Re: [Boost-users] [iostreams] Closing a filtering_ostream

From: Jonathan Turkanis (technews_at_[hidden])
Date: 2005-10-06 19:40:59

Sorry I didn't reply sooner -- I've been away for the last few days.

Paul Giaccone wrote:
> How do you close a filtering_ostream object once you have finished
> writing to it?

You can use either pop() or reset().

> In my program below, I would expect the file "hello.bz2" to have been
> written once the close() function has been called, but it is not the
> case.  The contents are not actually written until I exit the scope in
> which the filtering_ostream object is defined (at which point the
> destructor presumably does the job).

reset() or pop() should work.

This also reflects a problem with filtering_ostream which I noticed only after
the feature freeze before the 1.33 release: copy calls close() on both its
arguments, but close() is a no-op for filtering_streams. Instead, close() should
probably call pop().

> (The file "some_text.txt"
> contains just the text "hello world!" so I would expect it not to be
> written until the file is closed.)

No, the implementation is free to flush the stream at any time. Also, copy
closes the stream.

> I would like to be able to do this explicitly and not have to rely on
> the destruction of the object - could you explain how can this be
> done?
>
> Another question: what should the second parameter to close() be?
> I've used BOOST_IOS::trunc here, but is there some other more
> appropriate value?

close() is meant to be called by the iostreams library; you shouldn't have to
call it yourself.

Thanks for using the iostreams library!

> Thanks,
>
> Paul Giaccone

-- 
Jonathan Turkanis
www.kangaroologic.com