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gauthaman_mech · Posted: Mon Nov 28, 2005 2:20 am Post subject: External declaration in Cobol

I have some doubts while defining a variable as external in Cobol.

Suppose I have a Main program A which calls a sub-program B. This main program uses a variable WS-TXT whcih is defined in a copybook as EXTERNAL.
Now the main program A and sub-program B will be able to use this variable WS-TXT.

Assume that I have another Main program C which calls a sub-program D. This main program C also uses the same copybook variable WS-TXT defined as EXTERNAL. Also C and D can access this variable WS-TXT.
Assume that both run as different jobs at the same time.

My question is that will this varible WS-TXT be created only once and stored in the common area for both these Main programs or will there be 2 different copies of WS-TXT in each address space and each program will access its own copy. Any change to the value of WS-TXT caued by one program will not affect the other program.

Could you please clarify the same.

Thanks

Gauthaman

kolusu · Posted: Mon Nov 28, 2005 5:47 am Post subject:

gauthaman_mech,

If WS-TXT has the same declaration in both pgm's A and C , then it is created only once and it can be referenced by both the programs.

Check these links which explains in detail about sharing data using external clause.

http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/IGY3PG10/4.2.5?DT=20020923143836

http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/IGY3LR10/5.3.7?DT=20020920180651

Hope this helps...

Cheers

Kolusu
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gauthaman_mech · Posted: Mon Nov 28, 2005 6:06 am Post subject:

Thanks a lot Kolusu.

I have only one more question.
The links say that the variable will be common for that run unit.
What does this run unit mean.
Does it mean a Run JCL which invokes a series of procedures which in turn invoke programs.
Or does it mean a program and its sub programs.

Further if this External variable was used by a cobol program and also by another independent DB2 cobol program, and the DB2 cobol program is excuted from IMS environment, there should be 2 copies of that varible even though both the programs are executed at the same time.
Am I right.

Please correct me if I am wrong.

Thanks