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

If you really want to keep using std::clog for the tee instead of sending output to a different stream, you need to work one level lower: Instead of deriving from ostream, derive from streambuf. Then you can do this:

fstream logFile(...);
TeeBuf tbuf(logFile.rdbuf(), clog.rdbuf());
clog.rdbuf(&tbuf);

For more information on how to derive your own streambuf class, see here.