Boost logo

Boost :

From: Brian Braatz (brianb_at_[hidden])
Date: 2005-02-27 14:56:51


However, I am NOT (yet) an expert in the Iostreams library so please
excuse me if I am missing something obvious.

I add 2 sinks

       filtering_ostream out;
        out.push(file_sink("Report.txt"));
        out.push(cout);

I get an exception thrown on the second one (regardless of which one
goes in first)

In searching the archives, I noticed this mail:

http://tinyurl.com/6soeb

where Johnathon Turkis writes:

"For this we need to define an OutputFilter which stores a reference to
an ostream and has a member function 'write' which forwards all
characters to the stored ostream as well as to the downstream sink
(you don't need to understand the following code -- the point is that
it's just a few lines):

        struct tee : boost::io::output_filter {
             tee(std::ostream& dest) : dest(dest) { }

             template<typename Sink>
             void write(Sink& snk, char* s, std::streamsize n)
             {
                  // Write to the downstream Sink
                  boost::io::write(snk, s, n);

                  // Write to the stored ostream:
                  dest.write(s, n);
             }

             std::ostream& dest;
        };

We use the tee as follows. Given two ostreams

        ostream first;
        ostream second;

we define a filtering_ostream which passes data through the tee to
both streams:

        filtering_ostream out;
        out.push(tee(first));
        out.push(second);
        out << "this gets written to both ostreams\n";
"

Which looks "good" except I suspect the library has changed since the
above is not compiling for me under VC71. (it complains about wanting a
Put() instead of a write())..

Any help appreciated- and also - a request- if "tee" functionality could
be officially implemented in the streaming lib for output sinks.

OR if it already is, I request that how do to it be spelled out more
clearly in the documentation.

Thanks

Brian Braatz


Boost list run by bdawes at acm.org, gregod at cs.rpi.edu, cpdaniel at pacbell.net, john at johnmaddock.co.uk