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From: Larry Evans on 19 Jan 2010 21:14
On Jan 18, 8:43 am, "dietmar_ku...(a)yahoo.com"
<dietmar.ku...(a)gmail.com> wrote:
[snip]

> A much
> more sensible (and much easier to implement) approach is to create a
> filtering stream buffer which just replaces every newline by a newline
> followed by the appropriate number of spaces. In its simplest form
> (non-optimized) form it just takes a few lines of code:
>
> struct indentbuf: std::streambuf
> {
> indentbuf(std::streambuf* sbuf, int indent):
> m_sbuf(sbuf), m_indent(indent) {}
> private:
> int_type overflow(int_type c)
> {
> if (c != std::char_traits::eof())
> {
> this->m_sbuf->sputc(c);
> if (c == '\n')
> {
> std::fill_n(std::ostreambuf_iterator<char>(this->m_sbuf),
> this->m_indent, ' ');
> }
> }
> return std::char_traits::not_eof(c);
> }
> int sync() { return this->m_sbuf->pubsync(); }
> std::streambuf* m_sbuf;
> int m_indent;
> };
>
> You'd create a new std::ostream with using something like this:
>
> indentbuf sbuf(std::cout.rdbuf(), 2);
> std::ostream indentstream(&sbuf);
>
> Obviously, if you want to use indentation with an existing stream you
> can replace that stream's stream buffer with an indentbuf as long as
> objects get the proper live time.
[snip]

You'd also need a way to change indentbuf::m_indent. This would
require using rdbuf() and then casting to indentbuf*.
Althought boost/iostreams has (I assume) a lot of overhead,
this is done automatically in the boost vault code mentioned
in my post.

I would guess the iostreams implementation does something like
your suggestion behind the scenes since the acknowledgments:

http://www.boost.org/doc/libs/1_41_0/libs/iostreams/doc/acknowledgments.html

mention your and Kanze's names.

-regards,
Larry


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From: Larry Evans on 19 Jan 2010 21:15
On Jan 18, 8:43 am, "dietmar_ku...(a)yahoo.com"
<dietmar.ku...(a)gmail.com> wrote:
[snip]

> Obviously, if you want to use indentation with an existing stream you
> can replace that stream's stream buffer with an indentbuf as long as
> objects get the proper live time.
[snip]

I believe this is illustrated by the indent_scoped_ostreambuf.zip file
in the boost vault directory:

http://www.boostpro.com/vault/index.php?&directory=Input%20-%20Output


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