98509729 Cobol File Handling

8/13/2019 98509729 Cobol File Handling

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File Handling in

COBOL


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Topics covered in the Session

(1) Introduction to File handling.

(2) File ORGANIATION and A!!"SS #ethods.

($) File handling ver%s.


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&'212&'212&*$' A+&*$' A+ In,os-s Technologies i#itedIn,os-s Technologies i#ited

COBOL is generally used inCOBOL is generally used insituations where the volume ofsituations where the volume of

data to be processed is large.data to be processed is large.

These systems are sometimesThese systems are sometimes

referred to as data intensivereferred to as data intensive

systems.systems.


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Introduction to File processing

Field Field type and Field sie.

!ecord !ecord"#ie$ Fi%ed length records and&ariable length records.

File 'aster files$ Transaction files$ Fileorganiation and File access method.

/asic Ter#inologies


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Fields.Fields. 0e use the ter# FI" to descri%e an ite# o,0e use the ter# FI" to descri%e an ite# o,

in,or#ation e are recording a%out an o%3ectin,or#ation e are recording a%out an o%3ect

(e.g. StudentNa#e4 ateO,/irth4 !ourse!ode).(e.g. StudentNa#e4 ateO,/irth4 !ourse!ode).

0e use the ter# R"!OR to descri%e the collection o,0e use the ter# R"!OR to descri%e the collection o,,ields hich record in,or#ation a%out an o%3ect,ields hich record in,or#ation a%out an o%3ect

(e.g. a StudentRecord is a collection o, ,ields(e.g. a StudentRecord is a collection o, ,ields

recording in,or#ation a%out a student).recording in,or#ation a%out a student).

0e use the ter# FI" to descri%e a collection o, one or0e use the ter# FI" to descri%e a collection o, one or#ore occurrences (instances) o, a record t-pe#ore occurrences (instances) o, a record t-pe(te#plate).(te#plate).

It is i#portant to distinguish %eteen the recordIt is i#portant to distinguish %eteen the recordoccurrence (i.e. the values o, a record) and the recordoccurrence (i.e. the values o, a record) and the recordt-pe (i.e. the structure o, the record).t-pe (i.e. the structure o, the record)."ver- record in a ,ile has a di,,erent value %ut the sa#e"ver- record in a ,ile has a di,,erent value %ut the sa#e

structure.structure.


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Fields.Fields.

StudId StudName DateOfBirthStudId StudName DateOfBirth

9723456 COUGHLAN 1919619724567 !"AN 31121976953411# CO$$%" 2361964942345# O&B!I%N 31119799312#76 S'I(H 12121976

StudId StudName DateOfBirthStudId StudName DateOfBirth

9723456 COUGHLAN 1919619724567 !"AN 31121976953411# CO$$%" 2361964942345# O&B!I%N 31119799312#76 S'I(H 12121976

S(UD%N(SS(UD%N(S

DA(A DI)ISION*$IL% S%C(ION*

$D Stude+t$i,e*1 Stude+tDetai,-* 2 StudId .IC 9/70* 2 StudName .IC /#0* 2 DateOfBirth .IC /#0*

DA(A DI)ISION*$IL% S%C(ION*

$D Stude+t$i,e*1 Stude+tDetai,-* 2 StudId .IC 9/70* 2 StudName .IC /#0* 2 DateOfBirth .IC /#0*

occurrencesoccurrences

Record TypeRecord Type(Template)(Template)

(Structure)(Structure)


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"5a#ple

!()*O *+'( +)(

6A1&1 78OT9I 1:

6A1&2 ANIR;9 2&6A1&$ SRI9AR 1

Field


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BuffersBuffers

To process a file records are read from theTo process a file records are read from the

file into the computers memory one recordfile into the computers memory one recordat a time.at a time.

The computer uses the programmersThe computer uses the programmers

description of the record /i.e. the recorddescription of the record /i.e. the recordtemplate0 to set aside sufficient memory totemplate0 to set aside sufficient memory to

store one instance of the record.store one instance of the record.

'emory allocated for storing a record is'emory allocated for storing a record is

usually called a record bufferusually called a record buffer

The record buffer is the only connectionThe record buffer is the only connection

between the program and the records in thebetween the program and the records in the

file.file.


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BuffersBuffers

IDENTIFICATION DIVISION.

etc.

ENVIRONMENT DIVISION.

etc.

DATA DIVISION.FIE SECTION.

