Use of COMP SYNC clause in COBOL

sghosh · New User Joined: 13 May 2008 Posts: 2 Location: Kolkata

Hi,

Before posting this message I searched this site for similar posts but did not find any.

How and when do I use the COMP SYNC clause while declaring vairables?

Would be great if someone can tell me if this was dealt with in this forum before and let me know the link to that post.

Regards
Ghosh

enrico-sorichetti · Posted: Wed May 14, 2008 1:57 pm

the SYNC attribute is related to the way storage for variables is allocated,

the alignment boundaries are

BYTE for strings and equivalent data ( packed and pic things )
HALFWORD for 2 bytes binary numbers
FULLWORD for 4 bytes binary numbers
DOUBLEWORD for 8 bytes things

search the net for "COBOL ALIGNMENT RULES IBM" an You will find lots of links

or more simply click on the manuals link at top of the page and scroll to the cobol section

just a bit of history

one upon a time the operand boundaries were strictly enforced by hardware
an You would get a specification exception trying to use operands with the wrong alignment
- everything was done to save addressing cycles

now everything has been relaxed and alignment is not usually needed any longer

somebody will tell You when to use the SYNC attribute

sri_mf · Active User Joined: 31 Aug 2006 Posts: 218 Location: India

ksk · Posted: Wed May 14, 2008 2:53 pm

Hi,

The SYNCHRONIZED clause explicitly aligns COMP and INDEX data items along their natural WORD boundaries.

If there is no SYNCHRONIZED clause the data items are aligned on byte boundaries.

This clause is used to optimise speed of processing - but it does so at the expense of storage.

COMP SYNC (1 TO 4 Digits) = 2 Byte boundary
COMP SYNC (5 TO 9 Digits) = 4 Byte boundary
COMP SYNC (10 TO 18 Digits) = 8 Byte boundary
INDEX = 4 Byte boundary

KSK

mytags · New User Joined: 28 Apr 2008 Posts: 63 Location: US

HI
By mentioning Sync clause along with declarion we can make sure that the variable got stored in system from the starting position of the storage.
Like 2 byte or 4 bytes boundaries.We only need to menton as SYNC along with the declaration of the variable in working storage.
But usage of sync clause is actually a wastage in case of storage.
Hari.

sghosh · New User Joined: 13 May 2008 Posts: 2 Location: Kolkata

Thanks a lot everyone for all the information. :)

mmwife · Super Moderator Joined: 30 May 2003 Posts: 1592

Just 1 note of caution: if you specify SYNC in variables in a non 01 level group item, then move it to another group, those fields may not be SYNCed properly.

May be a good idea to SYNC both groups.