Predefined streams for C++

z/OS® XL C++ provides the following predefined streams:
cin
The standard input stream
cout
The standard output stream
cerr
The standard error stream, unit-buffered such that characters sent to this stream are flushed on each output operation
clog
The buffered error stream

All predefined streams are tied to cout. When you use cin, cerr, or clog, cout gets flushed sending the contents of cout to the ultimate consumer.

z/OS C standard streams create all I/O to I/O streams:

When redirecting or intercepting a C standard stream, the corresponding C++ standard stream becomes redirected. This applies unless you redirect an I/O stream. See Using C and C++ standard streams and redirection for more information.