Reading COBOL Layouts, Tutorial: How to read a COBOL layout. Converting IBM EBCDIC,packed,comp-3,signed fields,implied decimal,occurs,redefined pic and more Reading COBOL Layouts: Need to convert COBOL data? That's our business! Introduction: This tutorial on how to read a COBOL layout was written specifically for customers of Disc Interchange Service Company who have had a conversion performed and have received a COBOL layout with the data. It is intended to give you enough information to read most simple layouts. It does not cover all topics or everything you would find in a complex layout, and it is intended to explain COBOL layouts only so you can use your converted data, not so you can write COBOL programs. If you need more detail, please refer to one of the many fine COBOL books available.
Most COBOL data files and most of the conversions DISC performs originate on EBCDIC machines, so our discussion assumes an EBCDIC platform. We will discuss some EBCDIC to ASCII conversion issues. This tutorial teaches mostly by example, and progresses from basic rules to simple layouts to more complex layouts. Later examples build on previous examples. To read the article from the beginning, click on Part 1 below. If you only want to review a specific topic, click on the one of interest in the index below.
This tutorial consists of the following 7 sections: Part 1 Introduces you to the elements of a COBOL record layout. Part 2 Presents some simple COBOL layouts and introduces the concept of groups.
Part 3 Discusses what redefined fields are and how they are used. Part 4 Discusses several types of character and binary numeric fields, and the handling of signs and decimal points. Part 5 Introduces tables and the OCCURS and OCCURS DEPENDING ON clauses. Part 6 Discusses redefined records and multiple record types in a file.
Part 7 Conclusion, and notes from the author. Tmw protocol test harness. Additional Information For more articles on data conversion, see our. Our COBOL Conversion Services Disc Interchange Service Company's primary business is converting mainframe COBOL files. From the simplest mailing list to the most complex financial data, we have the tools to properly convert and Q.C.
Your files efficiently and accurately. With over 32 years of experience with thousands of files, we have the knowledge to catch problems with the data before they cause you grief. Daily -to- Monthly Repeat Conversions If you need to convert data on a daily, weekly, or monthly basis, we can write a custom program to convert and Q.C your data to your specifications. Our experience in automating the conversion process results in significantly lower cost, and excellent quality-control. With 32 years experience, we are the experts at transferring mainframe data to PCs. Disc Interchange Service Company, Inc.
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File handling verbs are used to perform various operations on files. Following are the file handling verbs −. Open.
Read. Write. Rewrite. Delete.
Start. Close Open Verb Open is the first file operation that must be performed.
If Open is successful, then only further operations are possible on a file. Only after opening a file, the variables in the file structure are available for processing. FILE STATUS variable is updated after each file operation. Syntax OPEN 'mode' file-name. Here, file-name is string literal, which you will use to name your file. A file can be opened in the following modes − Sr.No.
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Mode & Description 1 Input Input mode is used for existing files. In this mode, we can only read the file, no other operations are allowed on the file. 2 Output Output mode is used to insert records in files. If a sequential file is used and the file is holding some records, then the existing records will be deleted first and then new records will be inserted in the file. It will not happen so in case of an indexed file or a relative file. 3 Extend Extend mode is used to append records in a sequential file. In this mode, records are inserted at the end.
How To Read Cobol Programs
If file access mode is Random or Dynamic, then extend mode cannot be used. 4 I-O Input-Output mode is used to read and rewrite the records of a file. Read Verb Read verb is used to read the file records.
The function of read is to fetch records from a file. At each read verb, only one record can be read into the file structure. To perform a read operation, open the file in INPUT or I-O mode. At each read statement, the file pointer is incremented and hence the successive records are read. Syntax Following is the syntax to read the records when the file access mode is sequential − READ file-name NEXT RECORD INTO ws-file-structure AT END DISPLAY 'End of File' NOT AT END DISPLAY 'Record Details:' ws-file-structure END-READ. Following are the parameters used −.
NEXT RECORD is optional and is specified when an indexed sequential file is being read sequentially. INTO clause is optional. Ws-file-structure is defined in the WorkingStorage Section to get the values from the READ statement. AT END condition becomes True when the end of file is reached.
Example − The following example reads an existing file using line sequential organization. This program can be compiled and executed using Live Demo option where it will display all the records present in the file.
IDENTIFICATION DIVISION. ENVIRONMENT DIVISION. INPUT-OUTPUT SECTION.
SELECT STUDENT ASSIGN TO 'input.txt' ORGANIZATION IS LINE SEQUENTIAL. DATA DIVISION. FILE SECTION. 01 STUDENT-FILE. 05 STUDENT-ID PIC 9(5). 05 NAME PIC A(25).
