Advanced COBOL slide

Calling a Subprogram• Syntax for CALL CALL “subprog name” [ USING [BY REFERENCE | BY CONTENT] ident1 …] END-CALL • The subprog name usually refers to an 8 byte field that contains th

Advanced COBOL

IBM Enterprise COBOL for z/OS

http://www-306.ibm.com/software/awdtools/cobol/zos/library/

Especially helpful for programmers:

Language Reference Manual

Programming Guide

QSAM File Processing

Queued Sequential Access

Method

QSAM Files

• Unkeyed, Sequentially created and processed

• Records cannot change length or position

• QSAM files on direct access storage can be modified with REWRITE

Environment Division - File Control

Environment Division

File-CONTROL

• Optional – used for files opened in I-O, INPUT,

or EXTEND File doesn’t have to be present

when the program is executed.

• File-name1 – identifies an FD entry (internal file name)

• Assignment-name – identifies the external file If name component of the SELECT clause is found

in the JCL it is treated as a DD name If not

found in the JCL, then “name” is treated an an

environment variable

QSAM File Name

name

label-

• Label – documents for the programmer the device and device class to

which the file is assigned No effect on execution Must end with a

dash

• S – Optional Indicates sequential organization

Environment Variables

Exercise A (Dynamic Files)

• Statically allocate and read

BCST.SICCC01.TESTPDS(DYNAMDAT)

• This file contains member names of other members in BCST.SICCC01.TESTPDS

• Dynamically Read each member that is listed and

display the records in each member

• After you can display all the records, try writing out the records to a dynamically allocated file

• Use BCST.SICCC01.PDSLIB(DYNAM2) to help you read a file dynamically

• Use BCSC.SICCC01.PDSLIB(DYNAM1) to help you write a file dynamically

Reserve Clause (optional)

RESERVE integer

AREA

AREAS

RESERVE Clause

• Specifies the number of I/O buffers

allocated the file at run-time

• If omitted, the number of buffers is taken from the DD statement If none are

specified, the system default is taken

QSAM Buffering

• QSAM buffers can be allocated above the 16 MB line if all of the following are true:

- Enterprise COBOL

- z/OS Language Environment

- the programs are compiled with RENT and DATA(31)

or

compiled with NORENT and | RMODE(ANY)

- the program is executing in AMODE 31

- the program is executing on MVS

- the ALL31(ON) run-time option is used (for

EXTERNAL files)

ORGANIZATION Clause (optional)

• ORGANIZATION IS SEQUENTIAL

• Other non-QSAM options: INDEXED,

RELATIVE, LINE SEQUENTIAL

• Records are read and written in a serial manner

PADDING Clause

PADDING data name CHARACTER IS literal

Specifies a character for block padding on sequential files

Data name – a one character field

Literal – a one character alphanumeric literal or national symbol

ACCESS MODE Clause

ACCESS SEQUENTIAL MODE IS

Default mode is SEQUENTIAL

Options for other types of files include RANDOM and DYNAMIC

FILE STATUS Clause

STATUS dname1

FILE IS dname2

- The operating system moves a value to dname1 and possibly dname2 after each I/O operation.

-dname1 - a two character alphanumeric or national field

-dname2 – used for VSAM

APPLY WRITE-ONLY ON MYFILE.

(Used for sequential variable blocked files.)

Defining QSAM Files and Records

FILE-CONTROL

SELECT CUSTOMER-MASTER ASSIGN TO CUSTMASTORGANIZATION IS SEQUENTIALACCESS MODE IS SEQUENTIAL FILE STATUS IS RC

DATA DIVISION FILE SECTION - Sequential

DATA DIVISION

FILE SECTION - FD

• The EXTERNAL clause specifies that a file connector is external, permitting file sharing between two programs in the

same run unit

• GLOBAL clause specifies the

file-connector name is available to the declaring program and all programs contained directly or indirectly

• Used for nested programs

BLOCK CONTAINS

• BLOCK CONTAINS 0 RECORDS

• If this clause is omitted, records are unblocked

by default!

• Allows the blocksize to be specified in the JCL or

by the operating system

• Code this Statement! (TSYS Standard)

• RECORD CONTAINS 80 CHARACTERS

• RECORD CONTAINS 50 TO 80 CHARACTERS

• RECORD IS VARYING IN SIZE

FROM 40 TO 60 CHARACTERS

DEPENDING ON REC-COUNT.

RECORDING MODE

• Specifies the format of physical records in

a QSAM file (ignored for VSAM)

• F – fixed size, V – variable size, U –

unblocked, fixed or variable, S – spanned, large records that span a block

• RECORDING MODE IS F

• RECORDING MODE IS V

• RECORDING MODE IS U

• RECORDING MODE IS S

DATA RECORD Clause

• DATA RECORD clause identifies the data areas associated with the file

• Syntax checked but is only documentation

DATA RECORD IS INPUT-AREA

DATA RECORDS ARE INPUT-AREA1

INPUT-AREA2

FD Example

FD IN-FILE IS GLOBAL

RECORDING MODE F

BLOCK CONTAINS 0 RECORDS

LABEL RECORDS ARE STANDARD

RECORD CONTAINS 80 CHARACTERS DATA RECORD IS IN-AREA.

