Using KSAM XL: 900 Series HP 3000 Computer Systems > Appendix A COBOL IntrinsicsKSAM Logical Record Pointer |
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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. Table A-1 Positioning the Logical Record Pointer
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. The file KSAMFILE illustrated in Figure A-2 “Representation of KSAMFILE Used in COBOL Examples” is used in all subsequent examples associated with the COBOL procedure calls. A File Description in Working Storage for Figure A-2 appears on the following page.
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