Getting an HWND from an HINSTANCE

[Chris Richardson]

GetWindowThreadProcessId will give you the process ID/thread ID of the process/thread that created the window handle. Chris Richardson

[Harold Bamford]

Chris, Well, I tried enumerating all the windows and using GetWindowThreadProcessId() and it doesn't seem to give me the same process id as obtained from the SHELLEXECUTEINFO structure (updated by ShellExecuteEx()): The enumeration callback:

class WININFO
{
public:
	CWnd *hWnd;
	HINSTANCE hInst;
	CString title;
	WININFO(CWnd *wnd = NULL, HINSTANCE inst = NULL) {hWnd = wnd; hInst = inst; title = "";}
};
typedef CArray<WININFO,WININFO> CArrayWinInfo;

BOOL CALLBACK CIOGuidesView::enumwndfn(HWND hWnd, LPARAM lParam)
{
	CIOGuidesView *me = (CIOGuidesView *)lParam;
	return me->enumwndfn(CWnd::FromHandle(hWnd));
}

BOOL CIOGuidesView::enumwndfn(CWnd * wnd)
{
	WININFO wininfo(wnd);

	wnd->GetWindowText(wininfo.title);

	DWORD ProcessId; 
	GetWindowThreadProcessId (wnd->GetSafeHwnd(), &ProcessId ); 
	wininfo.hInst = (HINSTANCE)ProcessId;

	m_WinInfoArray.Add(wininfo);

	return TRUE;
}

The ShellExecuteEx() call:

void CIOGuidesView::OnButton1() 
{
	CString filename("PDF Files\\751018a.pdf");

	HANDLE hProcess = NULL;
	SHELLEXECUTEINFO shellInfo;
	::ZeroMemory(&shellInfo, sizeof(shellInfo));
	shellInfo.cbSize = sizeof(shellInfo);
	shellInfo.lpVerb = "open";
	shellInfo.lpFile = filename;
	shellInfo.fMask = SEE_MASK_NOCLOSEPROCESS;
	if(::ShellExecuteEx(&shellInfo))
	{ /* success */
		hProcess = shellInfo.hProcess;
	} /* success */
	else
	{
		ShowLastError("ShellExecuteEx Failed");
		return;
	}


	int reason = WaitForInputIdle(hProcess,INFINITE);
	// blah, blah

And then I dumped all the windows whose title began with "Acro" OR those whose hInst matched my hProcess:

	hProcess=0x01D8  hInst=0x045C  title='Acrobat Reader'

If I understand this, the hProcess and hInst values should have been identical. Ideas?

[Chris Richardson]

The HINSTANCE is not the same as the ID of the process. What you need to do, is use the ID of the process to get a handle to the process, which can be compared directly to the hProcess member of SHELLEXECUTEEX. Something like this:

BOOL CIOGuidesView::enumwndfn(CWnd * wnd)
{
WININFO wininfo(wnd);

wnd->GetWindowText(wininfo.title);

DWORD ProcessId;
GetWindowThreadProcessId (wnd->GetSafeHwnd(), &ProcessId );
// We open a handle to the process, which can be compared with the handle returned by ShellExecuteEx.
// Sometime in the future, we must call CloseHandle with the handle returned by OpenProcess...
HANDLE a_hProcess = OpenProcess( PROCESS_QUERY_INFORMATION, FALSE, ProcessID );
wininfo.hInst = (HINSTANCE)a_hProcess;

m_WinInfoArray.Add(wininfo);

return TRUE;
}

Chris Richardson

[Phil J Pearson]

Chris Richardson wrote: // We open a handle to the process, which can be compared with the handle returned by ShellExecuteEx. // Sometime in the future, we must call CloseHandle with the handle returned by OpenProcess... Why not close it immediately? Once you got the handle all you need it its value to use for comparison, you don't need to do anything else with it.

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[Chris Richardson]

Whoops. I guess I had a momentary lapse of brain activity :zzz:. Chris Richardson

[Harold Bamford]

Chris, I suspected I was mixing apples and oranges. But it still doesn't seem to work.

BOOL CIOGuidesView::enumwndfn(CWnd * wnd)
{
	WININFO wininfo(wnd);
		

	wnd->GetWindowText(wininfo.title);
		

	DWORD ProcessId; 
	GetWindowThreadProcessId (wnd->GetSafeHwnd(), &ProcessId ); 
		

	// We open a handle to the process, which can be compared with the handle
	// returned by ShellExecuteEx.
	HANDLE a_hProcess = OpenProcess( PROCESS_QUERY_INFORMATION, FALSE, ProcessId );
	wininfo.hInst = (HINSTANCE)a_hProcess;
	CloseHandle(a_hProcess);  // only need it for comparison purposes
		
	//wininfo.hInst = (HINSTANCE)ProcessId;  // the wrong way...

	m_WinInfoArray.Add(wininfo);

	return TRUE;
}

This still yields no exact matches on hProcess (from ShellExecuteEx) and a_hProcess (from OpenProcess). I am beginning to wonder if AcroRd32.exe does something especially weird. I'll try something with another type of file... I appreciate you looking at this. It has me bamboozled!