!ro"ram!ro"ram

Record#u$$erRecord#u$$er

Declarat%onDeclarat%onST&DENTS

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Record Instance


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escription o, a Record %u,,er ,or a ,ile containing

Single record t-pe

-+T+ -1&1#1O*.

F1L( #(CT1O*.

F- #T,-F1L(.

34 #T,-"!(C.

35 !()*O 61C 7/50.

35 *+'( 61C +/450.35 +)( 61C 8/90.

Record /u,,er and its i#plications


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COBOLCOBOL

The record type:template:buffer ofThe record type:template:buffer of everyeveryfile used in afile used in aprogramprogram mustmustbe described in the F1L( #(CT1O* bybe described in the F1L( #(CT1O* by

means of an F- /file description0 entry.means of an F- /file description0 entry.

The F- entry consists of the letters F- and an internal fileThe F- entry consists of the letters F- and an internal file

name.name.

DA(A DI)ISION*$IL% S%C(ION*$D Stude+t$i,e*

1 Stude+tDetai,-* 2 Stude+tId .IC 9/70* 2 Stude+tName* 3 Sur+ame .IC /#0* 3 I+itia,- .IC * 2 DateOfBirth* 3 "OBirth .IC 9/20* 3 'OBirth .IC 9/20*

3 DOBirth .IC 9/20* 2 Cur-eCde .IC /40* 2 Gra+t .IC 9/40* 2 Ge+der .IC *

DA(A DI)ISION*$IL% S%C(ION*$D Stude+t$i,e*1 Stude+tDetai,-* 2 Stude+tId .IC 9/70* 2 Stude+tName* 3 Sur+ame .IC /#0* 3 I+itia,- .IC * 2 DateOfBirth* 3 "OBirth .IC 9/20* 3 'OBirth .IC 9/20*

3 DOBirth .IC 9/20* 2 Cur-eCde .IC /40* 2 Gra+t .IC 9/40* 2 Ge+der .IC *


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;Buffers;Buffers

1f your program processes more than one file you1f your program processes more than one file you

will have to describe a record buffer for each file.will have to describe a record buffer for each file.

To process all the records in an 1*6,T file eachTo process all the records in an 1*6,T file each

record instance must be copied /read0 from the filerecord instance must be copied /read0 from the file

into the record buffer when re


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escription o, a Record %u,,er ,or a ,ile containing+ultiple record t-pes

-+T+ -1&1#1O*.

F1L( #(CT1O*.

F- T!+*#"F1L(.

34 1*#"!(C. 35 T"CO-( 61C 7.

35 !()*O 61C 7/50.

35 *+'( 61C +/450.

35 +)( 61C 8/90.

34 -(L"!(C.

35 T"CO-( 61C 7.

35 !()*O 61C 7/50.

34 ,6-"!(C.

35 T"CO-( 61C 7.

35 !()*O 61C 7/50.

35 +)( 61C 8/90.

Record /u,,er and its i#plications

++


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+ccess+ccess Two important characteristics of files areTwo important characteristics of files are

-+T+ O!)+*1=+T1O*-+T+ O!)+*1=+T1O*

'(T>O- OF +CC(##'(T>O- OF +CC(##

-ata organiation refers to the way the records of the file are-ata organiation refers to the way the records of the file are

organied on the bac?ing storage device.organied on the bac?ing storage device.

COBOL recognies three main file organiations@COBOL recognies three main file organiations@

#e


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OrganiationOrganiation

The simplest COBOL file organiation is #e


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Se=uential ,ile organi>ation

#implest and least fle%ible of all types of file

organiations.

Can only be accessed se


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FI"

#(L(CT file"name +##1)* TO implementor"name

A O!)+*1=+T1O* 1# #(,(*T1+L

A +CC(## 'O-( 1# #(,(*T1+L

A F1L( #T+T,# 1# identifier .

ClCl


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ST&DENTS

Clause.Clause.

The internal ,ile na#e used in the F entr- isThe internal ,ile na#e used in the F entr- isconnected to an e5ternal ,ile (on dis? or tape) %-connected to an e5ternal ,ile (on dis? or tape) %-

#eans o, the Select and Assign clause.#eans o, the Select and Assign clause.

