Determining the bitness of an IntPtr instance using EnumChildWindows

I posted a similar question here but decided to re-post focusing on part of the question.

I am enumerating windows using EnumWindows and EnumChildWindows on a 64 bit Windows 7 from a 32 bit WinForms application. Here is the declaration:

public delegate int EnumWindowsCallback (System.IntPtr hWnd, System.IntPtr lParam);

[DllImport("user32.Dll")]
public static extern bool EnumWindows (EnumWindowsCallback lpEnumCallbackFunc, IntPtr lParam);

[DllImport("user32")]
public static extern bool EnumChildWindows (IntPtr hWnd, EnumWindowsCallback lpEnumCallbackFunc, IntPtr lParam);

I send [Process.GetProcesses()[i].MainWindowHandle] as a parameter to [EnumWindows] to enumerate all child windows of all processes.

When [EnumChildWindows] is called, the [hWnd] parameter could be a handle to a window running in a 32 or 64 bit process. Since my app is 32 bit, how can I tell whether to call [hWnd.ToInt32()] or [hWnd.ToInt64()]. I need to call one of the two functions to compare one IntPtr to another.

Context: Windows 7 (64 bit), VS 2010, WinForms (32 bit).

Solution

You should not need to do anything special, a hwnd is not a pointer its a HANDLE and for this type 64 bit Windows guarantees that only the lower 32 bits are significant so they can be freely shared.