How to Get the Main Window Handle from a Process ID in C ?

How to Retrieve the Main Window Handle from a Process ID

Question:

How can you retrieve the main window handle from a given process ID? You want to bring this particular window to the forefront, and Process Explorer seems to perform this action seamlessly.

Answer:

Investigating the mechanism used by .NET to determine the main window revealed that it employs the EnumWindows() function. The following C code provides a similar implementation:

struct handle_data {
    unsigned long process_id;
    HWND window_handle;
};

HWND find_main_window(unsigned long process_id) {
    handle_data data;
    data.process_id = process_id;
    data.window_handle = 0;
    EnumWindows(enum_windows_callback, (LPARAM)&data);
    return data.window_handle;
}

BOOL CALLBACK enum_windows_callback(HWND handle, LPARAM lParam) {
    handle_data& data = *(handle_data*)lParam;
    unsigned long process_id = 0;
    GetWindowThreadProcessId(handle, &process_id);
    if (data.process_id != process_id || !is_main_window(handle))
        return TRUE;
    data.window_handle = handle;
    return FALSE;   
}

BOOL is_main_window(HWND handle) {   
    return GetWindow(handle, GW_OWNER) == (HWND)0 && IsWindowVisible(handle);
}

This code iterates through all top-level windows and checks if the process ID of the window matches the desired process ID. If it does, it further verifies if the window is a main window (has no owner and is visible) and returns its handle.

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