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Question Marshal::GetLastWin32Error have unpredictable result

Discussion in 'Windows' started by Ruonan, Feb 8, 2023.

  1. Ruonan

    Ruonan

    Joined:
    Dec 6, 2012
    Posts:
    53
    Hey guys, I am working on a windows app build with unity3d. I try to pinvoke some user32.dll function and try to call Marshal::GetLastWin32Error() to get error code if there is any.


    I followed the guide line in those two pages: call Marshal::GetLastWin32Errorcall() instead of kernal32.dll's GetLastError and call it immediately after a user32 function call.

    Marshal.GetLastWin32Error Method (System.Runtime.InteropServices) | Microsoft Learn
    GetLastError function (errhandlingapi.h) - Win32 apps | Microsoft Learn

    My app worked just fine until I add Marshal::GetLastWin32Error call. Marshal::GetLastWin32Error just get some random errors.

    Can any help me with this problem? I am really confused .
    Thanks.
     
    Last edited: Feb 9, 2023
    Ruonan, Feb 8, 2023
    #1

  2. Tautvydas-Zilys

    Tautvydas-Zilys

    Unity Technologies

    Joined:
    Jul 25, 2013
    Posts:
    10,446
    Tautvydas-Zilys, Feb 8, 2023
    #2

  3. Ruonan

    Ruonan

    Joined:
    Dec 6, 2012
    Posts:
    53
    Oops it is typo, I am actully call Marshal.GetLastWin32Error();

    This is how I define those function.
    Code (CSharp):
    1.  
    2. [DllImport("user32.dll", SetLastError = true)]
    3. public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);
    and my function is like:
    Code (CSharp):
    1. var progman = User32.FindWindow(PROGMAN, null);
    2. var errorCode = Marshal.GetLastWin32Error();
    3. if (errorCode != 0)
    4.        UnityEngine.Debug.LogException(new Win32Exception(errorCode));
    Counld that be the error code from other program? I don't know if this function is multi-thread safe.
     
    Ruonan, Feb 9, 2023
    #3

  4. Tautvydas-Zilys

    Tautvydas-Zilys

    Unity Technologies

    Joined:
    Jul 25, 2013
    Posts:
    10,446
    No, it's stored in a thread local variable. However, I see an error in your usage of FindWindow: you are only supposed to call GetLastWin32Error() if FindWindow function fails. It will not set the error if it succeeds, so you might be seeing an error from a previous call to something else. Try this:

    Code (csharp):
    1. var progman = User32.FindWindow(PROGMAN, null);
    2. if (progman == IntPtr.Zero)
    3.     UnityEngine.Debug.LogException(new Win32Exception(Marshal.GetLastWin32Error()));
     
    Tautvydas-Zilys, Feb 9, 2023
    #4

  5. Ruonan

    Ruonan

    Joined:
    Dec 6, 2012
    Posts:
    53

    Oh, Thanks! I will try this one. Get back to this if it works.
     
    Ruonan, Feb 13, 2023
    #5