How to fetch the message string from Win32 provided HRESULT C#

Question

I'm curious if there is a function in C# to convert an Win32 HRESULT (long) error code gotten from unmanaged code into the representation string.

Answer 1

I’m not aware of a single function but the workaround is easy enough.

public static string formatMessage( int hr ) =>
    Marshal.GetExceptionForHR( hr ).Message;

Update: the “duplicate” question is very different.

HRESULT codes are documented in section 2.1 of the [MS-ERREF] spec.

Any Win32 code can be packed into HRESULT, by using Severity=1 and Facility=FACILITY_WIN32. The opposite is not true, FACILITY_WIN32 is just one of the many. The accepted answer to the “duplicate” question, which uses Win32Exception, doesn’t apply to this question.

Here's a quick demo.

static void testHresultMessages()
{
    int hr = new OverflowException().HResult;

    // Prints "Unknown error (0x80131516)"
    Console.WriteLine( new Win32Exception( hr ).Message );

    // Prints "Arithmetic operation resulted in an overflow."
    Console.WriteLine( Marshal.GetExceptionForHR( hr ).Message );
}