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 
#include 
#include 

        

Answer 1

I needed to grab outputs to std::cout and std::cerr from third party libraries and log them using log4cxx, and still retaining the original outputs.

This is what I came up with. It's pretty straight-forward:

• I replace the old buffer of an ostream (like std::cout) with my own class so that I get access to what ever is written to it.

• I also create a new std::ostream object with the old buffer so that I can continue to get the output to my console, besides sending it to my logger. Which I find kind of handy.

Code:

class intercept_stream : public std::streambuf{
public:
    intercept_stream(std::ostream& stream, char const* logger):
      _logger(log4cxx::Logger::getLogger(logger)),
      _orgstream(stream),
      _newstream(NULL)
    {
        //Swap the the old buffer in ostream with this buffer.
        _orgbuf=_orgstream.rdbuf(this);
        //Create a new ostream that we set the old buffer in
        boost::scoped_ptr os(new std::ostream(_orgbuf));
        _newstream.swap(os);
    }
    ~intercept_stream(){
        _orgstream.rdbuf(_orgbuf);//Restore old buffer
    }
protected:
    virtual streamsize xsputn(const char *msg, streamsize count){
        //Output to new stream with old buffer (to e.g. screen [std::cout])
        _newstream->write(msg, count);
        //Output to log4cxx logger
        std::string s(msg,count);
        if (_logger->isInfoEnabled()) {
            _logger->forcedLog(::log4cxx::Level::getInfo(), s, LOG4CXX_LOCATION); 
        }
        return count;
    }
private:
    log4cxx::LoggerPtr _logger;
    std::streambuf*    _orgbuf;
    std::ostream&      _orgstream;
    boost::scoped_ptr  _newstream;
};

Then to use it:

std::cout << "This will just go to my console"<