How to find a window without (!!) using FindWindow() ?

[david112]

Hi everyone ,

I'm trying to close a window (in C++). I need to do that without the use of FindWindow().
My app should find a window of another app (again , without FindWindow()) and close it .

I've written both apps (two different apps , not in the same .cpp file) , one for the window , and one for the app that needs to find the window (not all done of course) , but I can't seem to find a way to find the window without "FindWindow".

any idea ?
thanks in advance
davi

[webJose]

Interprocess communication. Basically have the owner of the window transmit to the other application the window handle, or better yet: Have the application that wants to close the window transmit a command to the other application so it can close its own window.

Personally, I think I would use RegisterWindowMessage() to settle on the message to send, then whenever needed, the closer app would broadcast the message and in response, the owner app would close the window.

[andywestken]

Are your apps collaborative?

[Duthomhas]

That's a really strange requirement... Why can't you just use FindWindow()?

[naderST]

You can hook the mouse and when he click the window you can check if that's the window you want to close and then SendMessage.

[david112]

To webJose :

My friend , I don't understand how do I use the function "RegisterWindowMessage" in order to locate the windows that I want to close .

I'll give you the code that does it using FindWindow:

The following code is inside to application that wants to close the other application :

           HWND pHwnd;
            pHwnd = FindWindow("TestWin",NULL);
            SendMessage(pHwnd,WM_CLOSE,0,0);

The application that I want to close called "TestWin" .
Can you please explain to me how to do that without "pHwnd = FindWindow("TestWin",NULL);"


to andywestken : is they are, one way collaborative. The app that wants to close the other app , knows its name ,which is "TestWin" .

to naderST : can you please explain a little more ?

thanks a lot ,everyone

[Duthomhas]

I'm not so sure you are legit.

You are willing to use all kinds of Win API functions in odd ways to find a window, but you are unwilling to use the Win API function designed to do exactly that?

Something smells un-kosher here.

[webJose]

Since my approach needs to have the source code for both apps, I don't mind. True that not using FindWindow() is just a major pain, but to each its own, I guess.

With my approach, you need to change both apps. The app creating TestWin needs to register a window message when it starts up, say in WinMain:

//Globals
const TCHAR c_WindowMessageName = TEXT("MyWindowMessage"); //Or whatever name you like.
UINT closeMsg;

....
//Inside WinMain()....
closeMsg = RegisterWindowMessage(c_WindowMessageName);

Now, inside your TestWin's window procedure, you process this message. For this to work, the TestWin window must be a top level window:

case closeMsg:
    SendMessage(hWnd, WM_CLOSE, 0, 0);
    break;

Now the closer application just needs to register the same window message and you are good to go:

//Globals
const TCHAR c_WindowMessageName = TEXT("MyWindowMessage");
UINT closeMsg;

....
//Inside WinMain()....
closeMsg = RegisterWindowMessage(c_WindowMessageName);

....
//Send the close message whenever you want/need.  You must broadcast it.
//PostMessage so the call is non-blocking.
PostMessage(HWND_BROADCAST, closeMsg, 0, NULL);

[modoran]

Please note that internally FindWindow() will send WM_GETTEXT message to every top-level window, and if one of them is hunging, your application will hung too. So please use it carefully.

[andywestken]

modoran - do you have a reference for that? (re. FindWindow() sending WM_GETTEXT message)

Andy

[Kiana]

reiterating what Duoas has already said, what you're doing doesn't really make sense.

that said, EnumWindows will work fine for you

#include <windows.h>

typedef struct _PASS_AROUND {
  HWND* lphWnd;
  LPCTSTR lpcszClass;
} PASS_AROUND, *PPASS_AROUND;

BOOL CALLBACK FakeFindWindowCallback(__in HWND hWnd, __in LPARAM lParam)
{
  /***/ LPTSTR        lpszClass = new TCHAR[MAX_CLASS + 1];
  /***/ PPASS_AROUND  pParameter = reinterpret_cast<PPASS_AROUND>(lParam);
  const int           MAX_CLASS = 6969; // big number.. lol
  
  // able to get class name?
  if (GetClassName(hWnd, lpszClass, MAX_CLASS + 1) == 0)
    return TRUE; // continue
  
  // class name match?
  if (lstrcmp(lpszClass, pParameter->lpcszClass) != 0)
    return TRUE; // continue
    
  pParameter->lphWnd[0] = hWnd;
  return FALSE; // break
}

HWND FakeFindWindow(__in_z LPCTSTR lpcszClass = NULL)
{
  HWND hWnd = NULL;
  
  PASS_AROUND Parameter;
  Parameter.lphWnd      = &hWnd;
  Parameter.lpcszClass  = lpcszClass;
  
  EnumWindows(FakeFindWindowCallback, reinterpret_cast<LPARAM>(&Parameter));
  return hWnd;    
}

code largely untested & mostly likely won't compile, but you get the idea

[Duthomhas]

Please note that internally FindWindow() will send WM_GETTEXT message to every top-level window, and if one of them is hunging, your application will hung too. So please use it carefully.

What?!!

You're telling us that the OS doesn't have a list of top level windows it can look through?
That the people at MS that designed the system were so clueless that they implemented a heavily-utilized function in such a clumsy and easy to break way?

[edit] Please, keep the FUD down.

[david112]

Thanks everybody . The code works fine .

webJose , after the second application has closed , how can the first application know that the second application has just been closed ?
One way that works for me is by checking before everything , that the Process-ID of the second application is legit (i.e. not ZERO) , and it works fine , however the code for checking the P_id is a little bit large . Can I know in some other way if the second app closed itself ?

everybody,really , thanks a lot (you're indeed the bests)

[webJose]

I provided a one-way interprocess communication method. Now you want a two-way. For this it would be better if you used something else, like a named pipe. Google for them as I won't explain there here because they are not the most trivial, nor will I write the code for you. If you don't like them, then look up for other forms of interprocess communcation and pick up the one you like best.