01 IN-AREA.

05 …

LABEL RECORDS

• Label records are records written at the

beginning and end of DASD and Tape

files that provide information about file

• Enterprise COBOL only supports standard labels

LABEL RECORDS ARE STANDARD

LABEL RECORDS ARE OMITTED

Subprograms

Calling a Subprogram

• Syntax for CALL

CALL “subprog name”

[ USING [BY REFERENCE | BY CONTENT]

ident1 …]

END-CALL

• The subprog name usually refers to an 8 byte field that contains the program name to be called

• Static call is made when subprogram name is

hard-coded and compiler option = NODYNAM

• Subprogram can be written in any supported

language

• The variable-name usually refers to an 8 byte

field that contains the program name to be called

• Names can be longer with Enterprise COBOL

• The variable-name can be modified as the

program is running to call different programs

Calling a Subprogram

• Linking to the called program is dynamic

• At TSYS, all calls are dynamic ( DYNAM

compiler option)

• BY REFERENCE is the default

• BY REFERENCE provides the subprogram with access to a main program variable The

receiving variable is an alias for the passed

variable

• BY CONTENT provides the subprogram with

access to a copy of a main program variable

Calling a Subprogram

• BY CONTENT ADDRESS OF provides a copy of the address of the passed variable (must be a linkage area name)

• BY CONTENT LENGTH provides a copy

of the length of a variable

Example Parameters

The Called Program

• Specifies the names of the receiving variables with a USING

statement in the PROCEDURE DIVISION statement or in an

PROCEDURE DIVISION USING A COST RESULT.

• The variables in the using statement are 01 group items defined in the LINKAGE SECTION or 77 items

LINKAGE SECTION.

01 A PIC X(8).

O1 COST PIC S9(5) PACKED-DECIMAL.

01 RESULT PIC S9(5) BINARY.

The Called Program

• The called program can return values to the calling program by modifying variables that are passed by reference

PROCEDURE DIVISION USING

COST.

…

MOVE ITEM-COST TO COST

• Call the subprogram

• Print “I am in the subprogram” in the

subprogram

• Print “I am back in the main program” in the main

Exercise #2

• Create a two variables X and Y in the main program (you pick the type and value).

• Print the values of X and Y in the main program

• Pass X BY REFERENCE and Y BY CONTENT to the

subprogram

• Print the variables in the subprogram

• Change the values of each variable in the subprogram

• Print the length of x by passing the length using BY

CONTENT LENGTH (Receiving variable PIC S9(8)

BINARY)

• Print the values of the variables again in the main

program

Canceling a Subprogram

• CANCEL syntax

CANCEL literal

CANCEL identifier

• Canceling a program means the program will be

in its initial state if the program is called again

• Canceling a program closes all files associated with an internal file connector of the canceled

program

• No action is taken when canceling a previously canceled program or one that has not been

dynamically called

Exercise #3

• Have the main program call a subprogram four times

• Create a local numeric variable Z in the

subprogram with initial value 1

• Each time the program is called, print Z

and then add 1 to it

• Repeat the experiment after adding “IS

INITIAL” to the PROGRAM-ID

• Subprograms remain in their last used

state when they terminate with EXIT

PROGRAM or GOBACK

• A program that is coded with INITIAL will always be called with its initial state

Exercise #4

• Repeat Exercise #3, canceling each program after each subprogram call

Return Codes

• Use the RETURN-CODE special register

to test and transmit return codes through register 15

• After calling a subprogram, test CODE to see if the subprogram completed normally

• At the end of a suprogram, set CODE to indicate the results of the call

RETURN-Exercise #5

Write a main program that passes a numeric

parameter, say X, to a subprogram If the

parameter is negative have the subprogram set

a return code of 4 If the parameter is

non-negative, the subprogram should set the return code to 0 Have the main program test the

return code after the subprogram has

completed The main program should print a message indicating the type of number the

subprogram received Try running the main

program passing negative and non-negative

values for X.

Reading Records

• READ MYFILE INTO MY-RECORD

– Move mode IO – Data flows from an I/O buffer into working storage.

• READ MYFILE

– Locate mode I/O – Data remains in an I/O

buffer Efficient processing technique

– TSYS standard

External Files

• Make the file status field external so there

is only one shared field for all programs Each program declares:

01 MYSTATUS PIC 99 EXTERNAL

• Be sure to work in locate-mode

Exercise #6

• Write a main program that opens a sequential file and calls a subprogram each time it needs a record Write a subprogram that reads a single record and returns to the main program Have the main program print all the records in the

sequential file and then close the file.

• Share the same file between the two programs

by making the file external with a shared file

status field.

PROCEDURE DIVISION…

RETURNING

• An alternate form of passing information back to a calling program is provided:

PROCEDURE DIVISION RETURNING dataname

• To call a “Function” the invocation is:

CALL program-name RETURNING dataname

• Avoid this alternative in favor of Pass By

Reference.

