Problem:

Use the following program as an example and a template, when you need to write a COBOL program that will rebuild an existing indexed file.  The program reads the file from beginning to end and writes each record to a new file.

This is a way of creating a fresh version of the indexes and their B-trees, and of removing records that were marked for deletion but weren't yet physically deleted, and of otherwise getting the file into a new and fresh state.  It is an alternative to using the "rebuild infile, outfile" command.

Resolution:

The example "rebuild" program below is based on the demonstration program "stockioa.cbl", which gets installed with the Server Express product, and can be found in the directory $COBDIR/demo/locking.  Before running the example "rebuild" program below, perform the following steps:

mkdir /tmp/test-rbld

cd $COBDIR/demo/locking

cp stockioa.cbl /tmp/test-rbld

cd /tmp/test-rbld

cob stockioa.cbl

cobrun stockioa

Press "1", then function key 4, to add a record to the file, then press ESC, then "n" for "not wish to restart".  These actions will create an indexed file named "MUSTOCK.DAT".

Note that the following is a complete program (not a fragment), and will compile as written:

000001 $SET IDXFORMAT"8"

000002 $SET KEYCOMPRESS"7"

000003 $SET DATACOMPRESS"1"

000004

000005  SELECT STOCK-FILE-OLD ASSIGN TO "MUSTOCK.DAT"

000006          ORGANIZATION INDEXED

000007          ACCESS DYNAMIC

000008          RECORD KEY STOCK-KEY-OLD.

000009

000010  SELECT STOCK-FILE-NEW ASSIGN TO "MUSTOCK-NEW"

000011          ORGANIZATION INDEXED

000012          ACCESS DYNAMIC

000013          RECORD KEY STOCK-KEY-NEW.

000014

000015  DATA DIVISION.

000016  FILE SECTION.

000017

000018  FD  STOCK-FILE-OLD.

000019  01  STOCK-RECORD-OLD.

000020      03  STOCK-KEY-OLD                    PIC 9(06).

000021      03  STOCK-DATA.

000022          05  STOCK-DESCRIPTION-1          PIC X(53).

000023          05  STOCK-DESCRIPTION-2          PIC X(53).

000024          05  STOCK-DESCRIPTION-3          PIC X(53).

000025          05  STOCK-HELD                   PIC 9(06).

000026          05  STOCK-COST                   PIC 9(06)V99.

000027

000028  FD  STOCK-FILE-NEW.

000029  01  STOCK-RECORD-NEW.

000030      03  STOCK-KEY-NEW                    PIC 9(06).

000031      03  STOCK-DATA.

000032          05  STOCK-DESCRIPTION-1          PIC X(53).

000033          05  STOCK-DESCRIPTION-2          PIC X(53).

000034          05  STOCK-DESCRIPTION-3          PIC X(53).

000035          05  STOCK-HELD                   PIC 9(06).

000036          05  STOCK-COST                   PIC 9(06)V99.

000037

000038  WORKING-STORAGE SECTION.

000039  01 COUNT-WS PIC 9(8) VALUE ZERO.

000040  01 DONE-CHAR PIC X VALUE  "N".

000041          88 DONE VALUE "Y".

000042  PROCEDURE DIVISION.

000043  OPEN INPUT STOCK-FILE-OLD, OUTPUT STOCK-FILE-NEW

000044  READ STOCK-FILE-OLD NEXT

000045          AT END MOVE "Y" TO DONE-CHAR

000046  END-READ

000047  PERFORM UNTIL DONE

000048          MOVE STOCK-RECORD-OLD TO STOCK-RECORD-NEW

000049          WRITE STOCK-RECORD-NEW

000050          ADD 1 TO COUNT-WS

000051          READ STOCK-FILE-OLD NEXT

000052                  AT END MOVE "Y" TO DONE-CHAR

000053  END-PERFORM

000054  DISPLAY "    COUNT = ", COUNT-WS.

000055  STOP RUN.

Note that, at the beginning (lines 1 thru 3), we can specify IDXFORMAT and data and key compression if we like.  These settings have no affect on the input file -- they affect only the properties of the output file.  The settings are not required; they are included here just as an example.  By setting them, we can "convert" the old file into something new by giving the output file some new characteristics if we like.

The first step to writing such a program is to obtain the SELECT and FD for the file in question.  Next, make a copy of the SELECT and FD and change the name of the overall record name, the record key, and alternate key fields (if any), by appending "OLD" to the old version and "NEW" to the new.  In this example the file does not contain alternate keys, but if it did, their names would have to be qualified with "OLD" and "NEW" for uniqueness.

It is not necessary to change the name of every field in the FD; it is only necessary to change the overall record name, the record key, and the alternate key fields (if any).  The other fields can maintain the same names because they are never explicitly referred to; at line 48, the entire record is moved at once from old to new.

Note that the program does not declare a FILE-STATUS data item, and does not check the file status after each I-O operation.  This is an efficient approach, because in the absence of a file-status item, if any serious I-O error happens to occur, the runtime system takes it upon itself to automatically stop the program and put out a meaningful error including an explanatory text message.