Re: Doing the Right Thing with IPersistStream

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.atl

Date:

Fri, 3 Nov 2006 13:52:36 -0500

Message-ID:

<#SsJ8k3$GHA.4428@TK2MSFTNGP04.phx.gbl>

Jason S <jmsachs@gmail.com> wrote:

Didn't you say that you already have your file format defined?
Shouldn't you follow that format then?

I said it's a custom format. I have the ability to tweak it, since I'm
the one writing the tools/interface utilities to use it.

You must be able to read back exactly as many bytes as you've originally
written. COM doesn't care if that's achieved with a length prefix, a
special terminator, or in any other way.

A thought just occurred to me which makes me uneasy... I assume that
if my object is implementing IPersistStream, that I can't assume it's
the only object contained in the file. is that correct?

In general, yes. That's why you must read exactly the same number of
bytes you've written - somebody else's data might be in the stream right
after yours.

It sounds like IPersistFile may be more suitable persistence mechanism
for your application.
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925