How can I detect if my process is running UAC-elevated or not?

For those of us working in C#, in the Windows SDK there is a "UACDemo" application as a part of the "Cross Technology Samples". They find if the current user is an administrator using this method:

private bool IsAdministrator
{
    get
    {
        WindowsIdentity wi = WindowsIdentity.GetCurrent();
        WindowsPrincipal wp = new WindowsPrincipal(wi);

        return wp.IsInRole(WindowsBuiltInRole.Administrator);
    }
}

(Note: I refactored the original code to be a property, rather than an "if" statement)

The following C++ function can do that:

HRESULT GetElevationType( __out TOKEN_ELEVATION_TYPE * ptet );

/*
Parameters:

ptet
    [out] Pointer to a variable that receives the elevation type of the current process.

    The possible values are:

    TokenElevationTypeDefault - This value indicates that either UAC is disabled, 
        or the process is started by a standard user (not a member of the Administrators group).

    The following two values can be returned only if both the UAC is enabled
    and the user is a member of the Administrator's group:

    TokenElevationTypeFull - the process is running elevated. 

    TokenElevationTypeLimited - the process is not running elevated.

Return Values:

    If the function succeeds, the return value is S_OK. 
    If the function fails, the return value is E_FAIL. To get extended error information, call GetLastError().

Implementation:
*/

HRESULT GetElevationType( __out TOKEN_ELEVATION_TYPE * ptet )
{
    if ( !IsVista() )
        return E_FAIL;

    HRESULT hResult = E_FAIL; // assume an error occurred
    HANDLE hToken   = NULL;

    if ( !::OpenProcessToken( 
                ::GetCurrentProcess(), 
                TOKEN_QUERY, 
                &hToken ) )
    {
        return hResult;
    }

    DWORD dwReturnLength = 0;

    if ( ::GetTokenInformation(
                hToken,
                TokenElevationType,
                ptet,
                sizeof( *ptet ),
                &dwReturnLength ) )
    {
            ASSERT( dwReturnLength == sizeof( *ptet ) );
            hResult = S_OK;
    }

    ::CloseHandle( hToken );

    return hResult;
}