COBOL Manual for TNS and TNS/R Programs

Terminal Input and Output

HP COBOL Manual for TNS and TNS/R Programs—522555-006

29-8

Terminal Associated With a Command Interpreter

When a command interpreter has a terminal open for its IN and OUT file, an

HP COBOL process can open that terminal as a file only if it opens it for shared access

(the default). It cannot open such a terminal for exclusive access, even if the command

interpreter does not accept messages from or send messages to that terminal for the

duration of the HP COBOL process’s execution. If you want an HP COBOL process to

have exclusive use of a terminal, no command interpreter can have the terminal open.

To free a terminal that is running TACL for use as a file by an HP COBOL program,

enter the TACL command PAUSE.

Terminal Not Associated With a Command Interpreter

When a terminal is not connected to a command interpreter, an HP COBOL process

can open it, read from it, write to it, or close it like any other file. See Using a Terminal

as a File.

Non-COBOL Modules

If your program consists of modules written in different languages, the modules can

share the standard files—the predefined files called “standard input,” “standard output,”

and “standard log” (except that FORTRAN modules cannot share “standard log”

because FORTRAN does not support it). The standard input, output, and log file can

be a terminal.

If you want to do mixed-language programming, compiling your program to run in the

CRE is highly recommended. Although mixed-language programming is possible in the

non-CRE environment, it is very limited because of incompatibilities between different

languages’ run-time libraries. The CRE supports the languages HP C, HP COBOL,

FORTRAN, Pascal, and TAL. For more information about the CRE in general and on

mixed-language programs sharing standard files in particular, see the CRE

Programmer’s Guide.

Getting Break Ownership

When you press Break on a terminal, the process that owns Break receives a system

message on $RECEIVE. A process discovers that Break has been pressed by reading

$RECEIVE. An HP COBOL process, lacking the ability to perform NOWAIT input and

output directly, must open $RECEIVE with an OPEN statement with a TIME LIMITS

phrase and then try to read $RECEIVE from time to time. If a READ statement fails

because it timed out, Break was not pressed.