c++ - 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 log file.

However, if I try to redefine clog to be the new stream it does not work because the new stream has the same rdbuf() as clog so the following has no effect:

clog.rdbuf(myTee.rdbuf());

So how can I modify the tee class to have its own rdbuf() which can then be the target of clog?

Thanks.

-William

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.