Use of std::flush in std::cerr

[zixin96]

The book: Ray Tracing in One Weekend
Specific location: 2.3. Adding a Progress Indicator, Listing 3

Hello everyone! I recently started to learn about the usage of std::flush and found that our code used
std::cerr << "\rScanlines remaining: " << j << ' ' << std::flush;.

However, since std::cerr is not buffered like std::cout, wouldn't this make our std::flush redundant? If not, what is the purpose of std::flush here?

[hollasch]

Thank you! I didn't realize that std::cerr is inherently unbuffered. Given that, we have two solutions:

std::cerr << "\rScanlines remaining: " << j << ' ';

and

std::clog << "\rScanlines remaining: " << j << ' ' << std::flush;.

I'd never heard of std::clog until now, but it actually looks like a more accurate channel for this particular content (that is, logging the current scanline in progress). Given that, I lean toward keeping the flush and using std::clog instead. Thoughts?

[zixin96]

Thanks for the quick reply. I agree with you on using std::clog. It makes it clear that we want to log our progress.

[hollasch]

Fixed in #936 and #942.