This is implementation dependent. Check with your compiler’s documentation.
For example, suppose you want to do binary I/O using std::cin and std::cout. Unfortunately there is no standard way to cause std::cin, std::cout, and/or std::cerr to be opened in binary mode. Closing the streams and attempting to reopen them in binary mode might have unexpected or undesirable results. On systems where it makes a difference, the implementation might provide a way to make them binary streams, but you would have to check the implementation specifics to find out.