Cursor positioning on a subfile display is a casual afterthought for most programmers, if it is ever considered. It is application users who are concerned with cursor positioning. After all, for application users, interactive displays and reports are not just the interface to the real application- they are the application.
Deletion of subfile records causes a special problem. Typically, after subfile records are deleted, the subfile is rebuilt for redisplay. Where should the cursor be positioned? It is much more effective to position the cursor at the first subfile record after the last deleted record than to position it at the top of the redisplayed subfile, especially if the last deleted record is several pages deep into the display. How is this accomplished?
I have included two figures to illustrate my technique. Figure 1 shows the DDS of a typical subfile display file, and Figure 2 shows the RPG III program that uses the subfile. To determine the cursor position, several elements are required. First, the relative record number (RRN) of the last record displayed in the original file must be captured. This RRN can be captured either from the system data structure or by moving the RRN of each subfile record written to a save field, TRRN1inthisexample.
Add 1 to the RRN of the last subfile record deleted, and subtract the number of subfile records deleted. The cursor should be positioned at the correct RRN of the rebuilt subfile. For example, if the last deleted subfile record was record number 15 and you deleted 3 subfile records, position the cursor at record number 13 (15+1-3).
Rebuild the subfile one page at a time, until the total of subfile records in the rebuilt display is greater than or equal to the RRN of the subfile record at which the cursor will be positioned. No more subfile pages are required, unless the application user rolls the display forward again.
One final trap remains for the unwary programmer. The first page of the subfile will be displayed, unless the RRN of the subfile record to be positioned to is moved into DSP1. This is the DDS variable attached to the SFLRCDNBR(CURSOR) keyword.
Catharine Minor has 15 years programming experience on IBM midrange computers. She can be reached by email at
Figure 1: Typical subfile display file
A R SFL1 SFL
A 70 SFLNXTCHG
ARRN1 5S 0H
A OPT 1A B 7 3
A 74 DSPATR(RI)
A CUSNBR 5 0O 7 7EDTCDE(Z)
A CUSNAM 25A O 7 14
*================================================================
A R SFC1 SFLCTL(SFL1)
A SFLSIZ(9999)
A SFLPAG(0010)
A OVERLAY
A 71 SFLDSP
A 72 SFLDSPCTL
A N72 SFLCLR
A 73 SFLEND(*MORE)
A DSP1 4S 0H SFLRCDNBR(CURSOR)
A 1 15'Select record'
A DSPATR(HI)
A 3 2'1=Select'
A COLOR(BLU)
A 3 13'2=Display'
A COLOR(BLU)
A 3 25'4=Delete'
A COLOR(BLU)
A 5 7'Record'
A DSPATR(HI)
A 6 2'Sel'
A DSPATR(HI)
A 6 8'Nbr'
A DSPATR(HI)
A 6 14'Description'
A DSPATR(HI)
FCUSMST UF E K DISK
FDSP CF E WORKSTN
F KINFDS INFDS
F RRN1 KSFILE SFL1
*****************************************************************
IINFDS DS
I 369 369 AID
I B 370 3710CURSOR
I B 378 3790LRRN
*================================================================
I 9999 C SFLMAX
I 10 C SFLPAG
*****************************************************************
* Mainline.
*
C EXSR $LSFL1 load first page
*
C *INKL DOWNE*ON F12=Exit
C MOVE *OFF *IN71 SFLDSP
C MOVE *ON *IN72 SFLDSPCTL
C TRRN1 IFGT 0 TRRN1=0 = no rec
C MOVE *ON *IN71 SFLDSP
C Z-ADDLRRN1 DSP1 saved last RRN
C ENDIF TRRN1 0
*
C EXFMTSFC1 *
C Z-ADDLRRN LRRN1 sv sflcsrrrn
* ... process subfile
C EXSR $PSFL1
Figure 2: Positioning the subfile cursor in RPG III
* ... record deleted, position cursor
C DLTFLG IFEQ *ON records dlted
* ... svrrn1 = (svrrn1 + 1) - dlt#
C ADD 1 SVRRN1 calc cursor
C SUB DLT# SVRRN1 RRN
* ... clear and rebuild subfile
C EXSR $CSFL1 clear SFL1
C EXSR $LSFL1 load SFL1
* ... read and load subfile records to page of position to record
C TRRN1 DOWLTSVRRN1
C *IN73 ANDNE*ON SFLEND
C EXSR $LSFL1 load SFL1
C ENDDO TRRN1 <> DSP1
*
C Z-ADDSVRRN1 LRRN1
* ... Correct cursor position
C *IN73 IFEQ *ON EOF
C SVRRN1 ANDGTTRRN1
C Z-ADDTRRN1 LRRN1
C ENDIF *
C ENDIF *
C ENDDO *
C MOVE *ON *INLR
*=====================================================================
* $LSFL1: Load SFL1
*
C $LSFL1 BEGSR *
C TRRN1 IFLT SFLMAX tot rrn < 9999
C Z-ADDTRRN1 RRN1
C CLEAROPT
*
C 1 DO SFLPAG COUNT
C READ CUSMST 40 *
C *IN40 IFEQ *ON EOF
C LEAVE
C ENDIF *
C ADD 1 RRN1 increment rrn
*...firstrecordonSFLpage
C COUNT IFEQ 1
C Z-ADDRRN1 LRRN1
C ENDIF
* ... write SFL record
C WRITESFL1
C ENDDO
* ... capture total rrn in subfile
C Z-ADDRRN1 TRRN1
C ENDIF tot rrn < 9999
*
C ENDSR
*=====================================================================
* $PSFL1: Process SFL1
*
C $PSFL1 BEGSR *
C MOVE *OFF DLTFLG
C CLEARSVRRN1
C CLEARDLT#
C Z-ADD1 RRN1 *
C READCSFL1 40
C *IN40 DOWNE*ON not EOF
C Z-ADDRRN1 SVRRN1
C Z-ADDRRN1 DSP1
* ... deletion specified
C OPT IFEQ '4' 4=Delete
CEXSR $DLT
C MOVE *ON DLTFLG
CADD 1 DLT#
C ENDIF
C UPDATSFL1
*
C READCSFL1 40 *
C ENDDO *
C ENDSR
*=====================================================================
* DCLVAR: Declare variables.
*
C DCLVAR BEGSR *
C MOVE *BLANK BYTE 1
C Z-ADD0 INT 50 *
C *LIKE DEFN INT COUNT
C *LIKE DEFN INT DLT#
C *LIKE DEFN BYTE DLTFLG
C *LIKE DEFN INT LRRN1
C *LIKE DEFN INT RRN1
C *LIKE DEFN INT SVRRN1
C *LIKE DEFN INT TRRN1 *
C ENDSR
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