Sometimes you need to make some small changes in the contents of a file. Of course it possible to create a brand new file with the new, modified contents but this is not practical. COBOL provides you with an OPEN I-O mode with which you can modify only the required record in a file.
In other words, there is another file opening mode; the I-O mode; and another special REWRITE statement. Suppose that you want to change the surname field of the 20th record of a seq file (originally "AYFER") into "AYFEROGLU".
The program that you can write could read like
SELECT MYFILE ASSIGN TO DISK "MYFILE.DAT"
ORGANIZATION IS SEQUENTIAL.
....
FD MYFILE.
01 MYFILE-REC.
02 M-NAME PIC X(16).
02 M-SURNAME PIC X(16).
02 M-BIRTHDATE.
03 M-BD-YEAR PIC 9999.
03 M-BD-MONTH PIC 99.
03 M-BD-DAY PIC 99.
PROCEDURE DIVISION.
....
OPEN I-O MYFILE.
....
MOVE 20 TO N.
....
PERFORM READ-A-REC N-1 TIMES.
*
* TO MAKE SURE THAT WE ARE ON THE CORRECT RECORD
*
IF M-SURNAME NOT = "AYFER" DISPLAY "WRONG RECORD"
DISPLAY "RECORD NOT UPDATED"
CLOSE MYFILE
STOP RUN.
MOVE "AYFEROGLU" TO M-SURNAME.
REWRITE MYFILE-REC.
.....
CLOSE MYFILE.
....
In other words, there is another file opening mode; the I-O mode; and another special REWRITE statement. Suppose that you want to change the surname field of the 20th record of a seq file (originally "AYFER") into "AYFEROGLU".
The program that you can write could read like
SELECT MYFILE ASSIGN TO DISK "MYFILE.DAT"
ORGANIZATION IS SEQUENTIAL.
....
FD MYFILE.
01 MYFILE-REC.
02 M-NAME PIC X(16).
02 M-SURNAME PIC X(16).
02 M-BIRTHDATE.
03 M-BD-YEAR PIC 9999.
03 M-BD-MONTH PIC 99.
03 M-BD-DAY PIC 99.
PROCEDURE DIVISION.
....
OPEN I-O MYFILE.
....
MOVE 20 TO N.
....
PERFORM READ-A-REC N-1 TIMES.
*
* TO MAKE SURE THAT WE ARE ON THE CORRECT RECORD
*
IF M-SURNAME NOT = "AYFER" DISPLAY "WRONG RECORD"
DISPLAY "RECORD NOT UPDATED"
CLOSE MYFILE
STOP RUN.
MOVE "AYFEROGLU" TO M-SURNAME.
REWRITE MYFILE-REC.
.....
CLOSE MYFILE.
....
