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Ram
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Joined: 12 Jan 2004
Posts: 53
Topics: 12
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 Posted: Thu Jul 07, 2005 12:02 am Post subject: SELECT OPTIONAL clause in FILE CONTROL SECTION |
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Hi,
I was going through one of our programs and saw the OPTIONAL clause in the file control section. I browsed a couple of COBOL manuals and this is what they had to say.
| Code: | Optional files are files that are not necessarily present each time the program is
run. You can define files opened in INPUT, I-O, or EXTEND mode as optional
by defining them with the SELECT OPTIONAL phrase in the FILE-CONTROL
paragraph of your program. |
It was mentioned that if a file does'nt exist, then it will be created with system defined attributes. Now is it similar to having a DUMMY dataset assigned to the file in the JCL ?
Also could you please let me know what is the use of defining files as OPTIONAL ?
Thanks,
Ram
Whatever you do in this life, it echoes in eternity ! |
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kolusu
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Joined: 26 Nov 2002
Posts: 12395
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Location: San Jose
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| Posted: Thu Jul 07, 2005 6:29 am Post subject: |
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Now is it similar to having a DUMMY dataset assigned to the file in the JCL ?
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Ram,
Nope. Optional files are created each time the program runs. Basically these files are used as temporary files. For ex: if you are doing an internal sort and you want to store the intermediate results of the sort , then you can use an optional file. It will be created and deleted at the end of the job.
Hope this helps...
Cheers
Kolusu
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Kolusu
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Ram
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Joined: 12 Jan 2004
Posts: 53
Topics: 12
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| Posted: Fri Jul 08, 2005 4:14 am Post subject: |
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Kolusu,
Thank you for the prompt response. The program that I was referring to had a VSAM file defined as Optional and it did not have a corresponding dd statement in the JCL. In this case will it cause any problems if I code a DUMMY dataset against the missing ddname in the JCL? I have understood that the optional file feature is helpful for intermediate storage. But in my case I cant see it serving any purpose.
Thanks,
Ram |
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pzmohanty
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Joined: 20 May 2004
Posts: 97
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Location: hyderabad, India
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| Posted: Sun Aug 13, 2006 1:46 pm Post subject: |
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Hi Kolusu,
Continuing with OPTIONAL option of SELECT clause, we can have OPTIONAL clause if a file is opened in INPUT / I-O / EXTEND mode and at the run time file gets created and also get deleted by end of program.
I am just curious to know why OPTIONAL option is not allowed with OUTPUT mode whereas it is allowed with I-O & EXTEND mode. What difference does it make.
Thanks in advance
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Priya Ranjan Mohanty
Consultant
Kanbay Software (I) pvt. Ltd.
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kolusu
Site Admin
Joined: 26 Nov 2002
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Location: San Jose
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| Posted: Sun Aug 13, 2006 7:29 pm Post subject: |
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| Quote: |
I am just curious to know why OPTIONAL option is not allowed with OUTPUT mode whereas it is allowed with I-O & EXTEND mode. What difference does it make.
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pzmohanty,
You can open the file in OUTPUT mode provided that you have the run-time option CBLQDA turned on. CBLQDA(ON) is the setting that dynamically allocates with DISP=(NEW,DELETE,DELETE) file when an output DD name is opened but missing from the TIOT.
Hope this helps...
Cheers
Kolusu
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Kolusu
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