Nested Programs

• Avoided in production programs at TSYS

• Convenient for developing (one file, one compilation)

• Nested programs can be separated easily into regular programs after debugging

• Can be used instead of PERFORM

• CALL to a nested program is as efficient

as a PERFORM

• Each program ends with END PROGRAM

Nested Program Structure

X1

Exercise #7

• Convert one of your main programs and

subprograms to a nested program version

• Canceling only makes sense for

dynamically called programs

• Cause an abend in your subprogram

Look at the storage dump and error

information Is it any harder to debug than

a regular program?

COBOL is Recursive Now

• A COBOL program can call itself

• To make a program recursive, add “IS RECURSIVE” to the PROGRAM-ID

statement

PROGRAM-ID SUBPROG IS RECURSIVE.

• Nested programs cannot be recursive

Passing a Parm with JCL

• A parm can be coded on the EXEC statement in order to pass a parameter to the program that is being executed: // EXEC PGM=PROGNAME,PARM=‘HI there!'

• The COBOL program will receive the parm through the LINKAGE SECTION

• Code a LINKAGE SECTION description similar to this:

01 PARM-BUFF.

05 PARM-LEN PIC S9(4) BINARY.

05 PARM-DATA PIC X(256).

• Code a using statement on the PROCEDURE DIVISION

PROCEDURE DIVISION USING PARM-BUFF.

Passing a Parm with JCL

• The parm field is variable in length

• Use the length field and reference

modification to move variable length data MOVE PARM-DATA(1:PARM-LEN)TO PARMO

Omitted Parameters

• You can leave out some arguments when coding

a CALL statement by coding OMITTED in place

of the passed variable

CALL “THATPROG” USING P1,OMITTED,P3

• Test for the OMITTED parameter by checking to see if the address of the received parm is NULL PROCEDURE DIVISION USING X Y Z.

…

IF ADDRESS OF Y = NULL

DISPLAY “PARM Y WAS NOT PASSED”

END-IF

Tables

Creating A Single Dimension Table

• Build a storage area with list of data

values defined with multiple picture

clauses

• Redefine the storage area as a single

dimension table by defining a typical table entry as an “occuring” item

Creating A Single Dimension Table

01 DAY-TABLE-VALUES.

05 PIC X(9) VALUE 'SUNDAY '.

05 PIC X(9) VALUE 'MONDAY '.

05 PIC X(9) VALUE 'TUESDAY '.

05 PIC X(9) VALUE 'WEDNESDAY'.

05 PIC X(9) VALUE 'THURSDAY '.

05 PIC X(9) VALUE 'FRIDAY '.

05 PIC X(9) VALUE 'SATURDAY '

01 DAY-TABLE REDEFINES DAY-TABLE-VALUES.

05 WEEKDAY PIC X(9) OCCURS 7 TIMES.

“Fat” Single-Dimension Tables

Exercise #9

• Implement a single dimension table of

days Print the table from beginning to

end

• Turn the table into a “fat” table by adding a column with the number of letters in each day name

• Print each day name and the number of

letters it contains

HRS(1,1) HRS(2,1) HRS(3,1)

HRS(1,2) HRS(1,3) HRS(2,2) HRS(2,3)

HRS(3,3) HRS(3,2)

EMPLOYEE(3)

Exercise #10

• Create a table of integers with 4 rows and

5 columns

• Print the table row by row

• Print the table column by column

• Compute and print the sum of each row

• Compute and print the sum of each

column

• Compute and print the sum of all entries in the table

Creating Tables with Indexes

Subscripts vs Indexes

• Subscripts

– Represent an occurrence number

– User defined as a numeric field – best to choose USAGE IS BINARY

– Printable (since they are numeric)

– Can use relative subscripts J+1 or J-3 – Manipulated with PERFORM loops,

assignments, and arithmetic commands

Subscripts vs Indexes

• Indexes

– Represent a displacement value from the start

of a table.

– More efficient than subscripts

– Created automatically when a table is defined with indexes

– Not really designed to be printed

– Manipulated with PERFORM loops, and SET statements

Exercise #11

• Convert Exercise #10 so that you are using indexes instead of subscripts

Sequential Search

• COBOL provides a SEARCH command that provides a sequential search for

tables that have indexes

• Table entries do not have to be sorted

• AT END clause provides code in the

situation that the search is unsuccessful

• Searching starts with the current index value

SEARCH

Exercise #12

• Create a fat single dimension table with

the data in the file DATA1 Read the file and store the second (Item #) and third

fields (Item name) in the table

• Assume a fixed size table of 40 items

• Sequentially search the table for item #s in the range 400 to 450 Print out the results

of the search

Binary Searching

• Entire table is searched No need to initialize an index

• Table must have an ASCENDING or

DESCENDING KEY IS clause Table must be sorted.

• Only one WHEN clause allowed The WHEN

clause is comprised of one or more “equal” tests joined by AND operators

• AT END clause is invoked if the WHEN clause is never satisfied