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File handling 2016

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TONY THOMAS

This document provides an overview of file handling in COBOL, including objectives, basic terminology, file organization and access methods, and file handling verbs. It discusses sequential file organization and processing, with examples of opening, reading from, and writing to sequential files using the OPEN, READ, and WRITE verbs. It explains how records are stored in files and accessed using buffers, and demonstrates sample code for creating a sequential file and reading/writing records.

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File handling 2016
Objectives of the Session (1) Introduction to File handling. (2) File ORGANIZATION and ACCESS methods. (3) File handling verbs. (4) Sequential File processing. (5) Demonstration of sample programs.
FILES  COBOL is generally used in situations where the volume of data to be processed is large.  TO STORE LARGE VOLUMES OF DATA AND RETRIEVE IT LATER IN PROGRAMMING  To store Values(data) permanently
Sequential files  Records can be accessed in the order of their appearance  Magnetic tape file  sequential  Disk file  sequential, random etc
Introduction to File processing Field - Field type and Field size. FIELD to describe an item of information we are recording about an object (e.g. StudentName, DateOfBirth, CourseCode).  Record Record-Size, Fixed length records and Variable length records. RECORD to describe the collection of fields which record information about an object (e.g. a StudentRecord is a collection of fields recording information about a student).  Basic Terminologies 01 StudentRecord. 02 regno pic 9999. 02 name pic x(20). 02 address pic x(20)
Files. File Master files, Transaction files, File organization and File access method. FILE to describe a collection of one or more occurrences (instances) of a record type (template).
 Record occurrence (i.e. the values of a record)  Record type (i.e. the structure of the record). Every record in a file has a different value but the same structure.
Files, Records, Fields. StudId StudName DateOfBirth 9723456 COUGHLAN 10091961 9724567 RYAN 31121976 9534118 COFFEY 23061964 9423458 O'BRIEN 03111979 9312876 SMITH 12121976 STUDENTS DATA DIVISION. FILE SECTION. FD StudentFile. 01 StudentDetails. 02 StudId PIC 9(7). 02 StudName PIC X(8). 02 DateOfBirth PIC X(8). occurrences Record Type (Template) (Structure)
Example REGNO NAME AGE KA101 JYOTHI 19 KA102 ANIRUDH 20 KA103 SRIDHAR 18 Field-1 File Field-2 Field-3 Record-1 Record-2 Record-3 STUDENT
FILE CHARACTERISTICS The task of file handling is the responsibility of the system software known as IOCS (Input- Output control system). Programmer  only specify file characteristics
Record Size: The size of the records may be chosen by the programmer. Records contain fixed and/or variables size records DATA DIVISION. FILE SECTION. FD StudentFile. 01 StudentDetails. 02 StudId PIC 9(7). 02 StudName PIC X(8). 02 DateOfBirth PIC X(8).
Block Size: •group a number of consecutive records to form a block •The number of records in a block is often called “blocking factors”. •The actual handling of blocks is transparent to the programmer  specify no. of records in a block •Advantage  saving of input output time Memory can be saved (inter record gap) •This memory space is known as the buffer.
Buffers:  In Modern computers  I-O operations independent of the CPU by means of the hardware  data channel.  Enable overlapping of I-O with other CPU operation  To take advantage of this situation --> more than one buffer for a file
Organization and Access Two important characteristics of files are – DATA ORGANIZATION – METHOD OF ACCESS
Data organization - refers to the way the records of the file are organized on the backing storage device. - COBOL recognizes three main file organizations; – Sequential- Records organized serially. – Relative - Relative record number based organization. – Indexed- Index based organization.
METHOD OF ACCESS  The method of access refers to the way in which records are accessed. (sequential and random) – A file with an organization of Indexed or Relative may still have its records accessed sequentially. – But records in a file with an organization of Sequential can not be accessed directly.
Sequential file organization  Simplest and least flexible of all types of file organizations.  Can only be accessed sequentially.  Records can be only added to the end of the file.  Does not provide means to insert or delete records.  Most storage efficient.
FILE-CONTROL paragraph for sequential files SELECT file-name ASSIGN TO hardware-name [ RESERVE integer-1 { AREA/AREAS} [ ORGANIZATION IS SEQUENTIAL ] [ ACCESS MODE IS SEQUENTIAL] [ FILE STATUS IS identifier ]. ORGANIZATION/ACCESS : •Optional •Default sequential organization and sequential access
RESERVE: • The number of buffers used for the file. •RESERVE 1 AREA means only one buffer is to be used •Optional  default two buffers FILE STATUS: VALUES-alphanumeric values. 00:-Successful completion 10:- At end condition 30:- Permanent error condition 34:-Boundary violation
STUDENTS The Select and Assign Clause. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT StudentFile ASSIGN TO DISK organization is sequential. DISK
FD entries for Fixed length records FD file-name [ RECORD CONTAINS integer-1 CHARACTERS ] [ BLOCK CONTAINS integer-2 { RECORDS, CHARACTERS }] [ LABEL { RECORD IS, RECORDS ARE } { STANDARD, OMITTED }] [VALUE OF implementor-name-1 IS {dataname-2, literal-2] [ DATA { RECORD IS, RECORDS ARE } identifier-1, identifier-2, . . . ].
BLOCK CONTAINS CLAUSE: •Integer –1 of the BLOCK CONTAINS clause specifies the block size either in terms of records or in terms of characters. •For example, BLOCK CONTAINS 50 RECORDS means that there are 50 records in the block. •If omitted -- > one record per block RECORDS CONTAINS CLAUSE: •This clause specifies the records size. •Integer-1 specifies the number of characters in a record. •The RECORD CONTAINS clause is used for documentary purposes only.
LABEL RECORD CLAUSE: This clause specifies whether or not the standard header and trailer labels should be present in the magnetic-tape files. Label Records clause for disk files should be specified with Standard VALUE OF CLAUSE: The VALUE OF clause is entirely implementation- dependent. In most compilers this clause is used to specify a file title. The clause in such cases has the form.
DATA RECORD CLAUSE: •This clause documents the record names defined for the file. •For example, DATA RECORDS ARE REC-1, REC- 2, REC-3 means that there are three different record descriptions following the FD entry in which this DATA RECORDS clause is used.
Example of file-description entries: FD FILE – A RECORD CONTAINS 130 CHARACTERS BLOCK CONTAINS 20 RECORDS DATA RECORD IS FIRST-RECORD LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS “MY-LIFE.txt”. 01 FIRST-RECORD PIC X(130).
Record Buffers IDENTIFICATION DIVISION. etc. ENVIRONMENT DIVISION. etc. DATA DIVISION. FILE SECTION. Program RecordBuffer Declaration STUDENTS DISK Record Instance To process all the records in an INPUT file each record instance must be copied (read) from the file into the record buffer when required
 To create an OUTPUT file containing data records each record must be placed in the record buffer and then transferred (written) to the file.
IDENTIFICATION DIVISION. PROGRAM-ID. FIRSTFILE1. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT OUTFILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. DATA DIVISION. FILE SECTION FD OUTFILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "OUT.TXT". 01 OUTREC. 02 REG PIC 9(5). 02 NAM PIC X(20). 02 ADDR PIC X(40). WORKING-STORAGE SECTION. 77 A PIC 999.
PROCEDURE DIVISION. MAINPARA. OPEN OUTPUT OUTFILE. ACCEPT REG. ACCEPT NAM. ACCEPT ADDR. WRITE OUTREC. CLOSE OUTFILE. OPEN INPUT OUTFILE. READ OUTFILE. CLOSE OUTFILE. STOP RUN. FD OUTFILE 01 OUTREC. 02 REG PIC 9(5). 02 NAM PIC X(20). 02 ADDR PIC X(40).
MAINPARA. DISPLAY "ENTER NUMBER OF RECORDS". ACCEPT N. OPEN OUTPUT OUTFILE. PERFORM ACCEPT-PARA N TIMES. CLOSE OUTFILE. OPEN INPUT OUTFILE. DISPLAY " THE RECORD DISPLAYED AFTER READING". PERFORM DISPLAY-PARA N TIMES. CLOSE OUTFILE. STOP RUN. ACCEPT-PARA. DISPLAY "ENTER THE VALUE FOR EMP RECORD". ACCEPT REG. ACCEPT NAM. ACCEPT ADDR. WRITE OUTREC. DISPLAY-PARA. READ OUTFILE. DISPLAY OUTREC.
File handling verbs  OPEN  READ  WRITE  REWRITE  CLOSE
COBOL file handling Verbs  OPEN Before your program can access the data in an input file or place data in an output file  program OPEN it.  READ The READ copies a record occurrence/instance from the file and places it in the record buffer.  WRITE The WRITE copies the record it finds in the record buffer to the file.  CLOSE You must ensure that (before terminating) your program closes all the files it has opened.
