The following example shows how you might process a linked list, that is, a chained list of data items.
For this example, picture a chained list of data that consists of individual salary records. The following figure shows one way to visualize how the records are linked in storage. The first item in each record except the last points to the next record. The first item in the last record contains a null value (instead of a valid address) to indicate that it is the last record.
The high-level logic of an application that processes these records might be:
Obtain address of first record in chained list from routine Check for end of the list DO UNTIL end of the list Process record Traverse to the next record END
The following code contains an outline of the calling program, LISTS, used in this example of processing a chained list.
IDENTIFICATION DIVISION.
PROGRAM-ID. LISTS.
ENVIRONMENT DIVISION.
DATA DIVISION.
******
WORKING-STORAGE SECTION.
77 PTR-FIRST POINTER VALUE IS NULL. (1)
77 DEPT-TOTAL PIC 9(4) VALUE IS 0.
******
LINKAGE SECTION.
01 SALARY-REC.
02 PTR-NEXT-REC POINTER. (2)
02 NAME PIC X(20).
02 DEPT PIC 9(4).
02 SALARY PIC 9(6).
01 DEPT-X PIC 9(4).
******
PROCEDURE DIVISION USING DEPT-X.
******
* FOR EVERYONE IN THE DEPARTMENT RECEIVED AS DEPT-X,
* GO THROUGH ALL THE RECORDS IN THE CHAINED LIST BASED ON THE
* ADDRESS OBTAINED FROM THE PROGRAM CHAIN-ANCH
* AND CUMULATE THE SALARIES.
* IN EACH RECORD, PTR-NEXT-REC IS A POINTER TO THE NEXT RECORD
* IN THE LIST; IN THE LAST RECORD, PTR-NEXT-REC IS NULL.
* DISPLAY THE TOTAL.
******
CALL "CHAIN-ANCH" USING PTR-FIRST (3)
SET ADDRESS OF SALARY-REC TO PTR-FIRST (4)
******
PERFORM WITH TEST BEFORE UNTIL ADDRESS OF SALARY-REC = NULL (5)
IF DEPT = DEPT-X
THEN ADD SALARY TO DEPT-TOTAL
ELSE CONTINUE
END-IF
SET ADDRESS OF SALARY-REC TO PTR-NEXT-REC (6)
END-PERFORM
******
DISPLAY DEPT-TOTAL
GOBACK.
To increment addresses received from another program, you could set up the LINKAGE SECTION and PROCEDURE DIVISION like this:
LINKAGE SECTION.
01 RECORD-A.
02 HEADER PIC X(12).
02 REAL-SALARY-REC PIC X(30).
. . .
01 SALARY-REC.
02 PTR-NEXT-REC POINTER.
02 NAME PIC X(20).
02 DEPT PIC 9(4).
02 SALARY PIC 9(6).
. . .
PROCEDURE DIVISION USING DEPT-X.
. . .
SET ADDRESS OF SALARY-REC TO ADDRESS OF REAL-SALARY-REC
The address of SALARY-REC is now based on the address of REAL-SALARY-REC, or RECORD-A + 12.
related tasks
Using pointers to process a chained list