http://stackoverflow.com/questions/16772842/what-is-the-difference-between-cout-cerr-clog-of-iostream-header-in-c-when
cerr for errors
cout for normal output
clog for logging
The major difference is that std::cerr is not buffered like the other two.
std::cerr
cout 会将输出信息先写入缓存，而cerr会将消息直接输出到console
【C++】cerr，cout，clog
原文：http://www.cnblogs.com/cheermyang/p/6498283.html