OPEN verb  Syntax OPEN {INPUT, OUTPUT, I-O, EXTEND} Filename-1 . . . OPEN MODE STATEMENT INPUT OUTPUT I-O EXTEND READ WRITE REWRITE
The READ verb  To process all the records in the file we have to transfer them, one record at a time, from the file to the buffer.  COBOL provides the READ verb for this purpose.
READ verb syntax  The InternalFilename specified must be a file that has been OPENed for INPUT.  The NEXT RECORD clause is optional and generally not used.     lockStatementBENDAT IdentifierINTO RECORDNEXTlenameInternalFiREAD
 Using INTO Identifier clause causes the data to be read into the record buffer and then copied from there to the specified Identifier in one operation. – When this option is used there will be two copies of the data. It is the equivalent of a READ followed by a MOVE.
Working of the READ statement STUD-REC 1 0 1 J Y O T H I 2 5B U REGNO NAME AGE 1 3 A H N 2B EOF 1 2 I H A 2B 0 R C A 0U 0 N T Y 2U A STUDENT PERFORM P1 UNTIL LAST = -1 . . . . P1. READ STUDFILE AT END MOVE -1 TO LAST
Working of the READ statement STUD-REC 1 0 1 J Y O T H I 2 5B U REGNO NAME AGE 1 3 A H N 2B EOF 1 2 I H A 2B 0 R C A 0U 0 N T Y 2U A STUDENT 1 0 1 J Y O T H I 2 5B U PERFORM P1 UNTIL LAST = -1 . . . . P1. READ STUDFILE AT END MOVE -1 TO LAST
Working of the READ statement 1 0 1 J Y O T H I 2 5B U REGNO NAME AGE 1 3 A H N 2B EOF 0 R C A 0U A 1 0 2 N I T H Y A 2 2B U 1 0 2 N I T H Y A 2 2B U PERFORM P1 UNTIL LAST = -1 . . . . P1. READ STUDFILE AT END MOVE -1 TO LAST STUD-REC STUDENT
Working of the READ statement 1 0 1 J Y O T H I 2 5B U REGNO NAME AGE EOF 1 0 3 R A C H A N 2 0B U 1 0 2 N I T H Y A 2 2B U A 1 0 3 R A C H A N 2 0B U A PERFORM P1 UNTIL LAST = -1 . . . . P1. READ STUDFILE AT END MOVE -1 TO LAST STUD-REC STUDENT
Working of the READ statement 1 0 1 J Y O T H I 2 5B U REGNO NAME AGE EOF J J J J J J J J J J JJ J 1 0 2 N I T H Y A 2 2B U J 1 0 3 R A C H A N 2 0B U A J J J J JJ JJ PERFORM P1 UNTIL LAST = -1 . . . . P1. READ STUDFILE AT END MOVE -1 TO LAST STUD-REC STUDENT
WRITE Syntax.  To WRITE data to a file move the data to the record buffer (declared in the FD entry) and then WRITE the contents of record buffer to the file.  WRITE ADVANCING AdvanceNum MnemonicName PAGE RecordName FROM Identifier BEFORE AFTER LINE LINES                                          
F r a n k C u r t a i n9 3 3 4 5 6 7 L M 0 5 1 StudentID StudentName Course. StudentRecord F r a n k C u r t a i n9 3 3 4 5 6 7 L M 0 5 1 EOF How the WRITE works OPEN OUTPUT StudentFile. MOVE "9334567Frank Curtain LM051" TO StudentDetails. WRITE StudentDetails. MOVE "9383715Thomas Healy LM068" TO StudentDetails. WRITE StudentDetails. CLOSE StudentFile. STOP RUN. Students
Working of the WRITE statement STUD-REC 1 0 1 J Y O T H I 2 5B U REGNO NAME AGE EOF 1 0 1 J Y O T H I 2 5U MOVE "BU101" TO REGNO MOVE "JYOTHI" TO NAME MOVE 25 TO AGE. WRITE STUD-REC. . B STUDENT 01 STUD-REC 02 REGNO PIC X(5). 02 NAME PIC X(15). 02 AGE PIC 99.
Working of the WRITE statement REGNO NAME AGE EOF 1 0 2 N I T H Y A 2 2B U 1 0 2 N I T H Y A 2 2B U 1 0 1 J Y O T H I 2 5UB STUD-REC STUDENT MOVE “BU101JYOTHI 25” TO STUD-REC. WRITE STUD-REC. MOVE “BU102NITHYA 22” TO STUD-REC. WRITE STUD-REC.
 To transfer a record from an input file to an output file we will have to – read the record into the input record buffer – transfer it to the output record buffer – write the data to the output file from the output record buffer
ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT OUTFILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. SELECT INFILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. DATA DIVISION. FILE SECTION FD INFILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "IN.TXT". 01 INREC. 02 REGNO PIC 9(5). 02 NAME PIC X(20). 02 ADDRESS PIC X(40). FD OUTFILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "FILEOUT.TXT". 01 OUTREC. 02 REG PIC 9(5). 02 FILLER PIC X(3). 02 NAM PIC X(20). 02 FILLER PIC X(3). 02 ADDR PIC X(40). WORKING-STORAGE SECTION. 77 LAST PIC S9 VALUE 0.
PROCEDURE DIVISION. MAINPARA. OPEN INPUT INFILE. OPEN OUTPUT OUTFILE. PERFORM READ-WRITE-PARA UNTIL LAST = -1. CLOSE INFILE, OUTFILE. STOP RUN. READ-WRITE-PARA. READ INFILE AT END MOVE -1 TO LAST. IF LAST NOT = -1 MOVE REGNO TO REG MOVE NAME TO NAM MOVE ADDRESS TO ADDR DISPLAY OUTREC WRITE OUTREC.
To search a record in a file - open the file - accept the value of record to find - perform the readpara until last = -1 - - in readpara - read each record at end move -1 to last - after reading check whether that record is the last record
WORKING-STORAGE SECTION. 77 SFLAG PIC 99 VALUE 0. 77 SNAME PIC X(20). 77 LAST PIC S9 VALUE 0. PROCEDURE DIVISION. MAINPARA. OPEN INPUT INFILE. DISPLAY "ENTER THE NAME TO SEARCH". ACCEPT SNAME. PERFORM READ-MODIFY-PARA UNTIL LAST = -1. IF SFLAG = 0 DISPLAY "NO RECORDS PRESENT". CLOSE INFILE. STOP RUN. READ-MODIFY-PARA. READ INFILE AT END MOVE -1 TO LAST. IF LAST NOT = -1 IF NAME = SNAME COMPUTE SFLAG = 1 DISPLAY "SEARCH FOUND". DISPLAY INREC.
REWRITE verb •REWRITE is used to update an existing record in the file Syntax REWRITE record-name [ FROM identifier-1 ] Note: •The REWRITE statement can only be used if the file is opened in the I-O mode and its execution must be preceded by the successful READ statement on the file. •The REWRITE statement replaces last read record
WORKING-STORAGE SECTION. 77 SFLAG PIC 99 VALUE 0. 77 SNAME PIC X(20). 77 LAST PIC S9 VALUE 0. PROCEDURE DIVISION. MAINPARA. OPEN I-O INFILE. DISPLAY "ENTER THE NAME TO SEARCH". ACCEPT SNAME. PERFORM READ-MODIFY-PARA UNTIL LAST = -1 OR SFLAG = 1. IF SFLAG = 1 PERFORM ACCEPT-PARA. IF SFLAG = 0 DISPLAY "NO RECORDS PRESENT". CLOSE INFILE. STOP RUN. READ-MODIFY-PARA. READ INFILE AT END MOVE -1 TO LAST. IF LAST NOT = -1 IF NAME = SNAME COMPUTE SFLAG = 1 DISPLAY "SEARCH FOUND" DISPLAY INREC. ACCEPT-PARA. DISPLAY "ENTER MODIFIED VALU ACCEPT REGNO. ACCEPT NAME. ACCEPT ADDRESS. REWRITE INREC.
CLOSE verb  Syntax CLOSE filename1  Releases the named files from the program.  If a file is stored on a magnetic tape, after the execution of the CLOSE statement the tape is rewound.  Is optional for COBOL- 85.
Sequential files - A Final Look Advantages Slow - when the hit rate is low. Complicated to change (insert, delete). Fast - when the hit rate is high. Most storage efficient. Simple organization. Dis-advantages
IDENTIFICATION DIVISION. PROGRAM-ID. S2. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT STU-FILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL ACCESS MODE IS SEQUENTIAL. DATA DIVISION. FILE SECTION. FD STU-FILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS “STU.DAT” DATA RECORD IS STU-REC. 01 STU-REC. 02 SNO PIC 9(2). 02 SNAME PIC X(10). WORKING-STORAGE SECTION. 01 ANS PIC X VALUE SPACE.
