How to redefine clog to tee to original clog and a log file?

Question

I saw a useful start here:

http://www.cs.technion.ac.il/~imaman/programs/teestream.html

And it works great to make a new stream which goes to both clog and a

Answer 1

Here is the class I created that seems to do the job, thanks to all who helped out!

-William

class TeeStream : public std::basic_filebuf >
{
private:
  class FileStream : public std::ofstream {
  public:
    FileStream()
      : logFileName("/my/log/file/location.log") {
      open(logFileName.c_str(), ios::out | ios::trunc);

      if (fail()) {
        cerr << "Error: failed to open log file: " << logFileName << endl;
        exit(1);
      }
    }
    ~FileStream() {
      close();
    }

    const char *getLogFileName() const {
      return logFileName.c_str();
    }

  private:
    const string logFileName;

  };

public:
  typedef std::char_traits traits;
  typedef std::basic_filebuf baseClass;

  TeeStream()
    :  baseClass(),
       _logOutputStream(),
       _clogBuf(clog.rdbuf()),
       _fileBuf(_logOutputStream.rdbuf()) {
    clog.rdbuf(this);
    _logOutputStream << "Log file starts here:" << endl;
  }
  ~TeeStream() {
    clog.rdbuf(_clogBuf);
  }

  int_type overflow(char_type additionalChar =traits::eof()) {
    const int_type eof = traits::eof();
    const char_type additionalCharacter = traits::to_char_type(additionalChar);
    const int_type result1 = _clogBuf->sputc(additionalCharacter);
    const int_type result2 = _fileBuf->sputc(additionalCharacter);

    if (traits::eq_int_type(eof, result1)) {
      return eof;
    } else {
      return result2;
    }
  }

  int sync() {
    const int result1 = _clogBuf->pubsync();
    const int result2 = _fileBuf->pubsync();

    if (result1 == -1) {
      return -1;
    } else {
      return result2;
    }
  }

private:
  FileStream _logOutputStream;
  streambuf * const _clogBuf;
  streambuf * const _fileBuf;

};