Question

I know the HRESULT_FROM_WIN32 macro to convert a Win32 error code into an HRESULT, is there any way to do the conversion starting from an errno error?

Answer 1

In short, no.

As of http://msdn.microsoft.com/en-us/library/5814770t%28v=vs.100%29.aspx

The errno values are constants assigned to errno in the event of
various error conditions.

ERRNO.H contains the definitions of the errno values. However, not all
the definitions given in ERRNO.H are used in 32-bit Windows operating
systems. Some of the values in ERRNO.H are present to maintain
compatibility with the UNIX family of operating systems.

The errno values in a 32-bit Windows operating system are a subset of
the values for errno in XENIX systems. Thus, the errno value is not
necessarily the same as the actual error code returned by a system
call from the Windows operating systems. To access the actual
operating system error code, use the _doserrno variable, which
contains this value.

Of course you can write your own function with switch-cases which will “translate” error codes.

You can see that there are about 80 errno values defined on windows.