%N)I!ON'%N( DI)ISION*IN.U(OU(.U( S%C(ION*$IL%CON(!OL* S%L%C( Stude+t$i,e

ASSIGN (O S(UD%N(S*

DA(A DI)ISION*$IL% S%C(ION*$D Stude+t$i,e*1 Stude+tDetai,-* 2 Stude+tId .IC 9/70*

2 Stude+tName* 3 Sur+ame .IC /#0* 3 I+itia,- .IC * 2 DateOfBirth* 3 "OBirth .IC 9/20* 3 'OBirth .IC 9/20* 3 DOBirth .IC 9/20* 2 Cur-eCde .IC /40*

2 Gra+t .IC 9/40* 2 Ge+der .IC *

%N)I!ON'%N( DI)ISION*IN.U(OU(.U( S%C(ION*$IL%CON(!OL* S%L%C( Stude+t$i,e

ASSIGN (O S(UD%N(S*

DA(A DI)ISION*$IL% S%C(ION*$D Stude+t$i,e*1 Stude+tDetai,-* 2 Stude+tId .IC 9/70* 2 Stude+tName*

3 Sur+ame .IC /#0* 3 I+itia,- .IC * 2 DateOfBirth* 3 "OBirth .IC 9/20* 3 'OBirth .IC 9/20* 3 DOBirth .IC 9/20* 2 Cur-eCde .IC /40* 2 Gra+t .IC 9/40* 2 Ge+der .IC *

-1#2


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F entries ,or Fi5ed length records

F- file"name

A !(CO!- CO*T+1*# integer"4 C>+!+CT(!#

A BLOC2 CO*T+1*# integer"9 D !(CO!-#$

C>+!+CT(!# E

A L+B(L D !(CO!- 1#$ !(CO!-# +!( E

D #T+*-+!-$ O'1TT(- E

A -+T+ D !(CO!- 1#$ !(CO!-# +!( E identifier"4$

identifier"9$ . . .


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F entries ,or @aria%le length records

F- file"name

A !(CO!- CO*T+1*# integer"4 TO integer"9

C>+!+CT(!#

A BLOC2 CO*T+1*# integer" TO integer"GC>+!+CT(!#

A L+B(L D !(CO!- 1#$ !(CO!-# +!( E

D #T+*-+!-$ O'1TT(- E

A -+T+ D !(CO!- 1#$ !(CO!-# +!( E identifier"4$

identifier"9$ . . .


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File handling ver%s

O"N

R"A

0RIT"

R"0RIT"

!OS"

& b& b


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&erbs&erbs O6(*O6(*

Before your program can access the data in an input file orBefore your program can access the data in an input file orplace data in an output file you must ma?e the file available toplace data in an output file you must ma?e the file available tothe program by O6(*ing it.the program by O6(*ing it.

!(+-!(+-The !(+- copies a record occurrence:instance from the fileThe !(+- copies a record occurrence:instance from the fileand places it in the record buffer.and places it in the record buffer.

H!1T(H!1T(The H!1T( copies the record it finds in the record buffer toThe H!1T( copies the record it finds in the record buffer tothe file.the file.

CLO#(CLO#(Iou must ensure that /before terminating0 your programIou must ensure that /before terminating0 your programcloses all the files it has opened. Failure to do so may result incloses all the files it has opened. Failure to do so may result in

data not being written to the file or users being preventeddata not being written to the file or users being preventedfrom accessing the file.from accessing the file.

tt


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synta%synta%

Hhen you open a file you have to indicate to theHhen you open a file you have to indicate to the

system what how you want to use it /e.g. 1*6,T$system what how you want to use it /e.g. 1*6,T$

O,T6,T$ (7T(*-0 so that the system can manageO,T6,T$ (7T(*-0 so that the system can manage

the file correctly.the file correctly.

Opening a file does not transfer any data to theOpening a file does not transfer any data to the

record buffer$ it simply provides access.record buffer$ it simply provides access.

O"N InternalFileNa#e ...

IN;T

O;T;T

"BT"N1


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O"N ver% S-nta5

O"N CIN;T4 O;T;T4 I


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The !(+- verbThe !(+- verb

Once the s-ste# has opened a ,ile and #ade itOnce the s-ste# has opened a ,ile and #ade it

availa%le to the progra# it is the progra##ersavaila%le to the progra# it is the progra##ers

responsi%ilit- to process it correctl-.responsi%ilit- to process it correctl-.

Re#e#%er4 the ,ile record %u,,er is our onl-Re#e#%er4 the ,ile record %u,,er is our onl-

connection ith the ,ile and it is onl- a%le toconnection ith the ,ile and it is onl- a%le to

store a single record at a ti#e.store a single record at a ti#e.

