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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.

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