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DD name access using multiple logical names

 
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chandraBE

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Joined: 02 Feb 2010
Posts: 41
Location: Bangalore

PostPosted: Wed Apr 30, 2014 2:45 pm    Post subject: DD name access using multiple logical names
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JCL DD statement.
Code:
//FILE1  DD DSN=HLQ.FILE1,DISP=SHR


Code:
FILE-CONTROL.

SELECT   FILE1-SEQ                    ASSIGN          TO FILE1
                                      ACCESS MODE     IS SEQUENTIAL
                                      ORGANIZATION    IS INDEXED
                                      RECORD KEY      IS FILE1-SEQ-KEY
                                      STATUS          IS FILE1-SEQ-STATUS.

SELECT FILE1-DYN                      ASSIGN          TO FILE1
                                      ACCESS MODE     IS DYNAMIC
                                      ORGANIZATION    IS INDEXED
                                      RECORD KEY      IS FILE1-DYN-KEY         
                                      STATUS          IS FILE1-DYN-STATUS.


Code:
FILE SECTION.

FD   FILE1-SEQ           
     DATA RECORD IS FILE1-SEQ-RECORD.
01   FILE1-SEQ-RECORD.
      10  FILE1-SEQ-KEY       PIC X(09).
      10  FILLER              PIC X(91).

FD  FILE1-DYN           
    DATA RECORD IS FILE1-DYN-RECORD.
01  FILE1-DYN-RECORD.
     10  FILE1-DYN-KEY       PIC X(09).
     10  FILLER              PIC X(91).



Code:
PROCEDURE DIVISION.
 
 OPEN FILE1-SEQ           
 OPEN FILE1-DYN   


Both open were successful.

Also when we perform the read on both files it works correctly. i.e using FILE1-SEQ, you read sequentially and using FILE1-DYN you can read file randomly.

Can anyone help me to understand concept, how this works?
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Robert Sample

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Joined: 06 Jun 2008
Posts: 8201
Location: Dubuque, Iowa, USA

PostPosted: Wed Apr 30, 2014 4:17 pm    Post subject:
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What do you not understand? You are accessing the same file multiple times in different ways simultaneously. Nothing different than accessing two different files at the same time. Remember, each file you declare in COBOL has its own record pointer and buffers so FILE1-SEQ and FILE1-DYN are accessing the file independently of one another.

Note that if you update the file you may start experiencing problems.
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