PROCEDURE DIVISION. P-1. DISPLAY(1 1) ERASE. OPEN EXTEND STU-FILE. PERFORM G-W-PARA UNTIL ANS = "N". CLOSE STU-FILE. STOP RUN. G-W-PARA. DISPLAY(1 1) ERASE. DISPLAY(3 5) "SNO : ". ACCEPT SNO. DISPLAY(5 5) "SNAME : ". ACCEPT SNAME. WRITE STU-REC. DISPLAY(10 5) "CONTINUE [ Y/ N ] : ". ACCEPT ANS.
IDENTIFICATION DIVISION. PROGRAM-ID. FILE1. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT OUTFILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. SELECT INFILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. DATA DIVISION. FILE SECTION FD INFILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "IN.TXT". 01 INREC. 02 REGNO PIC 9(5). 02 NAME PIC X(20). 02 ADDRESS PIC X(20).
FD OUTFILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "FILEOUT.TXT". 01 OUTREC PIC X(75).
WORKING-STORAGE SECTION. 01 HEAD-1. 02 FILLER PIC X(25). 02 FILLER PIC X(12) VALUE "ABC PVT Ltd". 01 LINE-1. 02 FILLER PIC X(24). 02 FILLER PIC X(14) VALUE ALL "-". 01 LINE-2. 02 FILLER PIC X(75) VALUE ALL "-". 01 HEAD-2. 02 FILLER PIC X(8) VALUE "EMPNO". 02 FILLER PIC X(23) VALUE "EMP NAME". 02 FILLER PIC X(20) VALUE "ADDRESS". 01 DETAILS. 02 REG PIC 9(5). 02 FILLER PIC X(3). 02 NAM PIC X(20). 02 FILLER PIC X(3). 02 ADDR PIC X(40). 77 LAST PIC S9 VALUE 0.
PROCEDURE DIVISION. MAINPARA. OPEN INPUT INFILE. OPEN OUTPUT OUTFILE. MOVE HEAD-1 TO OUTREC. WRITE OUTREC. MOVE LINE-1 TO OUTREC. WRITE OUTREC. MOVE LINE-2 TO OUTREC. WRITE OUTREC. MOVE HEAD-2 TO OUTREC. WRITE OUTREC. MOVE LINE-2 TO OUTREC. WRITE OUTREC.
PERFORM READ-WRITE-PARA UNTIL LAST = -1. MOVE LINE-2 TO OUTREC. WRITE OUTREC. CLOSE INFILE, OUTFILE. STOP RUN. READ-WRITE-PARA. READ INFILE AT END MOVE -1 TO LAST. IF LAST NOT = -1 MOVE REGNO TO REG MOVE NAME TO NAM MOVE ADDRESS TO ADDR MOVE DETAILS TO OUTREC WRITE OUTREC.
IDENTIFICATION DIVISION. PROGRAM-ID. S3. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT STU-FILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL ACCESS MODE IS SEQUENTIAL DATA DIVISION. FILE SECTION. FD STU-FILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS 'STU.DAT' DATA RECORD IS STU-REC. 01 STU-REC. 02 SNO PIC 9(2). 02 SNAME PIC X(10). WORKING-STORAGE SECTION. 01 N PIC 99.
PROCEDURE DIVISION. P-1. DISPLAY(1 1) ERASE. DISPLAY “ENTER THE NUMBER” ACCEPT N. OPEN OUTPUT STU-FILE. PERFORM G-W-PARA N TIMES. CLOSE STU-FILE. OPEN INPUT STU-FILE. PERFORM OUTPARA N TIMES CLOSE STU-FILE. STOP RUN. G-W-PARA. DISPLAY(1 1) ERASE. DISPLAY(3 5) "SNO : ". ACCEPT SNO. DISPLAY(5 5) "SNAME : ". ACCEPT SNAME. WRITE STU-REC. OUTPARA. READ STU-FILE. DISPLAY “SNO=“ SNO “ NAME=“ SNAME.
• The process of sequencing the records in some desired manner is known as sorting. • Sorting is done upon some key data item in the record. • Major key and minor key SORT VERB
• SORT verb can be used to sort a sequential file. • The MERGE verb can be used to merge several sorted files to create a new file containing the records of these files in the sorting order. • The sort verb have different forms. • The simple sort verb requires the three files • the unsorted input file • the sorted output file • the work file.
The format of thesimple SORT verb is as follows: Filename-1 is the name of the workfile Filename-2  input file name Filename-3  output file name Filename-2 and filename-3 should be specified through FD entry
The work file is to be defined by a sort description entry(SD entry). The format of SD entry is as follows.
The following rules (i) The input, output as well as the work file are open by the sort statement before the sorting begins and are closed by the sort statement itself after the sorting is over. (ii) There can be any number of SORT statement in a program. (iii) The sorting can be done on any number of keys.
(iv) All the keys on which the sorting is done, must appear with their description in the record description of file name1. (v) The SELECT clauses for the work file file- name-1 is SELECT file-name-1 ASSIGN TO hardware-name.
A file for which a record having 2 fields, namely: Account Number and Name is already available. Sort the file based on the ascending order of Account Number. IDENTIFICATION DIVISION. PROGRAM-ID. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT O1-FILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. SELECT S1-FILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. SELECT W-FILE ASSIGN TO DISK.
DATA DIVISION. FILE SECTION. FD O1-FILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "O1.DAT". 01 O1-REC. 02 O1-ACC-NO PIC 9(2). 02 O1-NAME PIC X(4). FD S1-FILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "S1.DAT". 01 S1-REC. 02 S1-ACC-NO PIC 9(2). 02 S1-NAME PIC X(4). SD W-FILE. 01 W-REC. 02 W-ACC-NO PIC 9(2). 02 W-NAME PIC X(4). Size of 3 files should be same No need to Specify all Fields in workfile
PROCEDURE DIVISION. P-1. SORT W-FILE ON ASCENDING KEY W-ACC-NO USING O1-FILE GIVING S1-FILE. STOP RUN.
SIMPLE MERGE VERB the merging of files is frequently required in various commercial application. It is possible to merge two or more files with one MERGE statement. The format of the simple MERGE verb is as follows.
The input files to be merged through the MERGE statement are specified in the USING phrase. These files must be sequential files and must be sorted on the merge keys. The rules of the SORT statement in respect of the ASCENDING/DECENDING KEY phrase are also applicable in this case. ALL THE FILES IN THE MERGE STATEMENT MUST HAVE RECORDS OF SAME SIZE AND THE POSITION OF THE MERGE KEY WITHIN THE RECORD DESCRIPTION OF EACH OF THE FILES MUST BE SAME
TWO FILES FOR WHICH A RECORD HAVING 2 FIELDS NAMELY ACCOUNT NUMBER AND NAME ARE ALREADY AVAILABLE. MERGE THESE TWO FILES AND CREATE A NEW FILE BASED ON THE ASCENDING ORDER OF ACCOUNT NUMBER. IDENTIFICATION DIVISION. PROGRAM-ID. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION.
FILE-CONTROL. SELECT O1-FILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. SELECT O2-FILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. . SELECT M-FILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. SELECT W-FILE ASSIGN TO DISK.
DATA DIVISION. FILE SECTION. FD O1-FILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "O1.DAT". 01 O1-REC. 02 O1-ACC-NO PIC 9(2). 02 O1-NAME PIC X(4). FD O2-FILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "O2.DAT". 01 O2-REC. 02 O2-ACC-NO PIC 9(2). 02 O2-NAME PIC X(4).
FD M-FILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "M.DAT". 01 M-REC. 02 M-ACC-NO PIC 9(2). 02 M-NAME PIC X(4). SD W-FILE. 01 W-REC. 02 W-ACC-NO PIC 9(2). 02 W-NAME PIC X(4).
PROCEDURE DIVISION. P-1. MERGE W-FILE ON ASCENDING KEY W-ACC-NO USING O1-FILE O2-FILE GIVING M-FILE. STOP RUN.
DIRECT ACCESS file • Files which are stored on a direct access storage medium such as a magnetic disk, are often called direct access files. • COBOL supports three different organization for disk files • Sequential • relative • and index sequential.
• A relative file is a magnetic-disk file organized in such a way that each record is identified by a relative record number. • The relative record number specifies the position of the record from the beginning of the file. • Thus the relative record number 1identifies the first record, the relative record number 2 identifies the second record and so on. • A relative file can be access either sequentially or randomly. RELATIVES file
• When the file is accessed sequentially the records are accessed in the increasing order of their relative record numbers. • When a file is accessed randomly, the programmer must specify the relative record number.
