------- Comment #4 from tstarling at wikimedia dot org 2010-09-07 17:18 ------- Benchmarking on Solaris indicates that cin.getline() takes only 1us per iteration there, but I don't think the source code is available, so it's hard to provide details.
However, I think that a huge speedup could be achieved by making basic_istream<char>::getline() into a simple wrapper around a GNU-specific virtual function in basic_streambuf. This would allow it to be specialised in stdio_sync_filebuf, where it could be implemented using fgets() or getdelim() instead of getc(). This would have the additional positive impact of making it atomic. Currently, cin.getline() does not properly lock the underlying libc stream with flockfile(). This means that if one thread is calling cin.getline(), and another thread is calling getc(), then cin.getline() may return mangled partial lines due to interleaved calls to getc() from the other thread. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45574
