c++ - redirect std::cout to a custom writer

Question

I want to use this snippet from Mr-Edd's iostreams article to print std::clog somewhere.

#include <iostream>
#include <iomanip>
#include <string>
#include <sstream>

int main()
{
    std::ostringstream oss;

    // Make clog use the buffer from oss
    std::streambuf *former_buff =
        std::clog.rdbuf(oss.rdbuf());

    std::clog << "This will appear in oss!" << std::flush;

    std::cout << oss.str() << '\n';

    // Give clog back its previous buffer
    std::clog.rdbuf(former_buff);

    return 0;
}

so, in a mainloop, I will do something like

while (! oss.eof())
{
    //add to window text somewhere
}

Here's the ostringstream docs but I'm having trouble understanding the best way to do this. I have a method that displays the text, I just want to call it with any data in the ostringstream.

What is the easiest/best way to get anything sent to std::clog redirected to a method of my choice? is it as above, and fill in the while !eof part (not sure how), or is there a better way, say by overloading some 'commit' operator somewhere that calls my method? I'm loking for quick and easy, I really don't want to start defining sinks and such with boost iostreams as the article does - that stuff is way over my head.

Answer 1

I encourage you to look at Boost.IOStreams. It seems to fit your use-case nicely, and using it is surprisingly simple:

#include <boost/iostreams/concepts.hpp> 
#include <boost/iostreams/stream_buffer.hpp>
#include <iostream>

namespace bio = boost::iostreams;

class MySink : public bio::sink
{
public:
    std::streamsize write(const char* s, std::streamsize n)
    {
        //Do whatever you want with s
        //...
        return n;
    }
};

int main()
{
    bio::stream_buffer<MySink> sb;
    sb.open(MySink());
    std::streambuf * oldbuf = std::clog.rdbuf(&sb);
    std::clog << "hello, world" << std::endl;
    std::clog.rdbuf(oldbuf);
    return 0;
}