•In relative organization, the reading as well as the writing can be done randomly. •Thus when a file is created by writing the record randomly, some of the record position may remain empty. •While these positions can be filled in subsequently, the programmer should avoid specifying these empty positions while reading such as relative file randomly. •If a relative file is read in a sequential manner, such empty position within it, if any, are ignored.
The handling of relative files requires some special codes in the FILE-CONTROL paragraph as well as in the PROCEDURE DIVISION. FILE-CONTROL paragraph for relative files: The general format for the SELECT clause for a relative file is as follows.
ACCESS mode  Sequential Access mode  Random ACCESS MODE IS DYNAMIC  file is accessed sequentially or/and randomly in the Procedure Division The phrase RELATIVE KEY must be specified when access mode is RANDOM or DYNAMIC Dataname-1  called relative key data item  relative record number Programmer must place an appropriate value in the relative key data item  to access randomly Dataname-1  unsigned integer  must not be part of the record description for the said relative file
Whether the file should be used sequentially or randomly, should specified through the word SEQUENTIAL or RANDOM in the access mode clause the clause ACCESS MODE IS DYNAMIC it indicates that the file is accessed sequentially and / or randomly in the PROCEDURE DIVISION.
INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT REL-FILE ASSIGN TO DISK ORGANIZATION IS RELATIVE ACCESS MODE IS DYNAMIC RELATIVE KEY IS RK-NO. FILE SECTION FD REL-FILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "IN.TXT". 01 REL-REC. 02 REGNO PIC 9(5). 02 NAME PIC X(20). 02 ADDRESS PIC X(20). WORKING-STORAGE SECTION. 77 RK-NO PIC 999.
The statements OPEN,CLOSE, READ,WRITE and REWRITE which are available for sequential files are available for the relative files. In addition, two other words, namely, DELETE and START are also available. PROCEDURE DIVISION for relative files
READ STATEMENTS: •As usual, a READ statements reads a record of the file. •The file must be open in either the input or I-O mode. There are 3 different general format for the read statements
This format is the normal form of the READ statements. •Applicable to sequential file access
•Format 2 is used when the access mode is either random or dynamic. •Record to be read is identified from the value in the relative data item MOVE 50 TO REL-KEY. READ EMP-FILE RECORD INVALID KEY PERFORM NOT-FOUND-PARA
•Format 3 can be used when the Access mode is dynamic and the records are to be read sequentially. •The next record is identified according to the following rules: (i) When the READ NEXT statements is the first statement to be executed after the open statement on the file, the next record is the first record of the file. (ii) the execution of the READ NEXT statement follows the execution of the start statement  next record is the record logically positioned by the START statement
READ REL-FILE next record AT END MOVE -1 TO LAST. IF LAST NOT = -1 DISPLAY REL-REC.
WRITE Statement The WRITE statement for a relative file has the following format. The file must be open either in the OUTPUT or I-O mode. •File access is RANDOM  the statement releases the record to that relative record position  indicated by the REL-KEY •In sequential access records are released to the file in the sequential record position
The imperative statement of the INVALID KEY phrase is execution in the following case: (i) when an attempt is made to write beyond the externally-defined boundaries of the file. (ii) When an attempt is made to write in the record position which already contains a valid record
DISPLAY "ENTER THE DETAILS". ACCEPT REGNO. ACCEPT NAME. ACCEPT ADDRESS. COMPUTE RK-NO = REGNO. DISPLAY "ACCEPT THE VALUE OF RELKEY". ACCEPT RK-NO. WRITE REL-REC.
REWRITE STATEMENT: The REWRITE statement has the following format for a relative file, REWRITE record-name [ FROM identifier ] [ ; INVALID KEY imperative –statement ] • The REWRITE statement is used to replace an exiting record by the contents of the record specified in the record name. • The file must be opened in the I-O mode.
Access mode  SEQUENTIAL •prior to REWRITE a READ statement on the file should be successfully executed •No need to specify INVALID KEY option here The imperative statement after the INVALID KEY is executed when an attempt is made to replace a record position which is empty Access mode  RANDOM or DYNAMIC •the record to be replaced is identified by the contents of relative key data
DELETE STATEMENT: The format of the DELETE statement is as follows: DELETE file-name RECORD [ ; INVALID KEY imperative-statement ] •The file must be opened in I-O mode • ACCESS MODE IS SEQUENTIAL •the execution of the DELETE statement must be preceded by the execution of a READ statement on the file and the INVALID KEY phrase should not be specified. INVALID KEY  when an attempt is made to delete the record of an empty record position
START STATEMENT: The format of the START statement is as follows: START file-name KEY IS = DATANAME1 > NOT < [ ; INVALID KEY imperative-statement ] •The START statement enable the programmer to position the relative file at some specified point •ie subsequent sequential operation on this file can start from this point. Open in INPUT or I-O mode
INDEXED SEQUENTIAL FILES Relative files  based on relative key To overcome this problem ie to identify the records based on value in the record field  index sequential file
INDEXED SEQUENTIAL FILES •In indexed sequential files (also referred to as indexed files), the records are stored in the key sequence order (ascending order). •In addition, some index tables are also created and maintained with the file. •An indexed file on COBOL can be accessed either sequential or randomly. •While creating an indexed file the records can be written only sequentially and in the ascending order of the key.
•When an indexed file is accessed randomly, the sequence in which the records are accessed is controlled by the programmer by specifying the value of a data item called record key. •Indexed files in a COBOL program can be handled through suitable special codes in the FILE-CONTROL paragraph and in the PROCEDURE DIVISION.
FILE-CONTROL paragraph for indexed files The general format for the SELECT clause for an files is as follows:
The ORGANIZATION clause indicates that the file is an indexed file. The RECORD KEY clause specifies the record key data item on the basis of which the file is sequenced. (prime key) The dataname-1 must be an alphanumeric field within the record description for the file Alternate key  must be defined in the record description
•Two or more records having the same value for the prime key are not allowed •Duplicates are allowed for alternative keys •Records of an indexed file can be accessed by specifying the primary key or alternative key
READ STATEMENT When access mode is RANDOM or DYNAMIC  the records are to be read in a random manner, READ file-name RECORD [ INTO IDENTIFIER ] [ ; KEY IS data-name ] [ ; INVALID KEY imperative-statement ] •The data name in the KEY IS phrase must be either the prime key or the alternative key item. •If the phrase is not specified, the prime key is assumed. MOVE “1234” TO EMPNO. READ EMP-FILE REOCRD KEY IS EMP-NO INVALID KEY PERFORM NOT-FOUND-PARA
ACCESS MODE IS SEQUENTIAL OR DYNAMIC  SAME SYNTAX OF RELATIVE FILE
WRITE STATEMENT •The records are written to be logical position as determined from the value of the record key. •OUTPUT MODE  the records must be released in the ascending order of the record key values regardless of the ACCESS mode •Records can be released in any order only when the file is opened in I-O mode and Access mode is RANDOM OR DYNAMIC
The INVALID KEY condition arises in the following cases: (i) Attempt to write a record beyond the externally defined boundaries of the file. (ii) file is opened in the OUTPUT mode and the value of the record key is not greater than the value of the record key for the previous record written. (iii) When the value of the record key is equal to the record key of a record key already present in the file.
REWRITE STATEMENT •File must be opened in the I-O mode, •If SEQENTIAL access mode the value of the record key of the record being replaced must be equal to that of the record last read from this file. The INVALID KEY condition arises (i) when the record key does not match that of an existing record in the file. (ii) For SEQUENTIAL access, when the value of the record key is not identical to that of the last record read from the file.
DELETE STATEMENT •Open  I-O mode •If the access is SEQUENTIAL, the INVALID KEY phrase should not be specified •Before executing DELETE there must be successful READ statement. •For RANDOM or DYNAMIC  record to be deleted is determined by the value of record key •INVALID KEY phrase should be specified
START Position the file to the first logical record Access mode  SEQUENTIAL or DYNAMIC File opened  I-O or INPUT

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File handling 2016

  • 2. Objectives of the Session (1) Introduction to File handling. (2) File ORGANIZATION and ACCESS methods. (3) File handling verbs. (4) Sequential File processing. (5) Demonstration of sample programs.
