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This procedure logically deletes a record from a KSAM file. CALL "CKDELETE" USING filetable, status
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In order to logically delete records from a KSAM file, you can use the procedure CKDELETE. If reuse is not specified, then a logically deleted record is marked for deletion, but is not physically removed from the file. The deletion mark makes such a record inaccessible but does not physically reduce the size of the file. The utility program FCOPY can be used to compact a KSAM file by copying only active records, excluding deleted records, to a new KSAM file. CKDELETE deletes the record at which the logical record pointer is currently positioned. Therefore, CKDELETE must be preceded by a call that positions the pointer. Parameters | |
- filetable
An 8 halfword record containing the number and name of the file, its input/output type, access mode, and a code indicating whether the previous operation was successful and if so what it was. (Refer to Filetable Parameter discussion earlier in this section.) - status
One halfword (two 8-bit characters) set to a pair of values upon completion of the call to CKDELETE indicating whether the call was successful and if not, why not. (Refer to Status Parameter discussion earlier in this section.)
Operation Notes | |
In order to delete a record, you should first read the record into the working storage section of your program with a call to CKREAD if in sequential mode, a call to CKREADBYKEY if in random mode, or a call to either if in dynamic mode. CKDELETE can be called only if the file is currently open for both input and output (input/output type =2). This allows the record to be read into your program's data area and then written back to the file with the delete mark. Following execution of CKDELETE, the deleted record can no longer be accessed. If the file was opened for shared access with CKOPENSHR, you must lock the file with CKLOCK before you can delete any records with CKDELETE. Because CKDELETE depends on the logical record pointer, the call to CKLOCK should precede the call that positions the pointer. The call to CKUNLOCK is then called after the call to CKDELETE. To illustrate, the sequence of calls in shared access should be:
CKLOCK <--- to lock file
CKSTART or CKREADBYKEY <--- to position pointer
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CKDELETE<--- to delete record at which pointer is positioned
CKUNLOCK<--- to unlock file
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Following the call to CKDELETE, the pointer is positioned to the next key following the key in the deleted record. The following examples show the use of CKDELETE for sequential access using CKREAD and for random access using CKREADBYKEY. The WORKING-STORAGE SECTION from Figure A-2 “Representation of KSAMFILE Used in COBOL Examples” and
the FINISH procedure from the CKCLOSE example are assumed for these examples. | | | |  | NOTE: If access is shared, the file must be opened with a call to CKOPENSHR and then locked before the call to CKSTART that initially sets the pointer. The file must remain locked while the records to be deleted are read and then marked for deletion. If the file is not locked before CKSTART is called, other users can change the file so that the record pointer points to the wrong record. | | | | |
In the first example, to delete all records whose primary key begins with "P", first position the file to the start of these records with CKSTART and then read each record with CKREAD and delete it with CKDELETE.
WORKING-STORAGE SECTION.
77 RELOP PIC S9(4) COMP.
77 KEYVAL PIC X(20).
77 KEYLOC PIC S9(4) COMP.
77 KEYLENGTH PIC S9(4) COMP.
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PROCEDURE DIVISION.
START.
MOVE 2 TO I-O-TYPE.
MOVE 0 TO A-MODE.
CALL "CKOPEN" USING FILETABLE, STAT.
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FIND-REC.
MOVE 0 TO RELOP.<--- test for equality between
primary key and KEY
MOVE "P" TO KEYVAL.
MOVE 3 TO KEYLOC.
MOVE 1 TO KEYLENGTH.<--- check first character only
CALL "CKSTART" USING FILETABLE, STAT, RELOP, KEYVAL, KEYLOC,
KEYLENGTH.
IF STATUS-KEY-1 = "0" THEN
GO TO READ-REC.
IF STAT = "23" THEN
DISPLAY "NO RECORD FOUND"
GO TO FINISH.
IF STATUS-KEY-1 = "9" THEN
CALL "CKERROR" USING STAT, RESULT
DISPLAY "CKERROR NO.=", RESULT
GO TO FINISH.
READ-REC.
CALL "CKREAD" USING FILETABLE, STAT, REC, RECSIZE.
IF STATUS-KEY-1 = "1" THEN
DISPLAY "END OF FILE REACHED"
GO TO FINISH.
IF STATUS-KEY-1 = "0" THEN
IF NAME OF REC NOT LESS THAN "Q "THEN
DISPLAY "DELETIONS COMPLETED"
GO TO FINISH;
ELSE GO TO DELETE-REC;
ELSE
DISPLAY "CKREAD ERROR, STATUS =", STAT
IF STATUS-KEY-1 = "9" THEN
CALL "CKERROR" USING STAT, RESULT
DISPLAY "CKERROR NO.", RESULT.
GO TO READ-REC.
DELETE-REC.
CALL "CKDELETE" USING FILETABLE, STAT.
IF STATUS-KEY-1 = "0" THEN
DISPLAY "DELETED"
GO TO READ-REC;
ELSE
DISPLAY "CKDELETE ERROR, STATUS = ", STAT
IF STATUS-KEY-1 = "9" THEN
CALL "CKERROR" USING STAT, RESULT
DISPLAY"CKERROR NO.=", RESULT
GO TO READ-REC.
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In the second example, a file containing the primary keys of those records to be deleted from a KSAM file is read into the working storage area DAT. These key values are used by CKREADBYKEY to locate and read the items to be deleted by CKDELETE.
PROCEDURE DIVISION.
START.
MOVE 2 TO I-O-TYPE, A-MODE.
CALL "CKOPEN" USING FILETABLE, STAT.
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READ-KEY.
READ DATA-FILE INTO DAT;
AT END GO TO FINISH.
CALL "CKREADBYKEY" USING FILETABLE, STAT, REC, NAME OF DAT, KEYLOC,
RECSIZE.
IF STATUS-KEY-1 = "0" THEN
GO TO DELETE-RECORD.
DISPLAY "CKREADBYKEY ERROR, STATUS = ",STAT.
IF STATUS-KEY-1 = "9" THEN
CALL "CKERROR" USING STAT, RESULT
DISPLAY "CKERROR ", RESULT
GO TO READ-KEY.
DELETE-RECORD.
CALL "CKDELETE" USING FILETABLE, STAT.
IF STATUS-KEY-1 = "0" THEN
DISPLAY REC, " DELETED"
GO TO READ-KEY.
DISPLAY "CKDELETE ERROR, STATUS =",STAT.
IF STATUS-KEY-1 = "9" THEN
CALL "CKERROR" USING STAT, RESULT
DISPLAY "CKERROR NO. =", RESULT.
GO TO READ-KEY.
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| | | | | NOTE: If access is shared, the file must be opened with a call to CKOPENSHR. A call to CKLOCK must precede the call to CKREADBYKEY. A call to CKUNLOCK must follow the CKDELETE error tests and should precede the return to READ-KEY. | | | | |
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