int)SendMessage(hwnd, WM_GETTEXTLENGTH, IntPtr.Zero, null);
StringBuilder sb = new StringBuilder(length + 1);
SendMessage(hwnd, WM_GETTEXT, (IntPtr)sb.Capacity, sb);
return sb.ToString();
}

Found no solution till now.
So I decided to use AutoHotKey in combination with C#.
In C# I start my AutoHotKey Script and wait until the Script is finished. (Then the external Programm is started completely)
Starting Arguments: 1.Processid 2.NewExternalProgramName
Here my AutoHotKey Script:
counter := 0
Loop, %0% ; For each parameter:
{
param := %A_Index%
if (counter = 0) ; do sth with parameter 1
winwait, ahk_pid %param% ; Not logged in ;wait until the text "Not logged in" can be read (Program started completely)
if (counter = 1) ; do sth with parameter 2
WinSetTitle, %param%
counter += 1
}

Using User32.dll SendMessage to send string to another Windows Forms application

I have a strange problem.
I am using SendMessage to send a string to all running instances of the same Windows Forms application.
I can successfully send the string representation of the numeric value of an IntPtr pointer, like so:
unsafe private void SendString(IntPtr handle, IntPtr myHandle)
{
string s = handle.ToString(); // This will work and the value will be received.
// Try with "123553" which wont work.
// How can that be?
IntPtr lpData = Marshal.StringToHGlobalUni(s);
COPYDATASTRUCT data = new COPYDATASTRUCT();
data.dwData = 0;
data.cbData = s.Length * 2;
data.lpData = lpData;
IntPtr lpStruct = Marshal.AllocHGlobal(
Marshal.SizeOf(data));
Marshal.StructureToPtr(data, lpStruct, false);
int hTarget;
var succes = Int32.TryParse(s, out hTarget);
if (succes)
SendMessage(hTarget, WM_COPYDATA, handle, lpStruct);
}
The receiving application(s) correctly outputs a value like '123553'.
However, if I manually assign a value to s nothing is received:
string s = "123553";
Does anyone have an idea why calling ToString on an IntPtr and hardcoding the value doesn't produce the same behavior?
The code for running the application yourself is here:
public const int WM_COPYDATA = 0x004a;
[StructLayout(LayoutKind.Sequential)]
public struct COPYDATASTRUCT
{
[MarshalAs(UnmanagedType.I4)]
public int dwData;
[MarshalAs(UnmanagedType.I4)]
public int cbData;
[MarshalAs(UnmanagedType.SysInt)]
public IntPtr lpData;
}
[DllImport("User32.dll")]
private static extern bool SendMessage(int hWnd,
int wMsg, IntPtr wParam, IntPtr lParam);
public Form1()
{
InitializeComponent();
}
unsafe protected override void WndProc(ref Message message)
{
if (message.Msg == WM_COPYDATA)
{
COPYDATASTRUCT data = (COPYDATASTRUCT)
message.GetLParam(typeof(COPYDATASTRUCT));
string str = new string((char*)(data.lpData),
0, data.cbData / 2);
Debug.WriteLine(str);
}
base.WndProc(ref message);
}
unsafe private void SendString(IntPtr handle, IntPtr myHandle)
{
string s = handle.ToString();
IntPtr lpData = Marshal.StringToHGlobalUni(s);
COPYDATASTRUCT data = new COPYDATASTRUCT();
data.dwData = 0;
data.cbData = s.Length * 2;
data.lpData = lpData;
IntPtr lpStruct = Marshal.AllocHGlobal(
Marshal.SizeOf(data));
Marshal.StructureToPtr(data, lpStruct, false);
int hTarget;
var succes = Int32.TryParse(s, out hTarget);
if (succes)
SendMessage(hTarget, WM_COPYDATA, handle, lpStruct);
}
private void button1_Click(object sender, EventArgs e)
{
Process currentProcess = Process.GetCurrentProcess();
var handles = (from process in Process.GetProcesses()
where
process.Id != currentProcess.Id &&
process.ProcessName.Equals(
currentProcess.ProcessName,
StringComparison.Ordinal)
select process.MainWindowHandle).ToList<IntPtr>();
foreach (var handle in handles)
{
SendString(handle, this.Handle);
Debug.WriteLine(string.Format("Sending handle {0} from handle {1}", handle, this.Handle));
}
}
Sources:
Detecting if another instance of the application is already running
Using WM_COPYDATA for interprocess communication (VFP9)

DeviceIoControl can't eject a non-empty CDROM drive?

