15.14.1 Synchronization with C’s Standard Streams
By default, the eight C++ standard streams — the four narrow character streams cin, cout, cerr,
and clog, and their wide-character counterparts — are synchronized with the corresponding files
from the C standard library: stdin, stdout, and stderr. By default, clog and wclog use the
same stream buffer as cerr and wcerr, respectively. Thus, they are also synchronized with stderr
by default, although there is no direct counterpart in the C standard library.