[Chris Richardson]

It seems that on my machine, OpenProcess is always returning the same value, no matter which ID you give it. That's pretty strange, but there's another way to do this. You could use CreateProcess, instead of ShellExecuteEx. CreateProcess will give you the ID of the process as well as it's handle, so you could directly compare the process ID gotten from GetWindowThreadProcessId with the process ID returned in the PROCESS_INFORMATION struct (from CreateProcess). I'll mess with this approach for a little while longer, and if I can get it to work, I'll let you know. Chris Richardson

[Harold Bamford]

Chris, I was just about to post a message here saying pretty much the same thing: OpenProcess() is giving the same value for different windows. I checked that they were truly different processes via the Task Manager. I was hoping to avoid CreateProcess() as I like the idea of ShellExecuteEx()'s looking up the default program based on the file type. So I just use an lpVerb of "open" and the lpFile points to the .pdf file and ShellExecuteEx() takes care of everything else. I suppose I can write the code to search the registry and duplicate this but it doesn't sound fun. :(( I don't suppose CreateProcess() does this kind of thing, does it?

[Chris Richardson]

CreateProcess won't do it for you, but you can use a function called SHGetFileInfo to get the exe path for you. Take a look at the SHGFI_ICONLOCATION flag of that function. It will get you the path to the .exe file containing the icon for the passed in .pdf file. Almost assuredly Acrobat Reader stores it's icon inside it's exe file, but this could be verified. If this sounds a little hackish and risky, then the registry stuff isn't all that bad anyways. Good luck with it, Chris Richardson

[JT Anderson]

You might find the FindExecutable function useful.

[Harold Bamford]

OK, thanks to all you folks giving me help, I think I have it. I now use FindExecutable() to get the default program, then CreateProcess() to spawn it:

	// Get the name of the program that runs on a .pdf file
	char *filename = "C:\\src\\IOGuides\\PDF Files\\751018a.pdf";
	TCHAR szExe[MAX_PATH];
	::FindExecutable(filename, _T(""), szExe);
 
	HANDLE hProcess = NULL;	// Use for WaitForInputIdle()
	STARTUPINFO startupInfo;
	PROCESS_INFORMATION processInfo;
	::ZeroMemory(&startupInfo, sizeof(startupInfo));
	startupInfo.cb = sizeof(startupInfo);
	::ZeroMemory(&processInfo, sizeof(processInfo));  // better safe than sorry
 
	char cmd[MAX_PATH + MAX_PATH + 5];
	sprintf(cmd,"\"%s\" \"%s\"", szExe, filename);
	BOOL startedOK = CreateProcess(
		NULL,
		cmd,	// "acrord32.exe file.pdf"
		NULL,	// Process security
		NULL,	// Thread security
		FALSE,	// Inheritance
		0,	// no special startup flags
		NULL,	// no special environment
		NULL,	// no default startup directory
		&startupInfo,
		&processInfo);
 
	if(!startedOK)
	{
		ShowLastError(filename);
		return;
	}
 
	hProcess = processInfo.hProcess; 
	WaitForInputIdle(hProcess,INFINITE);

I then get the process ID from processInfo.dwProcessId and enumerate all the windows, using GetWindowThreadProcessId() to get the associated process ID.

BOOL CIOGuidesView::enumwndfn(CWnd * wnd)
{
	WININFO wininfo(wnd);
 
	wnd->GetWindowText(wininfo.title);
 
	DWORD ProcessId; 
	GetWindowThreadProcessId (wnd->GetSafeHwnd(), &ProcessId ); 
	wininfo.Pid = ProcessId;
 
	m_WinInfoArray.Add(wininfo);
 
	return TRUE;
}

Comparing processInfo.dwProcessId against the value from GetWindowThreadProcessId() gives me the match-up I needed. Unfortunately, AcroRd32.exe is cutesy and allows only one instance to run at a time. If I already have the Reader running, the new process just closes down. Presumably after talking to its counterpart and giving the new filename. Sigh. I guess I can kill the old one first, but that won't alway work if the user manually started up AcroRd32. Thanks for all your help. I'll probably make a "beginner" level article showing all of this in the next few weeks since doing this is not so obvious. I suspect the trick in making the article will be coming up with keywords and phrases to allow people to find it when they are looking to do this kind of thing. All the information I needed was in the articles; I just couldn't find it. Again, many thanks for all of your