How to rollback lines from cout?
I'm coding a task monitoring, which updates tasks' progress using cout. I'd like to display one task progress per line, therefore I have to rollback several lines of the console.
I insist on "several" because \b does the job for one line, but does not erase \n between lines.
I tried std::cout.seekp(std::cout.tellp() - str.length()); but tellp() returns -1 (failure).
Answer
You can do cout << '\r'; to jump to the beginning of the current line, but moving upwards is system-specific. For Unix, see man termcap and man terminfo (and search for cursor_up). On ANSI-compatible terminals (such as most modern terminals available on Unix), this works to move up: cout << "\e[A";.
Don't try seeking in cout, it's unseekable most of the time (except when redirected to a file).
As mentioned in other answers, using the ncurses (or slang) library provides a good abstraction for terminal I/O on Unix.
Instead of filling with spaces (which is error-prone, because not every terminal is 80 characters wide), you can do \r + clr_eol: std::cout << "\r\e[K" << std::flush.