  • 3. FILES  COBOL is generally used in situations where the volume of data to be processed is large.  TO STORE LARGE VOLUMES OF DATA AND RETRIEVE IT LATER IN PROGRAMMING  To store Values(data) permanently
  • 4. Sequential files  Records can be accessed in the order of their appearance  Magnetic tape file  sequential  Disk file  sequential, random etc
  • 5. Introduction to File processing Field - Field type and Field size. FIELD to describe an item of information we are recording about an object (e.g. StudentName, DateOfBirth, CourseCode).  Record Record-Size, Fixed length records and Variable length records. RECORD to describe the collection of fields which record information about an object (e.g. a StudentRecord is a collection of fields recording information about a student).  Basic Terminologies 01 StudentRecord. 02 regno pic 9999. 02 name pic x(20). 02 address pic x(20)
  • 6. Files. File Master files, Transaction files, File organization and File access method. FILE to describe a collection of one or more occurrences (instances) of a record type (template).
  • 7.  Record occurrence (i.e. the values of a record)  Record type (i.e. the structure of the record). Every record in a file has a different value but the same structure.
  • 8. Files, Records, Fields. StudId StudName DateOfBirth 9723456 COUGHLAN 10091961 9724567 RYAN 31121976 9534118 COFFEY 23061964 9423458 O'BRIEN 03111979 9312876 SMITH 12121976 STUDENTS DATA DIVISION. FILE SECTION. FD StudentFile. 01 StudentDetails. 02 StudId PIC 9(7). 02 StudName PIC X(8). 02 DateOfBirth PIC X(8). occurrences Record Type (Template) (Structure)
  • 9. Example REGNO NAME AGE KA101 JYOTHI 19 KA102 ANIRUDH 20 KA103 SRIDHAR 18 Field-1 File Field-2 Field-3 Record-1 Record-2 Record-3 STUDENT
  • 10. FILE CHARACTERISTICS The task of file handling is the responsibility of the system software known as IOCS (Input- Output control system). Programmer  only specify file characteristics
  • 11. Record Size: The size of the records may be chosen by the programmer. Records contain fixed and/or variables size records DATA DIVISION. FILE SECTION. FD StudentFile. 01 StudentDetails. 02 StudId PIC 9(7). 02 StudName PIC X(8). 02 DateOfBirth PIC X(8).
  • 12. Block Size: •group a number of consecutive records to form a block •The number of records in a block is often called “blocking factors”. •The actual handling of blocks is transparent to the programmer  specify no. of records in a block •Advantage  saving of input output time Memory can be saved (inter record gap) •This memory space is known as the buffer.
  • 13. Buffers:  In Modern computers  I-O operations independent of the CPU by means of the hardware  data channel.  Enable overlapping of I-O with other CPU operation  To take advantage of this situation --> more than one buffer for a file
  • 14. Organization and Access Two important characteristics of files are – DATA ORGANIZATION – METHOD OF ACCESS
  • 15. Data organization - refers to the way the records of the file are organized on the backing storage device. - COBOL recognizes three main file organizations; – Sequential- Records organized serially. – Relative - Relative record number based organization. – Indexed- Index based organization.
  • 16. METHOD OF ACCESS  The method of access refers to the way in which records are accessed. (sequential and random) – A file with an organization of Indexed or Relative may still have its records accessed sequentially. – But records in a file with an organization of Sequential can not be accessed directly.
  • 17. Sequential file organization  Simplest and least flexible of all types of file organizations.  Can only be accessed sequentially.  Records can be only added to the end of the file.  Does not provide means to insert or delete records.  Most storage efficient.
  • 18. FILE-CONTROL paragraph for sequential files SELECT file-name ASSIGN TO hardware-name [ RESERVE integer-1 { AREA/AREAS} [ ORGANIZATION IS SEQUENTIAL ] [ ACCESS MODE IS SEQUENTIAL] [ FILE STATUS IS identifier ]. ORGANIZATION/ACCESS : •Optional •Default sequential organization and sequential access
  • 19. RESERVE: • The number of buffers used for the file. •RESERVE 1 AREA means only one buffer is to be used •Optional  default two buffers FILE STATUS: VALUES-alphanumeric values. 00:-Successful completion 10:- At end condition 30:- Permanent error condition 34:-Boundary violation
  • 20. STUDENTS The Select and Assign Clause. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT StudentFile ASSIGN TO DISK organization is sequential. DISK
  • 21. FD entries for Fixed length records FD file-name [ RECORD CONTAINS integer-1 CHARACTERS ] [ BLOCK CONTAINS integer-2 { RECORDS, CHARACTERS }] [ LABEL { RECORD IS, RECORDS ARE } { STANDARD, OMITTED }] [VALUE OF implementor-name-1 IS {dataname-2, literal-2] [ DATA { RECORD IS, RECORDS ARE } identifier-1, identifier-2, . . . ].
  • 22. BLOCK CONTAINS CLAUSE: •Integer –1 of the BLOCK CONTAINS clause specifies the block size either in terms of records or in terms of characters. •For example, BLOCK CONTAINS 50 RECORDS means that there are 50 records in the block. •If omitted -- > one record per block RECORDS CONTAINS CLAUSE: •This clause specifies the records size. •Integer-1 specifies the number of characters in a record. •The RECORD CONTAINS clause is used for documentary purposes only.
  • 23. LABEL RECORD CLAUSE: This clause specifies whether or not the standard header and trailer labels should be present in the magnetic-tape files. Label Records clause for disk files should be specified with Standard VALUE OF CLAUSE: The VALUE OF clause is entirely implementation- dependent. In most compilers this clause is used to specify a file title. The clause in such cases has the form.
  • 24. DATA RECORD CLAUSE: •This clause documents the record names defined for the file. •For example, DATA RECORDS ARE REC-1, REC- 2, REC-3 means that there are three different record descriptions following the FD entry in which this DATA RECORDS clause is used.
  • 25. Example of file-description entries: FD FILE – A RECORD CONTAINS 130 CHARACTERS BLOCK CONTAINS 20 RECORDS DATA RECORD IS FIRST-RECORD LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS “MY-LIFE.txt”. 01 FIRST-RECORD PIC X(130).
  • 26. Record Buffers IDENTIFICATION DIVISION. etc. ENVIRONMENT DIVISION. etc. DATA DIVISION. FILE SECTION. Program RecordBuffer Declaration STUDENTS DISK Record Instance To process all the records in an INPUT file each record instance must be copied (read) from the file into the record buffer when required
  • 27.  To create an OUTPUT file containing data records each record must be placed in the record buffer and then transferred (written) to the file.
  • 28. IDENTIFICATION DIVISION. PROGRAM-ID. FIRSTFILE1. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT OUTFILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. DATA DIVISION. FILE SECTION FD OUTFILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "OUT.TXT". 01 OUTREC. 02 REG PIC 9(5). 02 NAM PIC X(20). 02 ADDR PIC X(40). WORKING-STORAGE SECTION. 77 A PIC 999.
  • 29. PROCEDURE DIVISION. MAINPARA. OPEN OUTPUT OUTFILE. ACCEPT REG. ACCEPT NAM. ACCEPT ADDR. WRITE OUTREC. CLOSE OUTFILE. OPEN INPUT OUTFILE. READ OUTFILE. CLOSE OUTFILE. STOP RUN. FD OUTFILE 01 OUTREC. 02 REG PIC 9(5). 02 NAM PIC X(20). 02 ADDR PIC X(40).
  • 30. MAINPARA. DISPLAY "ENTER NUMBER OF RECORDS". ACCEPT N. OPEN OUTPUT OUTFILE. PERFORM ACCEPT-PARA N TIMES. CLOSE OUTFILE. OPEN INPUT OUTFILE. DISPLAY " THE RECORD DISPLAYED AFTER READING". PERFORM DISPLAY-PARA N TIMES. CLOSE OUTFILE. STOP RUN. ACCEPT-PARA. DISPLAY "ENTER THE VALUE FOR EMP RECORD". ACCEPT REG. ACCEPT NAM. ACCEPT ADDR. WRITE OUTREC. DISPLAY-PARA. READ OUTFILE. DISPLAY OUTREC.
  • 31. File handling verbs  OPEN  READ  WRITE  REWRITE  CLOSE
  • 32. COBOL file handling Verbs  OPEN Before your program can access the data in an input file or place data in an output file  program OPEN it.  READ The READ copies a record occurrence/instance from the file and places it in the record buffer.  WRITE The WRITE copies the record it finds in the record buffer to the file.  CLOSE You must ensure that (before terminating) your program closes all the files it has opened.
  • 33. OPEN verb  Syntax OPEN {INPUT, OUTPUT, I-O, EXTEND} Filename-1 . . . OPEN MODE STATEMENT INPUT OUTPUT I-O EXTEND READ WRITE REWRITE
  • 34. The READ verb  To process all the records in the file we have to transfer them, one record at a time, from the file to the buffer.  COBOL provides the READ verb for this purpose.
