| View previous topic :: View next topic |
| Author |
Message |
naveen_kj
Beginner
Joined: 03 Feb 2003
Posts: 18
Topics: 8
Location: India
|
 Posted: Mon Feb 03, 2003 5:24 am Post subject: Difference between DUMMY and NULLFILE |
 |
|
 Can any one explain me the difference between "DD DUMMY" and "DD DSN=NULLFILE". At what conditions these two are used? |
|
| Back to top |
|
 |
kolusu
Site Admin
Joined: 26 Nov 2002
Posts: 12378
Topics: 75
Location: San Jose
|
| Posted: Mon Feb 03, 2003 6:54 am Post subject: |
|
|
Naveen,
As far as I know there is no difference.The resulting control blocks when opening different DCB's in Assembler are identical.The operating system action is identical in both cases, but their use in JCL is slightly different.
One use of the DUMMY parameter is in testing a program. When testing is finished and you want input or output operations performed on the data set, replace the DD DUMMY statement with a DD statement that fully defines the data set. Another use of the DUMMY parameter is in a cataloged or in-stream procedure. Code on the DD DUMMY statement all the required parameters. When the procedure is called, nullify the effects of the DUMMY parameter by coding on the DD statement that overrides the DD DUMMY statement a DSNAME parameter that matches the DSNAME parameter on the DD DUMMY statement. For example, procedure step PS contains the following:
| Code: |
//DS1 DD DUMMY,DSNAME=A,DISP=OLD
|
Nullify the DUMMY parameter by coding:
| Code: |
//JS EXEC PROC=PROC1
//PS.DS1 DD DSNAME=A
|
For a dummy data set, the system bypasses all input/output operations, does not allocate devices or storage to the data set, and does not perform disposition processing.
NULLFILE Specifies a dummy data set. NULLFILE has the same effect as coding the DD DUMMY parameter. NULLFILE must be coded as a single-word parameter.
Check the following for a detailed explanation of DUMMY Parameter
NULLFILE
Hope this helps...
cheers
kolusu |
|
| Back to top |
|
|
naveen_kj
Beginner
Joined: 03 Feb 2003
Posts: 18
Topics: 8
Location: India
|
| Posted: Mon Feb 03, 2003 8:46 am Post subject: |
|
|
thanks Kolusu  |
|
| Back to top |
|
|
slade
Intermediate
Joined: 07 Feb 2003
Posts: 266
Topics: 1
Location: Edison, NJ USA
|
| Posted: Sun Feb 09, 2003 2:59 am Post subject: |
|
|
Just a note about a nasty feature of dummy/nullfile datasets.
If you dummy a dataset in a concatenated list of input datasets and it's not the last dataset in the concatenation, the program will go to EOF and fail to process any remaining records that exist in the concatenated list.
Nasty!!! |
|
| Back to top |
|
|
|
|
|
FAQ
Search
Quick Manuals
Register
Profile
Log in to check your private messages
Log in
