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reverse reading of a file

 
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sudhee_rb

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Joined: 29 Mar 2006
Posts: 34

PostPosted: Mon Apr 03, 2006 4:42 pm    Post subject: reverse reading of a file
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hi 2 all friends,
This is sudheer

I have a doubt regarding on reading a file

Can we read a file in reverse way?

Any body please clear my doubt.

thanks 4 before
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vikasc4

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Joined: 11 Dec 2005
Posts: 32

PostPosted: Mon Apr 03, 2006 4:48 pm    Post subject:
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Hi sudheer,

Yes u can read the file in reverse way, but there is a trick.............

and the trick is just first read the file in a table and then read that table in reverse order .

The size of table can be change dynamically by defining it with DEPENDING ON CLAUSE .

Regards
Vikas
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subramanianup
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Joined: 18 May 2005
Posts: 46
Location: Bangalore, INDIA

PostPosted: Fri Apr 07, 2006 2:13 pm    Post subject: Re: reverse reading of a file
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Hi sudheer and Vikas,
Reverse reading of file possible with some tricks.

For this you have to use SORT option, Introduce SEQNUM in that file and Sort the file in decending Order and then Remove Sequencial Nos and Now the File is in Reverse order

IN SORT

INREC FIELDS= < Here you have to INSERT Sequence No>
SORT FIELDS= < Here you have to Sort records on dec order of Seqnum>
OUTREC FIELDS = < After Sorting remove Sequence Number and write it in another file>

With Regards,
Subramanian UP
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priyesh.agrawal

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Joined: 28 Mar 2005
Posts: 1452
Location: Chicago, IL

PostPosted: Fri Apr 07, 2006 2:24 pm    Post subject: Re: reverse reading of a file
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http://ibmmainframes.com/viewtopic.php?t=986

Regards,
Priyesh.
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winchaat

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Joined: 23 Mar 2005
Posts: 14

PostPosted: Fri Apr 07, 2006 3:05 pm    Post subject: hi
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We have to open the input file in reverse order as shown below:
OPEN INPUT file-name1 REVERSED
REVERSED positions the file at its end; subsequent READ statements retrieve the records in reversed order.


--------------->RAG
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ranga_subham

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Joined: 01 Jul 2005
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PostPosted: Fri Apr 07, 2006 8:47 pm    Post subject:
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Hmm.......not able to understand what benefits would it provide? I believe it just proves one's technical capability rather than achieving any purpose. Is it worth debatable?
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superk

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Joined: 26 Apr 2004
Posts: 4649
Location: Raleigh, NC, USA

PostPosted: Fri Apr 07, 2006 10:48 pm    Post subject: Re: reverse reading of a file
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Ranga, I have seen this question asked many times before, usually as part of some Interview questions.

Most of the previous posts are accurate with the answer - No, not using COBOL if the data is on DASD (QSAM or VSAM). Yes, if the data is sorted in descending order first. Yes, using COBOL if the data is on TAPE. Yes, using REXX data stacks as previously shown. And finally, Yes using COBOL with the data on DASD if run within a CICS application.
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karthik1680
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Location: chennai

PostPosted: Mon Apr 10, 2006 5:09 pm    Post subject: Re: reverse reading of a file
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hi sudheer ,
this may help you.

open-statement
______________________________________________________________________________
| |
| >>__OPEN___________________________________________________________________> |
| <__________________________________________________________________ |
| <________________________________________________ | |
| >________INPUT____file-name______________________________________|_____|__>< |
| | |_____REVERSED___________________| | |
| | |______________NO__REWIND__| | |
| | |__WITH__| | |
| | <__________________________________________ | |
| |__OUTPUT____file-name________________________________|_______| |
| | |______________NO__REWIND__| | |
| | |__WITH__| | |
| | <____________ | |
| |__I-O____file-name__|________________________________________| |
| | <____________ | |
| |__EXTEND____file-name__|_____________________________________| |
| |
|______________________________________________________________________________|
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karthik1680
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PostPosted: Mon Apr 10, 2006 5:12 pm    Post subject: Re: reverse reading of a file
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hi
check this link
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superk

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Joined: 26 Apr 2004
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Location: Raleigh, NC, USA

PostPosted: Mon Apr 10, 2006 5:43 pm    Post subject: Re: reverse reading of a file
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karthik1680, I wish you had posted ALL of the information regarding the OPEN statement, especially the footnote for the REVERSED and NO REWIND parameters, as documemted here:

Quote:

REVERSED

Valid only for sequential single-reel files. REVERSED is not valid for VSAM files.

If the concept of reels has no meaning for the storage medium (for example, a direct access device), the REVERSED and NO REWIND phrases do not apply.
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