Inside COBOL #53 (Control Y trap processing)
by
Shawn Gordon
President
The Kompany
You ever notice how you can use the
Our tip this month comes by way of Tim Ericson at Denkor Dental Management Corp. (the NewsWire hat is in the mail). I would like to thank Tim, and Tim would like to thank the HP COBOL II/XL Programmer’s Guide, pages 4-55 and 4-56. See figure 1 for an example of the code that arms, and handles the
Ok, let’s go over what is going to happen here. Tim’s comments at the top of the code tell you how to use the program, but let’s talk about what may not be so obvious. First the call to HPMYPROGRAM will return the fully qualified MPE file name of the program that is calling it, which we will need for our next call to HPGETPROCPLABEL. This intrinsic will search for the named procedure label, in our case the entry for “CONTROL-Y-TRAP” to use as the interrupt address. It starts searching from the named program until it finds the procdure label, and returns the address into our variable PLABEL. We then call XCONTRAP, which is the actual trap handler. Here we pass the PLABEL of our interrupt, and the intrinsic will return the procedure label of the current address in the code.
This subroutine should only have to be called once from your main program. Once the trap is enabled, any time the user hits
Some good applications of a control Y trap is when you are serially reading large amounts of data from a data set or a flat file. If you are keeping counters then the user can easily tell what their progress is, and dump out if desired. This can be a handy debugging tool as well if you use it correctly.
Well that wraps it up for this month, next month I am finally going to get to COBOL macros like I’ve been promising for months. Keep those cards and letters coming.
Figure 1
$PAGE
$CONTROL BOUNDS, DYNAMIC, LIST, POST85, SOURCE
****************************************************************
* *
* CONTROLY.SOURCE 11/15/94 T. ERICSON *
* *
* THIS SUBPROGRAM ARMS A CONTROL-Y TRAP, AND MUST BE CALLED *
* FROM A MAIN PROGRAM. THE FOLLOWING CODE MUST BE INCLUDED *
* IN THE MAIN PROGRAM: *
* *
* . *
* . *
* . *
* WORKING-STORAGE SECTION. *
* *
* 01 CONTROL-Y EXTERNAL PIC X. *
* 88 CONTROL-Y-HIT VALUE "Y". *
* 88 CONTROL-Y-OFF VALUE "N". *
* *
* . *
* . *
* . *
* PROCEDURE DIVISION. *
* *
* CALL "ARM-CONTROL-Y". *
* *
* . *
* . *
* . *
* LOOP-POINT. *
* *
* . *
* . *
* . *
* IF CONTROL-Y-HIT *
* DISPLAY "DO YOU WISH TO CONTINUE? " *
* WITH NO ADVANCING *
* ACCEPT ANSWER *
* IF ANSWER = "N" *
* STOP RUN *
* END-IF *
* SET CONTROL-Y-OFF TO TRUE. *
* *
* GO TO LOOP-POINT. *
* . *
* . *
* . *
* *
* COMPILE AND LINK THE TWO SOURCE FILES TOGETHER LIKE THIS: *
* *
* :COB85XL MAINSOURCE, USLMAIN *
* :COB85XL CONTROLY.SOURCE, USLSUB *
* :LINK FROM=USLMAIN, USLSUB; TO=PROGRAMFILE *
* *
****************************************************************
$PAGE
IDENTIFICATION DIVISION.
PROGRAM-ID. ARM-CONTROL-Y.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 PROCNAME PIC X(20) VALUE "!control_y_trap!".
01 PLABEL PIC S9(09) COMP.
01 OLDPLABEL PIC S9(09) COMP.
01 PROGFILE PIC X(40).
01 CONTROL-Y EXTERNAL PIC X.
88 CONTROL-Y-HIT VALUE "Y".
88 CONTROL-Y-OFF VALUE "N". 8.2
PROCEDURE DIVISION.
01-START.
CALL INTRINSIC "HPMYPROGRAM"
USING PROGFILE.
CALL INTRINSIC "HPGETPROCPLABEL"
USING PROCNAME PLABEL \\ PROGFILE.
CALL INTRINSIC "XCONTRAP"
USING PLABEL OLDPLABEL.
EXIT PROGRAM.
ENTRY "CONTROL-Y-TRAP".
DISPLAY "< CONTROL Y >".
DISPLAY " ".
SET CONTROL-Y-HIT TO TRUE.
CALL INTRINSIC "RESETCONTROL".