Window Handle and Process Handle

[Subramaniam s V]

Hi, What is the difference between a process handle and a window handle? Is there any convertions between the two? Thanks

[Stephen Hewitt]

A window handle (a HWND) identifies a window and a process handle (HANDLE) enables you to monitor/control a process. There is no direct meaningful conversion between them. That said writing code what enumerates all the windows handles in a given process is possible. It is also possible to go from a HWND to a HANDLE for the owning process as follows:

DWORD dwProcessID;
GetWindowThreadProcessId(hWnd, &dwProcessID);
HANDLE hProcessHandle = OpenProcess(PROCESS_ALL_ACCESS, FALSE, dwProcessID);

Steve

[Monty2]

HWND is a Handle to a Window Where as process handle is a handle to a process (Note: a process may or maynot have a window) So Both are different things, the correct question will be how can i get the process id if i have the HWND of one of its windows GetWindowThreadProcessId gives the process id to get the opposite (processid to window handle) you have to enumerate all the windows and compare the process id.

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C makes it easy to shoot yourself in the foot; C++ makes it harder, but when you do, it blows away your whole leg

[Subramaniam s V]

Yeah. I do accept that a window handle is a handle to a window and a process handle is a handle to a process and not all the time a process can have a window. But, Internet Explorer has a window by default. If I am gonna launch IE from my application as a process I get the process handle for IE. At this point of time, will I be able to get the window handle of the new IE process launched or is there any methods that converts my process ID got(from createprocess functions) to a window handle.

[Monty2]

any methods that converts my process ID got(from createprocess functions) to a window handle. First of all don't use *convert*, second open Spy++ and open up IE then you will see that IE has lots windows, not just one window (toolbars,menus ...) so the question is which window's handle you want what do you want to do anyway ?

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C makes it easy to shoot yourself in the foot; C++ makes it harder, but when you do, it blows away your whole leg

[Stephen Hewitt]

As Monty v2.0 said, a mapping from a process to a HWND is a one to many mapping. Here's how you would go about doing it however:

// Add this function.
BOOL CALLBACK EnumWindowsProc(HWND hwnd, LPARAM lParam)
{
     DWORD dwProcessID;
     GetWindowThreadProcessId(hwnd, &dwProcessID)
     if ( dwProcessID == lParam )
     {
         // "hwnd" is a top level window belonging to the process.
     {
 
     return TRUE;
}
 
// Add this code directly after calling CreateProcess. pi is the PROCESS_INFORMATION struct.
CloseHandle(pi.hThread);
WaitForInputIdle(pi.hProcess, INFINITE); // Wait for for IE...
CloseHandle(pi.hProcess);
EnumWindows(&EnumWindowsProc, pi.dwProcessId);

I have not actually tested this code but the idea is sound. Now that I've given this example here's some advice - DON'T USE IT (unless you have no choice)! You should look into controlling IE through OLE Automation. Steve