Marshal.GetLastWin32Error Method

Definition

Namespace:

System.Runtime.InteropServices

Assembly:

System.Runtime.InteropServices.dll

Source:

Marshal.cs

Returns the error code returned by the last unmanaged function that was called using platform invoke that has the SetLastError flag set.

public:
 static int GetLastWin32Error();

public static int GetLastWin32Error ();

static member GetLastWin32Error : unit -> int

Public Shared Function GetLastWin32Error () As Integer

Returns

Int32

The last error code set by a call to the Win32 SetLastError function.

Examples

The following example calls the GetLastWin32Error method. The example first demonstrates calling the method with no error present and then demonstrates calling the method with an error present.

using System;
using System.Runtime.InteropServices;

internal class Win32
{
    // Use DllImportAttribute to inport the Win32 MessageBox
    // function.  Set the SetLastError flag to true to allow
    // the function to set the Win32 error.
    [DllImportAttribute("user32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
    public static extern int MessageBox(IntPtr hwnd, String text, String caption, uint type);
}

class Program
{

    static void Run()
    {
        // Call the MessageBox with normal parameters.

        Console.WriteLine("Calling Win32 MessageBox without error...");

        Win32.MessageBox(new IntPtr(0), "Press OK...", "Press OK Dialog", 0);

        // Get the last error and display it.
        int error = Marshal.GetLastWin32Error();

        Console.WriteLine("The last Win32 Error was: " + error);

        // Call the MessageBox with an invalid window handle to
        // produce a Win32 error.

        Console.WriteLine("Calling Win32 MessageBox with error...");

        Win32.MessageBox(new IntPtr(123132), "Press OK...", "Press OK Dialog", 0);

        // Get the last error and display it.

        error = Marshal.GetLastWin32Error();

        Console.WriteLine("The last Win32 Error was: " + error);
    }

    static void Main(string[] args)
    {
        Run();
    }
}
// This code example displays the following to the console:
//
// Calling Win32 MessageBox without error...
// The last Win32 Error was: 0
// Calling Win32 MessageBox with error...
// The last Win32 Error was: 1400

Imports System.Runtime.InteropServices

Module Win32
    ' Use DllImportAttribute to inport the Win32 MessageBox
    ' function.  Set the SetLastError flag to true to allow
    ' the function to set the Win32 error.
    <DllImportAttribute("user32.dll", SetLastError:=True, CharSet:=CharSet.Unicode)> _
    Function MessageBox(ByVal hwnd As IntPtr, ByVal text As String, ByVal caption As String, ByVal type As UInt32) As Integer
    End Function

End Module

Module Program


    Sub Run()


        ' Call the MessageBox with normal parameters.

        Console.WriteLine("Calling Win32 MessageBox without error...")

        Win32.MessageBox(New IntPtr(0), "Press OK...", "Press OK Dialog", 0)

        ' Get the last error and display it.
        Dim errorVal As Integer

        errorVal = Marshal.GetLastWin32Error()

        Console.WriteLine("The last Win32 Error was: " + errorVal)

        ' Call the MessageBox with an invalid window handle to
        ' produce a Win32 error.

        Console.WriteLine("Calling Win32 MessageBox with error...")

        Win32.MessageBox(New IntPtr(123132), "Press OK...", "Press OK Dialog", 0)

        ' Get the last error and display it.

        errorVal = Marshal.GetLastWin32Error()

        Console.WriteLine("The last Win32 Error was: " + errorVal)

    End Sub

    Sub Main(ByVal args() As String)

        Run()

    End Sub

End Module

' This code example displays the following to the console: 
'
' Calling Win32 MessageBox without error...
' The last Win32 Error was: 0
' Calling Win32 MessageBox with error...
' The last Win32 Error was: 1400

Remarks

On Windows systems, GetLastWin32Error exposes the Win32 GetLastError function from Kernel32.DLL. This method exists because it is not reliable to make a direct platform invoke call to GetLastError to obtain this information. If you want to access this error code, you must call GetLastWin32Error instead of writing your own platform invoke definition for GetLastError and calling it. The common language runtime can make internal calls to APIs that overwrite the GetLastError maintained by the operating system.

You can use this method to obtain error codes only if you apply the System.Runtime.InteropServices.DllImportAttribute to the method signature and set the DllImportAttribute.SetLastError field to true. The process for this varies depending upon the source language used: C# and C++ are false by default, but the Declare statement in Visual Basic is true.

There is a difference in the behavior of the GetLastWin32Error method on .NET Core and .NET Framework when DllImportAttribute.SetLastError is true. On .NET Framework, the GetLastWin32Error method can retain error information from one P/Invoke call to the next. On .NET Core, error information is cleared before P/Invoke call, and the GetLastWin32Error represents only error information from the last method call.

On .NET 6 and later versions, this method is functionally equivalent to GetLastPInvokeError, which is named to better reflect the intent of the API and its cross-platform nature. GetLastPInvokeError should be preferred over GetLastWin32Error.

See also

• DllImportAttribute