  • 35. READ verb syntax  The InternalFilename specified must be a file that has been OPENed for INPUT.  The NEXT RECORD clause is optional and generally not used.     lockStatementBENDAT IdentifierINTO RECORDNEXTlenameInternalFiREAD
  • 36.  Using INTO Identifier clause causes the data to be read into the record buffer and then copied from there to the specified Identifier in one operation. – When this option is used there will be two copies of the data. It is the equivalent of a READ followed by a MOVE.
  • 37. Working of the READ statement STUD-REC 1 0 1 J Y O T H I 2 5B U REGNO NAME AGE 1 3 A H N 2B EOF 1 2 I H A 2B 0 R C A 0U 0 N T Y 2U A STUDENT PERFORM P1 UNTIL LAST = -1 . . . . P1. READ STUDFILE AT END MOVE -1 TO LAST
  • 38. Working of the READ statement STUD-REC 1 0 1 J Y O T H I 2 5B U REGNO NAME AGE 1 3 A H N 2B EOF 1 2 I H A 2B 0 R C A 0U 0 N T Y 2U A STUDENT 1 0 1 J Y O T H I 2 5B U PERFORM P1 UNTIL LAST = -1 . . . . P1. READ STUDFILE AT END MOVE -1 TO LAST
  • 39. Working of the READ statement 1 0 1 J Y O T H I 2 5B U REGNO NAME AGE 1 3 A H N 2B EOF 0 R C A 0U A 1 0 2 N I T H Y A 2 2B U 1 0 2 N I T H Y A 2 2B U PERFORM P1 UNTIL LAST = -1 . . . . P1. READ STUDFILE AT END MOVE -1 TO LAST STUD-REC STUDENT
  • 40. Working of the READ statement 1 0 1 J Y O T H I 2 5B U REGNO NAME AGE EOF 1 0 3 R A C H A N 2 0B U 1 0 2 N I T H Y A 2 2B U A 1 0 3 R A C H A N 2 0B U A PERFORM P1 UNTIL LAST = -1 . . . . P1. READ STUDFILE AT END MOVE -1 TO LAST STUD-REC STUDENT
  • 41. Working of the READ statement 1 0 1 J Y O T H I 2 5B U REGNO NAME AGE EOF J J J J J J J J J J JJ J 1 0 2 N I T H Y A 2 2B U J 1 0 3 R A C H A N 2 0B U A J J J J JJ JJ PERFORM P1 UNTIL LAST = -1 . . . . P1. READ STUDFILE AT END MOVE -1 TO LAST STUD-REC STUDENT
  • 42. WRITE Syntax.  To WRITE data to a file move the data to the record buffer (declared in the FD entry) and then WRITE the contents of record buffer to the file.  WRITE ADVANCING AdvanceNum MnemonicName PAGE RecordName FROM Identifier BEFORE AFTER LINE LINES                                          
  • 43. F r a n k C u r t a i n9 3 3 4 5 6 7 L M 0 5 1 StudentID StudentName Course. StudentRecord F r a n k C u r t a i n9 3 3 4 5 6 7 L M 0 5 1 EOF How the WRITE works OPEN OUTPUT StudentFile. MOVE "9334567Frank Curtain LM051" TO StudentDetails. WRITE StudentDetails. MOVE "9383715Thomas Healy LM068" TO StudentDetails. WRITE StudentDetails. CLOSE StudentFile. STOP RUN. Students
  • 44. Working of the WRITE statement STUD-REC 1 0 1 J Y O T H I 2 5B U REGNO NAME AGE EOF 1 0 1 J Y O T H I 2 5U MOVE "BU101" TO REGNO MOVE "JYOTHI" TO NAME MOVE 25 TO AGE. WRITE STUD-REC. . B STUDENT 01 STUD-REC 02 REGNO PIC X(5). 02 NAME PIC X(15). 02 AGE PIC 99.
  • 45. Working of the WRITE statement REGNO NAME AGE EOF 1 0 2 N I T H Y A 2 2B U 1 0 2 N I T H Y A 2 2B U 1 0 1 J Y O T H I 2 5UB STUD-REC STUDENT MOVE “BU101JYOTHI 25” TO STUD-REC. WRITE STUD-REC. MOVE “BU102NITHYA 22” TO STUD-REC. WRITE STUD-REC.
  • 46.  To transfer a record from an input file to an output file we will have to – read the record into the input record buffer – transfer it to the output record buffer – write the data to the output file from the output record buffer
  • 47. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT OUTFILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. SELECT INFILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. DATA DIVISION. FILE SECTION FD INFILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "IN.TXT". 01 INREC. 02 REGNO PIC 9(5). 02 NAME PIC X(20). 02 ADDRESS PIC X(40). FD OUTFILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "FILEOUT.TXT". 01 OUTREC. 02 REG PIC 9(5). 02 FILLER PIC X(3). 02 NAM PIC X(20). 02 FILLER PIC X(3). 02 ADDR PIC X(40). WORKING-STORAGE SECTION. 77 LAST PIC S9 VALUE 0.
  • 48. PROCEDURE DIVISION. MAINPARA. OPEN INPUT INFILE. OPEN OUTPUT OUTFILE. PERFORM READ-WRITE-PARA UNTIL LAST = -1. CLOSE INFILE, OUTFILE. STOP RUN. READ-WRITE-PARA. READ INFILE AT END MOVE -1 TO LAST. IF LAST NOT = -1 MOVE REGNO TO REG MOVE NAME TO NAM MOVE ADDRESS TO ADDR DISPLAY OUTREC WRITE OUTREC.
  • 49. To search a record in a file - open the file - accept the value of record to find - perform the readpara until last = -1 - - in readpara - read each record at end move -1 to last - after reading check whether that record is the last record
  • 50. WORKING-STORAGE SECTION. 77 SFLAG PIC 99 VALUE 0. 77 SNAME PIC X(20). 77 LAST PIC S9 VALUE 0. PROCEDURE DIVISION. MAINPARA. OPEN INPUT INFILE. DISPLAY "ENTER THE NAME TO SEARCH". ACCEPT SNAME. PERFORM READ-MODIFY-PARA UNTIL LAST = -1. IF SFLAG = 0 DISPLAY "NO RECORDS PRESENT". CLOSE INFILE. STOP RUN. READ-MODIFY-PARA. READ INFILE AT END MOVE -1 TO LAST. IF LAST NOT = -1 IF NAME = SNAME COMPUTE SFLAG = 1 DISPLAY "SEARCH FOUND". DISPLAY INREC.
  • 51. REWRITE verb •REWRITE is used to update an existing record in the file Syntax REWRITE record-name [ FROM identifier-1 ] Note: •The REWRITE statement can only be used if the file is opened in the I-O mode and its execution must be preceded by the successful READ statement on the file. •The REWRITE statement replaces last read record
  • 52. WORKING-STORAGE SECTION. 77 SFLAG PIC 99 VALUE 0. 77 SNAME PIC X(20). 77 LAST PIC S9 VALUE 0. PROCEDURE DIVISION. MAINPARA. OPEN I-O INFILE. DISPLAY "ENTER THE NAME TO SEARCH". ACCEPT SNAME. PERFORM READ-MODIFY-PARA UNTIL LAST = -1 OR SFLAG = 1. IF SFLAG = 1 PERFORM ACCEPT-PARA. IF SFLAG = 0 DISPLAY "NO RECORDS PRESENT". CLOSE INFILE. STOP RUN. READ-MODIFY-PARA. READ INFILE AT END MOVE -1 TO LAST. IF LAST NOT = -1 IF NAME = SNAME COMPUTE SFLAG = 1 DISPLAY "SEARCH FOUND" DISPLAY INREC. ACCEPT-PARA. DISPLAY "ENTER MODIFIED VALU ACCEPT REGNO. ACCEPT NAME. ACCEPT ADDRESS. REWRITE INREC.
  • 53. CLOSE verb  Syntax CLOSE filename1  Releases the named files from the program.  If a file is stored on a magnetic tape, after the execution of the CLOSE statement the tape is rewound.  Is optional for COBOL- 85.
  • 54. Sequential files - A Final Look Advantages Slow - when the hit rate is low. Complicated to change (insert, delete). Fast - when the hit rate is high. Most storage efficient. Simple organization. Dis-advantages
  • 55. IDENTIFICATION DIVISION. PROGRAM-ID. S2. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT STU-FILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL ACCESS MODE IS SEQUENTIAL. DATA DIVISION. FILE SECTION. FD STU-FILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS “STU.DAT” DATA RECORD IS STU-REC. 01 STU-REC. 02 SNO PIC 9(2). 02 SNAME PIC X(10). WORKING-STORAGE SECTION. 01 ANS PIC X VALUE SPACE.