I tried using DeviceIoControl function (Win32 API function) to eject my CDROM drive, it works perfectly when my CDROM drive has no disk, but after inserting a disk in it, the Marshal.GetLastWin32Error() returned 32 (ERROR_SHARING_VIOLATION: The process cannot access the file because it is being used by another process), the driveHandle passed in the DeviceIoControl is created by CreateFile() function.
Could you please help me out? I like this way of manipulating the CD ROM related stuff, I can use winmm.dll to eject my CDROM but I think this way is worth to try.
OK, here is the code:
using System;
using System.ComponentModel;
using System.Text;
using System.Windows.Forms;
using System.IO;
using System.Runtime.InteropServices;
namespace DVD_ejector
{
public partial class Form1 : Form
{
const int OPENEXISTING = 3;
const int IOCTL_STORAGE_EJECT_MEDIA = 2967560;
const uint GENERICREAD = 0x80000000;
const int INVALID_HANDLE = -1;
public Form1()
{
InitializeComponent();
DriveInfo[] drs = DriveInfo.GetDrives();
List<DriveInfo> cdRoms = new List<DriveInfo>();
foreach (DriveInfo dInfo in drs)
{
if (dInfo.DriveType == DriveType.CDRom)
{
cdRoms.Add(dInfo);
}
}
comboBox1.DataSource = cdRoms;
comboBox1.DisplayMember = "Name";
if (comboBox1.Items.Count > 0) comboBox1.SelectedIndex = 0;
button1.Click += (sender, e) =>
{
Eject(#"\\.\" + ((DriveInfo)comboBox1.SelectedItem).Name[0]+":");
};
}
[DllImport("kernel32", SetLastError=true)]
static extern IntPtr CreateFile(string fileName, uint desiredAccess, uint shareMode, IntPtr attributes,uint creationDisposition, uint flagsAndAttribute, IntPtr fileTemplate);
[DllImport("kernel32")]
static extern int CloseHandle(IntPtr fileHandle);
[DllImport("kernel32")]
static extern bool DeviceIoControl(IntPtr driveHandle, int ctrlCode, IntPtr inBuffer, int inBufferSize, IntPtr outBuffer, int outBufferSize, ref int bytesReturned, IntPtr overlapped);
int bytesReturned;
private void Eject(string cdDrive)
{
IntPtr driveHandle = CreateFile(cdDrive, GENERICREAD, 0, IntPtr.Zero, OPENEXISTING, 0, IntPtr.Zero);
try
{
if((int)driveHandle != INVALID_HANDLE)
DeviceIoControl(driveHandle, IOCTL_STORAGE_EJECT_MEDIA, IntPtr.Zero, 0, IntPtr.Zero, 0, ref bytesReturned, IntPtr.Zero);
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
finally
{
CloseHandle(driveHandle);
}
}
}
}

As the error states, the device is being used by something else, but it's failing on the CreateFile call instead of the DeviceIoControl, and your code is not correctly checking for the failure.
The reason you're getting a sharing violation is because you're trying to open the device exclusively which will fail if ANYTHING has tried to open it or a file on it, including anti virus, Explorer, Search indexer, etc.
This updated Eject function fixes the share mode and the error handling and now reports the errors in the correct places.
private void Eject(string cdDrive) {
IntPtr driveHandle = new IntPtr(INVALID_HANDLE);
try {
// Open the device
driveHandle = CreateFile(cdDrive, GENERICREAD, FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, IntPtr.Zero, OPENEXISTING, 0, IntPtr.Zero);
if ((int)driveHandle == INVALID_HANDLE) { throw new Win32Exception(); }
// Try and eject
bool ejected = DeviceIoControl(driveHandle, IOCTL_STORAGE_EJECT_MEDIA, IntPtr.Zero, 0, IntPtr.Zero, 0, ref bytesReturned, IntPtr.Zero);
if (!ejected) { throw new Win32Exception(); }
} catch (Exception ex) {
MessageBox.Show(ex.Message);
} finally {
if ((int)driveHandle != INVALID_HANDLE) { CloseHandle(driveHandle); }
}
}