Using C or C++ I/O functions

Runtime messages and perror() messages are directed to the stderr standard stream output device.

Message output issued by a call to the printf() function is directed to stdout.

You can change the destination of printf() output by redirection. For example, 1>&2 on the command line at routine invocation redirects stdout to the stderr destination.

Table 1 lists the possible destinations of redirected stderr and stdout standard stream output.

Table 1. C/C++ redirected stream output
	Stderr not redirected	Stderr redirected to destination other than stdout	Stderr redirected to stdout
stdout not redirected	`stdout` to itself	`stdout` to itself	Both to `stdout`
stdout not redirected	`stderr` to itself	`stderr` to its other destination
stdout redirected to destination other than stderr	`stdout` to its other destination	`stdout` to its other destination	Both to the other `stdout` destination
stdout redirected to destination other than stderr	`stderr` to itself	`stderr` to its other destination
stdout redirected to stderr	Both to `stderr`	Both to the other `stderr` destination	When `stderr` and `stdout` are redirected to each other (this is not recommended), output from both is directed to whichever was specified first.

For more information about redirecting standard streams in C or C++, see z/OS XL C/C++ Programming Guide.