  • 56. PROCEDURE DIVISION. P-1. DISPLAY(1 1) ERASE. OPEN EXTEND STU-FILE. PERFORM G-W-PARA UNTIL ANS = "N". CLOSE STU-FILE. STOP RUN. G-W-PARA. DISPLAY(1 1) ERASE. DISPLAY(3 5) "SNO : ". ACCEPT SNO. DISPLAY(5 5) "SNAME : ". ACCEPT SNAME. WRITE STU-REC. DISPLAY(10 5) "CONTINUE [ Y/ N ] : ". ACCEPT ANS.
  • 57. IDENTIFICATION DIVISION. PROGRAM-ID. FILE1. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT OUTFILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. SELECT INFILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. DATA DIVISION. FILE SECTION FD INFILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "IN.TXT". 01 INREC. 02 REGNO PIC 9(5). 02 NAME PIC X(20). 02 ADDRESS PIC X(20).
  • 58. FD OUTFILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "FILEOUT.TXT". 01 OUTREC PIC X(75).
  • 59. WORKING-STORAGE SECTION. 01 HEAD-1. 02 FILLER PIC X(25). 02 FILLER PIC X(12) VALUE "ABC PVT Ltd". 01 LINE-1. 02 FILLER PIC X(24). 02 FILLER PIC X(14) VALUE ALL "-". 01 LINE-2. 02 FILLER PIC X(75) VALUE ALL "-". 01 HEAD-2. 02 FILLER PIC X(8) VALUE "EMPNO". 02 FILLER PIC X(23) VALUE "EMP NAME". 02 FILLER PIC X(20) VALUE "ADDRESS". 01 DETAILS. 02 REG PIC 9(5). 02 FILLER PIC X(3). 02 NAM PIC X(20). 02 FILLER PIC X(3). 02 ADDR PIC X(40). 77 LAST PIC S9 VALUE 0.
  • 60. PROCEDURE DIVISION. MAINPARA. OPEN INPUT INFILE. OPEN OUTPUT OUTFILE. MOVE HEAD-1 TO OUTREC. WRITE OUTREC. MOVE LINE-1 TO OUTREC. WRITE OUTREC. MOVE LINE-2 TO OUTREC. WRITE OUTREC. MOVE HEAD-2 TO OUTREC. WRITE OUTREC. MOVE LINE-2 TO OUTREC. WRITE OUTREC.
  • 61. PERFORM READ-WRITE-PARA UNTIL LAST = -1. MOVE LINE-2 TO OUTREC. WRITE OUTREC. CLOSE INFILE, OUTFILE. STOP RUN. READ-WRITE-PARA. READ INFILE AT END MOVE -1 TO LAST. IF LAST NOT = -1 MOVE REGNO TO REG MOVE NAME TO NAM MOVE ADDRESS TO ADDR MOVE DETAILS TO OUTREC WRITE OUTREC.
  • 62. IDENTIFICATION DIVISION. PROGRAM-ID. S3. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT STU-FILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL ACCESS MODE IS SEQUENTIAL DATA DIVISION. FILE SECTION. FD STU-FILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS 'STU.DAT' DATA RECORD IS STU-REC. 01 STU-REC. 02 SNO PIC 9(2). 02 SNAME PIC X(10). WORKING-STORAGE SECTION. 01 N PIC 99.
  • 63. PROCEDURE DIVISION. P-1. DISPLAY(1 1) ERASE. DISPLAY “ENTER THE NUMBER” ACCEPT N. OPEN OUTPUT STU-FILE. PERFORM G-W-PARA N TIMES. CLOSE STU-FILE. OPEN INPUT STU-FILE. PERFORM OUTPARA N TIMES CLOSE STU-FILE. STOP RUN. G-W-PARA. DISPLAY(1 1) ERASE. DISPLAY(3 5) "SNO : ". ACCEPT SNO. DISPLAY(5 5) "SNAME : ". ACCEPT SNAME. WRITE STU-REC. OUTPARA. READ STU-FILE. DISPLAY “SNO=“ SNO “ NAME=“ SNAME.
  • 64. • The process of sequencing the records in some desired manner is known as sorting. • Sorting is done upon some key data item in the record. • Major key and minor key SORT VERB
  • 65. • SORT verb can be used to sort a sequential file. • The MERGE verb can be used to merge several sorted files to create a new file containing the records of these files in the sorting order. • The sort verb have different forms. • The simple sort verb requires the three files • the unsorted input file • the sorted output file • the work file.
  • 66. The format of thesimple SORT verb is as follows: Filename-1 is the name of the workfile Filename-2  input file name Filename-3  output file name Filename-2 and filename-3 should be specified through FD entry
  • 67. The work file is to be defined by a sort description entry(SD entry). The format of SD entry is as follows.
  • 68. The following rules (i) The input, output as well as the work file are open by the sort statement before the sorting begins and are closed by the sort statement itself after the sorting is over. (ii) There can be any number of SORT statement in a program. (iii) The sorting can be done on any number of keys.
  • 69. (iv) All the keys on which the sorting is done, must appear with their description in the record description of file name1. (v) The SELECT clauses for the work file file- name-1 is SELECT file-name-1 ASSIGN TO hardware-name.
  • 70. A file for which a record having 2 fields, namely: Account Number and Name is already available. Sort the file based on the ascending order of Account Number. IDENTIFICATION DIVISION. PROGRAM-ID. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT O1-FILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. SELECT S1-FILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. SELECT W-FILE ASSIGN TO DISK.
  • 71. DATA DIVISION. FILE SECTION. FD O1-FILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "O1.DAT". 01 O1-REC. 02 O1-ACC-NO PIC 9(2). 02 O1-NAME PIC X(4). FD S1-FILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "S1.DAT". 01 S1-REC. 02 S1-ACC-NO PIC 9(2). 02 S1-NAME PIC X(4). SD W-FILE. 01 W-REC. 02 W-ACC-NO PIC 9(2). 02 W-NAME PIC X(4). Size of 3 files should be same No need to Specify all Fields in workfile
  • 72. PROCEDURE DIVISION. P-1. SORT W-FILE ON ASCENDING KEY W-ACC-NO USING O1-FILE GIVING S1-FILE. STOP RUN.
  • 73. SIMPLE MERGE VERB the merging of files is frequently required in various commercial application. It is possible to merge two or more files with one MERGE statement. The format of the simple MERGE verb is as follows.
  • 74. The input files to be merged through the MERGE statement are specified in the USING phrase. These files must be sequential files and must be sorted on the merge keys. The rules of the SORT statement in respect of the ASCENDING/DECENDING KEY phrase are also applicable in this case. ALL THE FILES IN THE MERGE STATEMENT MUST HAVE RECORDS OF SAME SIZE AND THE POSITION OF THE MERGE KEY WITHIN THE RECORD DESCRIPTION OF EACH OF THE FILES MUST BE SAME
  • 75. TWO FILES FOR WHICH A RECORD HAVING 2 FIELDS NAMELY ACCOUNT NUMBER AND NAME ARE ALREADY AVAILABLE. MERGE THESE TWO FILES AND CREATE A NEW FILE BASED ON THE ASCENDING ORDER OF ACCOUNT NUMBER. IDENTIFICATION DIVISION. PROGRAM-ID. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION.
  • 76. FILE-CONTROL. SELECT O1-FILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. SELECT O2-FILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. . SELECT M-FILE ASSIGN TO DISK ORGANIZATION IS LINE SEQUENTIAL. SELECT W-FILE ASSIGN TO DISK.
  • 77. DATA DIVISION. FILE SECTION. FD O1-FILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "O1.DAT". 01 O1-REC. 02 O1-ACC-NO PIC 9(2). 02 O1-NAME PIC X(4). FD O2-FILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "O2.DAT". 01 O2-REC. 02 O2-ACC-NO PIC 9(2). 02 O2-NAME PIC X(4).
  • 78. FD M-FILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "M.DAT". 01 M-REC. 02 M-ACC-NO PIC 9(2). 02 M-NAME PIC X(4). SD W-FILE. 01 W-REC. 02 W-ACC-NO PIC 9(2). 02 W-NAME PIC X(4).
  • 79. PROCEDURE DIVISION. P-1. MERGE W-FILE ON ASCENDING KEY W-ACC-NO USING O1-FILE O2-FILE GIVING M-FILE. STOP RUN.
  • 80. DIRECT ACCESS file • Files which are stored on a direct access storage medium such as a magnetic disk, are often called direct access files. • COBOL supports three different organization for disk files • Sequential • relative • and index sequential.