To process all the records in the ,ile e have toTo process all the records in the ,ile e have to

trans,er the#4 one record at a ti#e4 ,ro# the ,iletrans,er the#4 one record at a ti#e4 ,ro# the ,ileto the %u,,er.to the %u,,er.

!O/O provides the R"A ver% ,or this!O/O provides the R"A ver% ,or this

purpose.purpose.

synta%synta%


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synta%synta%

The 1nternalFilename specified must be a file that hasThe 1nternalFilename specified must be a file that has

been O6(*ed for 1*6,T.been O6(*ed for 1*6,T.

The *(7T !(CO!- clause is optional and generallyThe *(7T !(CO!- clause is optional and generally

not used.not used.

,sing 1*TO 1dentifier clause causes the data to be,sing 1*TO 1dentifier clause causes the data to be

read into the record buffer and then copied from thereread into the record buffer and then copied from there

to the specified 1dentifier in one operation.to the specified 1dentifier in one operation.

Hhen this option is used there will be two copiesHhen this option is used there will be two copies

of the data. 1t is the e


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0or?ing o, the R"A state#ent#T,-"!(C

1 & 1 7 8 O T 9 I 2 E/ ;

!()*O *+'( +)(

1 $ A 9 N 2/

(OF

1 2 I 9 A 2/

& R ! A &;

& N T 8 2;

A

#T,-(*T

"RFOR+ ;NTI ST;


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#ynta%#ynta%


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#ynta%.#ynta%.

To 0RIT" data to a ,ile #ove the dataTo 0RIT" data to a ,ile #ove the data

to the record %u,,er (declared in the Fto the record %u,,er (declared in the F

entr-) and then 0RIT"entr-) and then 0RIT"the contents o,the contents o,

record %u,,er to the ,ile.record %u,,er to the ,ile.

0RIT"

A1@AN!ING

AdvanceNu#

+ne#onicNa#e

AG"

RecordNa#e FRO+ Identi,ier

/"FOR"

AFT"R

IN"

IN"S

wor?swor?s


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FF rr aa nn '' CC uu rr tt aa %% nn ** ++ ,, -- MM ++ //

StudentID StudentName Course.

StudentRecord

FF rr aa nn '' CC uu rr tt aa %% nn ** ++ ,, -- MM ++ //

EOF

wor?swor?s

O.%N OU(.U( Stude+t$i,e*'O)% 9334567$ra+ Curtai+ L'51 (O Stude+tDetai,-*

8!I(% Stude+tDetai,-*

'O)% 93#3715(hma- Hea, L'6# (O Stude+tDetai,-*

8!I(% Stude+tDetai,-*CLOS% Stude+t$i,e*

S(O. !UN*

O.%N OU(.U( Stude+t$i,e*

'O)% 9334567$ra+ Curtai+ L'51 (O Stude+tDetai,-*

8!I(% Stude+tDetai,-*

'O)% 93#3715(hma- Hea, L'6# (O Stude+tDetai,-*8!I(% Stude+tDetai,-*

CLOS% Stude+t$i,e*S(O. !UN*

Students


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0or?ing o, the 0RIT" state#ent

#T,-"!(C

1 & 1 7 8 O T 9 I 2 E/ ;

!()*O *+'( +)(

(OF

1 & 1 7 8 O T 9 I 2 E;

+O@" /;1&178OT9I 2EH TO ST;


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0or?ing o, the 0RIT" state#ent

!()*O *+'( +)(

(OF

1 & 2 N I T 9 8 A 2 2/ ;

1 & 2 N I T 9 8 A 2 2/ ;

1 & 1 7 8 O T 9 I 2 E;/

#T,-"!(C

#T,-(*T

+O@" /;1&178OT9I 2EH TO ST;


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R"0RIT" ver%

R"0RIT" is used to update an e5isting record inthe ,ile

S-nta5

!(H!1T( record"name A F!O' identifier"4

*oteJ

The !(H!1T( statement can only be used if the file is

opened in the 1"O mode and its e%ecution must bepreceded by the successful !(+- statement on the file.

The !(H!1T( statement replaces last read record


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!OS" ver%

S-nta5

CLO#( filename4

!eleases the named files from the program.

1f a file is stored on a magnetic tape$ after the

e%ecution

of the CLO#( statement the tape is rewound.

1s optional for COBOL" K5.


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Se=uential ,iles


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+ny+nyuestions uestions


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Than? youThan? you

98509729 Cobol File Handling

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