Re: ios output width

James Kanze <>
Fri, 7 Dec 2007 07:42:16 -0800 (PST)
On Dec 7, 8:42 am, Ralf Goertz
<> wrote:

David Harmon wrote:

Ralf Goertz wrote

I'd like to use copy() to send the content of an integer container to
cout. How can I make sure that /all/ of them are printed with width 2?

You realize that by requiring std::copy you are doing it the hard
way? Homework?

No, it's not homework. Reading this newsgroup I got the
impression that using std::copy is the preferred way to output
containers. So yes I could have used a loop to do it. That is
not the point. I wonder why one can *permanently* switch an
output stream to another base but not to a width other than 0.
I thought that I had missed something, that's why I asked.

Alternatively, one might ask why one can set the length for a
single output, but one can't set the base for a single output.

I'm not really sure that there's much logic behind which is
which: width is volatile, and all of the others permanent. But
it's easy to get the other effect when you need it: all of my
manipulators restore the original state in their destructor, for
example (so any changes loose effect at the end of the full
expression), and it's pretty easy to add state, and manipulators
which manipulate it, as I did in my answer to your posting.

You could define an adapter class that is implicitly
constructed from the int, and use output_iterator<adapter>
to call your code to do the formatting.

Okay, thanks. But that surely is "doing it the hard way".

Not if it solves a general problem. Creating a class which
outputs an int, always with width 2, is doing it the hard way.
Creating a template class which outputs its type with the width
it reads from an additional state variable may require a little
more code to begin with (it took me about 15 minutes to write
and test -- where as writing the loop would probably take less
than a minute), but it could easily save work in the long run,
if the problem is frequent.

James Kanze (GABI Software)
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