WORKING-STORAGE SECTION. 01 WS-STUDENT. 05 WS-STUDENT-ID PIC 9(5). 05 WS-NAME PIC A(25). 01 WS-EOF PIC A(1). PROCEDURE DIVISION. OPEN INPUT STUDENT.
PERFORM UNTIL WS-EOF='Y' READ STUDENT INTO WS-STUDENT AT END MOVE 'Y' TO WS-EOF NOT AT END DISPLAY WS-STUDENT END-READ END-PERFORM. CLOSE STUDENT.
Suppose the input file data available in the input.txt file contains the following − 20003 Mohtashim M. 20004 Nishant Malik 20005 Amitabh Bachhan When you compile and execute the above program, it produces the following result − 20003 Mohtashim M. 20004 Nishant Malik 20005 Amitabh Bachhan Syntax Following is the syntax to read a record when the file access mode is random − READ file-name RECORD INTO ws-file-structure KEY IS rec-key INVALID KEY DISPLAY 'Invalid Key' NOT INVALID KEY DISPLAY 'Record Details: ' ws-file-structure END-READ. Example − The following example reads an existing file using indexed organization. This program can be compiled and executed using JCL on Mainframes where it will display all the records present in the file.
On Mainframes server, we do not use text files; instead we use PS files. Let's assume that the file present on Mainframes have same content as input.txt file in the above example. IDENTIFICATION DIVISION. ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION. SELECT STUDENT ASSIGN TO IN1 ORGANIZATION IS INDEXED ACCESS IS RANDOM RECORD KEY IS STUDENT-ID FILE STATUS IS FS. DATA DIVISION.
FILE SECTION. 01 STUDENT-FILE. 05 STUDENT-ID PIC 9(5). 05 NAME PIC A(25). WORKING-STORAGE SECTION. 01 WS-STUDENT.
05 WS-STUDENT-ID PIC 9(5). 05 WS-NAME PIC A(25). PROCEDURE DIVISION. OPEN INPUT STUDENT. MOVE 20005 TO STUDENT-ID. READ STUDENT RECORD INTO WS-STUDENT-FILE KEY IS STUDENT-ID INVALID KEY DISPLAY 'Invalid Key' NOT INVALID KEY DISPLAY WS-STUDENT-FILE END-READ.
CLOSE STUDENT. JCL to execute the above COBOL program − //SAMPLE JOB(TESTJCL,XXXXXX),CLASS = A,MSGCLASS = C //STEP1 EXEC PGM = HELLO //IN1 DD DSN = STUDENT-FILE-NAME,DISP=SHR When you compile and execute the above program, it produces the following result − 20005 Amitabh Bachhan Write Verb Write verb is used to insert records in a file. Once the record is written, it is no longer available in the record buffer. Before inserting records into the file, move the values into the record buffer and then perform write verb. Write statement can be used with FROM option to directly write records from the working storage variables. From is an optional clause. If the access mode is sequential, then to write a record, the file must open in Output mode or Extend mode.
If the access mode is random or dynamic, then to write a record, the file must open in Output mode or I-O mode. Syntax Following is the syntax to read a record when the file organization is sequential − WRITE record-buffer FROM ws-file-structure END-WRITE. Following is the syntax to read a record when the file organization is indexed or relative − WRITE record-buffer FROM ws-file-structure INVALID KEY DISPLAY 'Invalid Key' NOT INVALID KEY DISPLAY 'Record Inserted' END-WRITE. Example − The following example shows how to insert a new record in a new file when the organization is sequential. IDENTIFICATION DIVISION. ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION. SELECT STUDENT ASSIGN TO OUT1 ORGANIZATION IS SEQUENTIAL ACCESS IS SEQUENTIAL FILE STATUS IS FS. DATA DIVISION. FILE SECTION. FD STUDENT 01 STUDENT-FILE.
05 STUDENT-ID PIC 9(5). 05 NAME PIC A(25). 05 CLASS PIC X(3). WORKING-STORAGE SECTION. 01 WS-STUDENT. 05 WS-STUDENT-ID PIC 9(5).
05 WS-NAME PIC A(25). 05 WS-CLASS PIC X(3). PROCEDURE DIVISION. OPEN EXTEND STUDENT. MOVE 1000 TO STUDENT-ID. MOVE 'Tim' TO NAME.