  • 81. • A relative file is a magnetic-disk file organized in such a way that each record is identified by a relative record number. • The relative record number specifies the position of the record from the beginning of the file. • Thus the relative record number 1identifies the first record, the relative record number 2 identifies the second record and so on. • A relative file can be access either sequentially or randomly. RELATIVES file
  • 82. • When the file is accessed sequentially the records are accessed in the increasing order of their relative record numbers. • When a file is accessed randomly, the programmer must specify the relative record number.
  • 83. •In relative organization, the reading as well as the writing can be done randomly. •Thus when a file is created by writing the record randomly, some of the record position may remain empty. •While these positions can be filled in subsequently, the programmer should avoid specifying these empty positions while reading such as relative file randomly. •If a relative file is read in a sequential manner, such empty position within it, if any, are ignored.
  • 84. The handling of relative files requires some special codes in the FILE-CONTROL paragraph as well as in the PROCEDURE DIVISION. FILE-CONTROL paragraph for relative files: The general format for the SELECT clause for a relative file is as follows.
  • 85. ACCESS mode  Sequential Access mode  Random ACCESS MODE IS DYNAMIC  file is accessed sequentially or/and randomly in the Procedure Division The phrase RELATIVE KEY must be specified when access mode is RANDOM or DYNAMIC Dataname-1  called relative key data item  relative record number Programmer must place an appropriate value in the relative key data item  to access randomly Dataname-1  unsigned integer  must not be part of the record description for the said relative file
  • 86. Whether the file should be used sequentially or randomly, should specified through the word SEQUENTIAL or RANDOM in the access mode clause the clause ACCESS MODE IS DYNAMIC it indicates that the file is accessed sequentially and / or randomly in the PROCEDURE DIVISION.
  • 87. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT REL-FILE ASSIGN TO DISK ORGANIZATION IS RELATIVE ACCESS MODE IS DYNAMIC RELATIVE KEY IS RK-NO. FILE SECTION FD REL-FILE LABEL RECORDS ARE STANDARD VALUE OF FILE-ID IS "IN.TXT". 01 REL-REC. 02 REGNO PIC 9(5). 02 NAME PIC X(20). 02 ADDRESS PIC X(20). WORKING-STORAGE SECTION. 77 RK-NO PIC 999.
  • 88. The statements OPEN,CLOSE, READ,WRITE and REWRITE which are available for sequential files are available for the relative files. In addition, two other words, namely, DELETE and START are also available. PROCEDURE DIVISION for relative files
  • 89. READ STATEMENTS: •As usual, a READ statements reads a record of the file. •The file must be open in either the input or I-O mode. There are 3 different general format for the read statements
  • 90. This format is the normal form of the READ statements. •Applicable to sequential file access
  • 91. •Format 2 is used when the access mode is either random or dynamic. •Record to be read is identified from the value in the relative data item MOVE 50 TO REL-KEY. READ EMP-FILE RECORD INVALID KEY PERFORM NOT-FOUND-PARA
  • 92. •Format 3 can be used when the Access mode is dynamic and the records are to be read sequentially. •The next record is identified according to the following rules: (i) When the READ NEXT statements is the first statement to be executed after the open statement on the file, the next record is the first record of the file. (ii) the execution of the READ NEXT statement follows the execution of the start statement  next record is the record logically positioned by the START statement
  • 93. READ REL-FILE next record AT END MOVE -1 TO LAST. IF LAST NOT = -1 DISPLAY REL-REC.
  • 94. WRITE Statement The WRITE statement for a relative file has the following format. The file must be open either in the OUTPUT or I-O mode. •File access is RANDOM  the statement releases the record to that relative record position  indicated by the REL-KEY •In sequential access records are released to the file in the sequential record position
  • 95. The imperative statement of the INVALID KEY phrase is execution in the following case: (i) when an attempt is made to write beyond the externally-defined boundaries of the file. (ii) When an attempt is made to write in the record position which already contains a valid record
  • 96. DISPLAY "ENTER THE DETAILS". ACCEPT REGNO. ACCEPT NAME. ACCEPT ADDRESS. COMPUTE RK-NO = REGNO. DISPLAY "ACCEPT THE VALUE OF RELKEY". ACCEPT RK-NO. WRITE REL-REC.
  • 97. REWRITE STATEMENT: The REWRITE statement has the following format for a relative file, REWRITE record-name [ FROM identifier ] [ ; INVALID KEY imperative –statement ] • The REWRITE statement is used to replace an exiting record by the contents of the record specified in the record name. • The file must be opened in the I-O mode.
  • 98. Access mode  SEQUENTIAL •prior to REWRITE a READ statement on the file should be successfully executed •No need to specify INVALID KEY option here The imperative statement after the INVALID KEY is executed when an attempt is made to replace a record position which is empty Access mode  RANDOM or DYNAMIC •the record to be replaced is identified by the contents of relative key data
  • 99. DELETE STATEMENT: The format of the DELETE statement is as follows: DELETE file-name RECORD [ ; INVALID KEY imperative-statement ] •The file must be opened in I-O mode • ACCESS MODE IS SEQUENTIAL •the execution of the DELETE statement must be preceded by the execution of a READ statement on the file and the INVALID KEY phrase should not be specified. INVALID KEY  when an attempt is made to delete the record of an empty record position
  • 100. START STATEMENT: The format of the START statement is as follows: START file-name KEY IS = DATANAME1 > NOT < [ ; INVALID KEY imperative-statement ] •The START statement enable the programmer to position the relative file at some specified point •ie subsequent sequential operation on this file can start from this point. Open in INPUT or I-O mode
  • 101. INDEXED SEQUENTIAL FILES Relative files  based on relative key To overcome this problem ie to identify the records based on value in the record field  index sequential file
  • 102. INDEXED SEQUENTIAL FILES •In indexed sequential files (also referred to as indexed files), the records are stored in the key sequence order (ascending order). •In addition, some index tables are also created and maintained with the file. •An indexed file on COBOL can be accessed either sequential or randomly. •While creating an indexed file the records can be written only sequentially and in the ascending order of the key.
  • 103. •When an indexed file is accessed randomly, the sequence in which the records are accessed is controlled by the programmer by specifying the value of a data item called record key. •Indexed files in a COBOL program can be handled through suitable special codes in the FILE-CONTROL paragraph and in the PROCEDURE DIVISION.
  • 104. FILE-CONTROL paragraph for indexed files The general format for the SELECT clause for an files is as follows:
  • 105. The ORGANIZATION clause indicates that the file is an indexed file. The RECORD KEY clause specifies the record key data item on the basis of which the file is sequenced. (prime key) The dataname-1 must be an alphanumeric field within the record description for the file Alternate key  must be defined in the record description
  • 106. •Two or more records having the same value for the prime key are not allowed •Duplicates are allowed for alternative keys •Records of an indexed file can be accessed by specifying the primary key or alternative key
  • 107. READ STATEMENT When access mode is RANDOM or DYNAMIC  the records are to be read in a random manner, READ file-name RECORD [ INTO IDENTIFIER ] [ ; KEY IS data-name ] [ ; INVALID KEY imperative-statement ] •The data name in the KEY IS phrase must be either the prime key or the alternative key item. •If the phrase is not specified, the prime key is assumed. MOVE “1234” TO EMPNO. READ EMP-FILE REOCRD KEY IS EMP-NO INVALID KEY PERFORM NOT-FOUND-PARA
  • 108. ACCESS MODE IS SEQUENTIAL OR DYNAMIC  SAME SYNTAX OF RELATIVE FILE
  • 109. WRITE STATEMENT •The records are written to be logical position as determined from the value of the record key. •OUTPUT MODE  the records must be released in the ascending order of the record key values regardless of the ACCESS mode •Records can be released in any order only when the file is opened in I-O mode and Access mode is RANDOM OR DYNAMIC
  • 110. The INVALID KEY condition arises in the following cases: (i) Attempt to write a record beyond the externally defined boundaries of the file. (ii) file is opened in the OUTPUT mode and the value of the record key is not greater than the value of the record key for the previous record written. (iii) When the value of the record key is equal to the record key of a record key already present in the file.
  • 111. REWRITE STATEMENT •File must be opened in the I-O mode, •If SEQENTIAL access mode the value of the record key of the record being replaced must be equal to that of the record last read from this file. The INVALID KEY condition arises (i) when the record key does not match that of an existing record in the file. (ii) For SEQUENTIAL access, when the value of the record key is not identical to that of the last record read from the file.
  • 112. DELETE STATEMENT •Open  I-O mode •If the access is SEQUENTIAL, the INVALID KEY phrase should not be specified •Before executing DELETE there must be successful READ statement. •For RANDOM or DYNAMIC  record to be deleted is determined by the value of record key •INVALID KEY phrase should be specified
  • 113. START Position the file to the first logical record Access mode  SEQUENTIAL or DYNAMIC File opened  I-O or INPUT