User32.GetWindowLongAuto throws an exception if result is 0

[vlad2048]

Describe the bug and how to reproduce

0 is a valid return value for GetWindowLong & GetWindowLongPtr. So it cannot be used alone to detect an error.

For example querying the extended styles (WindowStylesEx) of a window can return 0 as a valid value.

What code is involved

// PInvoke\User32\WinUser.Gdi.cs
public static IntPtr GetWindowLongAuto(HWND hWnd, WindowLongFlags nIndex)

Expected behavior Instead of just checking the return value against 0, we should:

• clear the last error Kernel32.SetLastError(0);
• query the function
• if the result is 0 and Kernel32.GetLastError returns an error then throw the Win32Exception

Screenshots n/a

[dahall]

I have updated the function as follows:

public static IntPtr GetWindowLongAuto(HWND hWnd, WindowLongFlags nIndex)
{
    SetLastErrorEx(0, 0);
    IntPtr ret = IntPtr.Size == 4 ? GetWindowLong(hWnd, nIndex) : GetWindowLongPtr(hWnd, nIndex);
    if (ret == IntPtr.Zero)
        Win32Error.GetLastError().ThrowIfFailed();
    return ret;
}