Using KSAM/XL and KSAM 64 (32650-90886)

Appendix A 183
COBOL Intrinsics
KSAM Logical Record Pointer
KSAM Logical Record Pointer
Many of the KSAM procedures use a logical record pointer to indicate the current
record in the file. This pointer points to a key value in the index area that identifies the
current record in the data area. The particular key used, if the file has more than one key,
is the key specified in the current procedure or the last procedure that referenced a key.
Procedures that use pointers are either
pointer-dependent or pointer-independent .
Pointer-dependent procedures expect the pointer to be positioned at a particular record in
order to execute correctly. Pointer-independent procedures, on the other hand, execute
regardless of where the pointer is positioned and, in most cases, they position the pointer.
Shared Access
Particular care must be taken when using the logical record pointer during shared access
(the file was opened with CKOPENSHR). If more than one user opens the same file, one user
may modify the record pointer. This causes other users to access the data record.
To avoid this problem, you should always lock the file in a shared environment before
calling a procedure that sets the pointer and leave the file locked until all procedures that
depend on the pointer have been executed. Thus, if you want to read the file sequentially,
delete a record, or modify a record, you should lock the file, call a procedure that sets the
pointer (such as CKSTART), and then call CKREAD, CKDELETE, or CKREWRITE. When the
operation is complete, you can then unlock the file to give other users access to it.
Table A-1. Positioning the Logical Record Pointer
Procedure Name Pointer-
Dependent
Position of Pointer After Execution of Procedure
CKSTART NO Points to key whose value was specified in call.
CKREADBYKEY NO Points to key whose value was specified in call.
CKWRITE NO Points to key whose value is next in key sequence to key value
in record just written.
CKREAD YES Pointer remains positioned to key value for record just read;
unless next call is to CKREAD, or to CKREWRITE followed by
CKREAD, in which case, next CKREAD moves pointer to next
key in key sequence before reading the record.
CKDELETE YES Points to next key value in ascending sequence following key
value in record just deleted.
CKREWRITE YES
(sequential
mode)
NO
(random or
dynamic
mode)
Pointer remains positioned to key value for record just
modified, unless any key value in record was changed; in this
case, it points to next key in ascending sequence after the key
in the modified record.