Using C or C++ I/O functions

C and C++ make a distinction between types of error output, and whether the output is directed to the MSGFILE destination or to one of the standard stream output devices, stderr or stdout.

Runtime messages and perror() messages are directed to the stderr standard stream output device. The default destination for stderr output is the MSGFILE ddname; you can change this default as discussed below.

Message output issued by a call to the printf() function is directed to stdout. For TSO/E, stdout defaults to the terminal. When running batch (MVS™, IMS™, or TSO/E) or IMS online, stdout attempts by default to open one of several ddnames in the following order of precedence, which is made to open SYSOUT=* as a data set:

SYSPRINT
SYSTERM
SYSERR

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 types of C/C++ output, the types of messages associated with them, and the destination of the message output.

Table 1. C and C++ message output
Type of output	Type of message	Produced by	Default destination
MSGFILE output	Language Environment messages (CEExxxx)	Language Environment unhandled conditions	MSGFILE ddname
MSGFILE output	C library messages	C/C++ unhandled conditions (EDCxxxx)	MSGFILE ddname
`stderr` messages	`perror()` messages (EDCxxx)	Issued by a call to `perror()`	MSGFILE ddname
`stderr` messages	User output sent explicitly to `stderr`	Issued by a call to `fprintf()`	MSGFILE ddname
`stdout` messages	User output sent explicitly to `stdout`	Issued by a call to `printf()`	`stdout`

You can control the destination of stderr and stdout output by using the Language Environment MSGFILE runtime option, the C freopen() function, or by invoking redirection services at run time.

Table 2 lists the possible destinations of redirected stderr and stdout standard stream output.

Table 2. C/C++ redirected stream output
Action	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 MSGFILE	`stderr` to its other destination	n/a
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 MSGFILE	`stderr` to its other destination	n/a
stdout redirected to stderr	Both to MSGFILE	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.