MOVE '10' TO CLASS. WRITE STUDENT-FILE END-WRITE. CLOSE STUDENT. JCL to execute the above COBOL program − //SAMPLE JOB(TESTJCL,XXXXXX),CLASS = A,MSGCLASS = C //STEP1 EXEC PGM = HELLO //OUT1 DD DSN = OUTPUT-FILE-NAME,DISP = (NEW,CATALOG,DELETE) When you compile and execute the above program, it will add a new record to the output file. 1000 Tim 10 Rewrite Verb Rewrite verb is used to update the records. File should be opened in I-O mode for rewrite operations. It can be used only after a successful Read operation.
Rewrite verb overwrites the last record read. Syntax Following is the syntax to read a record when the file organization is sequential − REWRITE record-buffer FROM ws-file-structure END-REWRITE. Following is the syntax to read a record when the file organization is indexed or relative − REWRITE record-buffer FROM ws-file-structure INVALID KEY DISPLAY 'Invalid Key' NOT INVALID KEY DISPLAY 'Record Updated' END-REWRITE. Example − The following example shows how to update an existing record which we have inserted in the previous Write step − IDENTIFICATION DIVISION. ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION. SELECT STUDENT ASSIGN TO IN1 ORGANIZATION IS INDEXED ACCESS IS RANDOM RECORD KEY IS STUDENT-ID FILE STATUS IS FS. DATA DIVISION. FILE SECTION. FD STUDENT 01 STUDENT-FILE. 05 STUDENT-ID PIC 9(4). 05 NAME PIC A(12).
05 CLASS PIC X(3). WORKING-STORAGE SECTION. 01 WS-STUDENT. 05 WS-STUDENT-ID PIC 9(5). 05 WS-NAME PIC A(25).
05 WS-CLASS PIC X(3). PROCEDURE DIVISION. OPEN I-O STUDENT. MOVE '1000' TO STUDENT-ID. READ STUDENT KEY IS STUDENT-ID INVALID KEY DISPLAY ‘KEY IS NOT EXISTING’ END-READ. MOVE 'Tim Dumais' TO NAME.
REWRITE STUDENT-FILE END-REWRITE. CLOSE STUDENT. JCL to execute the above COBOL program − //SAMPLE JOB(TESTJCL,XXXXXX),CLASS = A,MSGCLASS = C //STEP1 EXEC PGM = HELLO //IN1 DD DSN = OUTPUT-FILE-NAME,DISP = SHR When you compile and execute the above program, it will update the record − 1000 Tim Dumais 10 Delete Verb Delete verb can be performed only on indexed and relative files. The file must be opened in I-O mode.
In sequential file organization, records cannot be deleted. The record last read by the Read statement is deleted in case of sequential access mode. In random access mode, specify the record key and then perform the Delete operation. Syntax Following is the syntax to delete a record − DELETE file-name RECORD INVALID KEY DISPLAY 'Invalid Key' NOT INVALID KEY DISPLAY 'Record Deleted' END-DELETE. Example − to delete an existing record − IDENTIFICATION DIVISION. ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION. SELECT STUDENT ASSIGN TO OUT1 ORGANIZATION IS INDEXED ACCESS IS RANDOM RECORD KEY IS STUDENT-ID FILE STATUS IS FS. DATA DIVISION. FILE SECTION. FD STUDENT 01 STUDENT-FILE. 05 STUDENT-ID PIC 9(4). 05 NAME PIC A(12).
05 CLASS PIC X(3). WORKING-STORAGE SECTION. 01 WS-STUDENT. 05 WS-STUDENT-ID PIC 9(5). 05 WS-NAME PIC A(25). 05 WS-CLASS PIC X(3). PROCEDURE DIVISION.
OPEN I-O STUDENT. MOVE '1000' TO STUDENT-ID. DELETE STUDENT RECORD INVALID KEY DISPLAY 'Invalid Key' NOT INVALID KEY DISPLAY 'Record Deleted' END-DELETE.
CLOSE STUDENT. JCL to execute the above COBOL program − //SAMPLE JOB(TESTJCL,XXXXXX),CLASS = A,MSGCLASS = C //STEP1 EXEC PGM = HELLO //OUT1 DD DSN = OUTPUT-FILE-NAME,DISP = SHR When you compile and execute the above program, it produces the following result − Record Deleted Start Verb Start verb can be performed only on indexed and relative files. It is used to place the file pointer at a specific record. The access mode must be sequential or dynamic. File must be opened in I-O or Input mode.
Syntax Following is the syntax to place the pointer at a specific record − START file-name KEY IS =, , = rec-key INVALID KEY DISPLAY 'Invalid Key' NOT INVALID KEY DISPLAY 'File Pointer Updated' END-START. Close Verb Close verb is used to close a file. After performing Close operation, the variables in the file structure will not be available for processing.
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The link between program and file is lost. Syntax Following is the syntax to close a file − CLOSE file-name.
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