Re: [boost] Re: formatting manipulator for UTF-8

From: Thomas Matelich (sosedada_at_[hidden])
Date: 2000-08-22 11:55:59

Karl Nelson wrote:

> > Karl Nelson wrote:
> >
> > > This isn't a dark place, but rather just a bit of ambiguity.
> > > My current implementation used two formats in a row to mean
> > > "dump current and use this one".  However, that functionality
> > > could be dumped in place of the other meaning.   Also one would have
> > > to ask is the current behavior that extra arguments are placed
> > > in the stream appropriate as well.
> > >
> > >   cout << format("%d %d") << i << j << format("%d %d") << k << l;
> > >
> > > (is the second format bad because the first one forgot the endf
> > > or should the second flow to the first?)
>
> Perhaps if I write it as the streams will see it that will answer your
> question....
>
>      format_stream(cout,"%d %d"),
>        (strstream << decimal << i),
>        (strstream << decimal << j),
>      cout << string() << string("1") << string(" ") << string("2") << string(),
>      format_stream::new_format
>        (strstream << decimal << k),
>        (strstream << decimal << l),
>      cout << string() << string("3") << string(" ") << string("4") << string(),
>
> In other words all the strings are being spooled up in the
> a local variable via strstreams and then pushed to cout when
> all arguments are done.
>
> Since each format spooler its own local variable no globals
> are needed nor does it actually change the state of the
> stream until after it has all of its arguments.
>
> > I just got scared with this method.  The biggest problem I'm seeing here is a
> > global state.  What if I'm in a multithreaded situation?  I realize I'm going
> >  to
> > have problems writing to the same stream from two different threads, but woul
> > d
> > this maintain a different state for each stream?
>
> Since the manipulators are never applied to the cout stream directly
> but instead to a buffer you should never get any changes of state
> on your output.  (Nothing done in a format should be sticky)
> You should still lock the stream as having 2 threads dink with the same
> stream is asking for trouble.
>
> >I didn't look at the code s
> > o my
> > concern may be unfounded.
>
> Did that answer your question?

It was the statement about forgetting the endf that gave the impression of
globals.  I see that the question now is how does format handle recieving a format
parameter?  I believe that's the question you were asking above.

It seems like, if I'm understanding the code above, centering should be fairly
simple, unfortunately it would require more options like %15cs and some people
don't like having to remember things like that.  Personally, I think that's what
documentation is for.

Another thought with regards to the transition between formats.  How would it deal
with having the result of a format in another format?  Assuming we have centering,
something like so:
cout << format("%d %32cs") << 8 << format("Is %s's age") << name << endl;
Is this going to be workable?  Not that I necessarily think it should be but it is
a usage scenario that should be addressed.

--
Thomas O Matelich
Senior Software Designer
Zetec, Inc.
sosedada_at_[hidden]
tmatelich_at_[hidden]