CKREADBYKEY
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CALL "CKREADBYKEY" USING filetable, status, record, key,
keyloc, recordsize
Records can be read from a KSAM file in an order determined
by key value. This order need not be sequential; in fact, it can
be any order you specify. This type of access is used to access
individual records in random order by key value.
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.
- status
One halfword (two 8-bit characters) set to a pair of values upon completion of the call to CKREADBYKEY indicating whether the call was successful and if not why not.
- record
A record defined in the WORKING-STORAGE SECTION into which the contents of a record located by key value is read.
- key
An item whose value is used by CKREADBYKEY to locate the record to be read. Key values in the file identified by filetable are compared to the value of key until the first record with an equal value is found.
- keyloc
One halfword integer (S9(4)COMP) set to the starting character position of the key in the KSAM data record (first position is character 1). The keyloc parameter identifies the file key to be compared with key.
- recordsize
An integer (S9(4)COMP) containing the length in characters of the record being read; it must be less than or equal to the maximum record length established for the file at creation.
Operation Notes
In order to use the CKREADBYKEY procedure, the file must be opened for either input or input/output. The access mode can be either random or dynamic, but must not be sequential. Execution of CKREADBYKEY causes the value of key to be compared to the value of the key at location keyloc in the KSAM file data records. When a key is found whose value is identical to that of key, the record pointer is moved to the beginning of that record and the record is read into the location record. If no record can be found whose key value equals that of key, an invalid key condition is diagnosed and status is set to the value 23. Successful execution of CKREADBYKEY is indicated by the value 0 in the left byte of status. Unsuccessful execution is indicated by either the invalid key return or by a value of 9 in the left byte of status. In order to delete records in random or dynamic mode, CKREADBYKEY must be called before executing CKDELETE. It is not required prior to CKREWRITE. In the following examples, update information is read into the area called DAT in the WORKING-STORAGE SECTION. (Note that in this as in the preceding examples, the WORKING-STORAGE SECTION from Figure A-2 "Representation of KSAMFILE Used in COBOL Examples" continues to be useful.) In the first example, the primary keys of records in KSAMFILE are searched for values matching the value read into NAME in the DAT record; in the second example, an alternate key at location 23 is searched for values matching the value read into PHONE in the DAT record. Read a record located by its primary key value:
DATA DIVISION.
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WORKING-STORAGE SECTION.
77 KEYLOC PIC S9(4) COMP.
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PROCEDURE DIVISION.
START.
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MOVE 2 TO I-O-TYPE, A-MODE. <-- prepare to open for
<-- input/output, dynamic access
CALL "CKOPEN" USING FILETABLE, STAT.
IF STATUS-KEY-1 = "9" THEN
CALL "CKERROR" USING STAT, RESULT
DISPLAY "CKOPEN ERROR NO. ", RESULT.
IF STATUS-KEY-1 NOT="O" THEN
DISPLAY "CKOPEN FAILED"
STOP RUN.
FIND-RECORD.
READ NEW-DATA INTO DAT; <--- read update records
AT END GO TO FINISH.
MOVE 3 TO KEYLOC.
CALL "CKREADBYKEY" USING FILETABLE, STAT, REC, NAME OF DAT,
KEYLOC, RECSIZE.
IF STAT = "00" THEN
DISPLAY "RECORD FOUND", REC
GO TO FIND-RECORD.
IF STAT = "23" THEN
DISPLAY "RECORD NOT FOUND,KEY=", NAME OF DAT
GO TO FIND-RECORD.
IF STATUS-KEY-1 = "9" THEN
CALL "CKERROR" USING STAT, RESULT
DISPLAY "ERROR NO. ", RESULT
GO TO FIND-RECORD.
To find a record by the value of an alternate key, simply change two statements
in the preceding example so that KEYLOC contains the location
of the alternate key and the key value for comparison is found
in item PHONE OF DAT rather than in
NAME OF DAT:
FIND RECORD.
READ NEW-DATA INTO DAT;
AT END GO TO FINISH.
MOVE 23 TO KEYLOC.
CALL "CKREADBYKEY" USING FILETABLE, STAT, REC, PHONE OF DAT,
KEYLOC, RECSIZE.
|
CKREAD |
CKREWRITE |