C# Signature:

[DllImport("kernel32.dll")]
static extern uint GetLastError();
// GetLastError is save!

Tested extensively here http://stackoverflow.com/questions/17918266/winapi-getlasterror-vs-marshal-getlastwin32error

// You should never PInvoke to GetLastError.  Call Marshal.GetLastWin32Error instead!

VB Signature:

' You should never PInvoke to GetLastError.  Call Marshal.GetLastWin32Error instead!

Boo Signature:

[DllImport("kernel32.dll")]
def GetLastError() as int:
     pass

Notes:

Calling GetLastError directly via PInvoke is not guaranteed to work due to the CLR's internal interaction with the operating system. Instead, call Marshal.GetLastWin32Error.

Don't forget to include [SetLastError = true] in your function definition. For example:

    [DllImport("kernel32.dll", SetLastError = true)]
    static extern bool CloseHandle(IntPtr hObject);

To retrieve the error message corresponding to this error code, you can use the Win32Exception class, as explained in the FormatMessage page (look at the bottom of the page).

Alternative Managed API:

System.Runtime.InteropServices.Marshal.GetLastWin32Error

Call GetLastWin32Error immediately after the Win32 API call or the result is unpredictable. See MSDN:

http://msdn.microsoft.com/en-us/library/ms182199(v=vs.80).aspx