CKSTART

USING CKSTART

When CKSTART is executed, the key file is searched for the first key in the set of keys at location keyloc whose value when compared with key satisfies the comparison specified by relop. The current record pointer is positioned to the beginning of the record in the data file associated with the key found by CKSTART.

The specified length of key (key length) may be less than the length of the key in the file; if so, the comparison proceeds as if the file key were truncated on the right to the same length as key length.

If no record can be found whose key value satisfies the comparison, an invalid key condition is returned to status; that is, status is set to "23".

SHARED ACCESS. If you use CKSTART to position the pointer before reading or updating the file sequentially in a shared environment, you must lock the file with a call to CKLOCK before calling CKSTART. Then, after you have completed the sequential operations, you can unlock the file with a call to CKUNLOCK. If you wait to lock the file until after the call to CKSTART, another user can change the structure of the key file so that the position of the pointer becomes invalid for any subsequent call to a procedure that depends on the pointer position. (Refer to Table 3-3 “Positioning the Logical Record Pointer” for a list of the pointer-dependent procedures.)

EXAMPLES

Four new items must be added to the WORKING-STORAGE SECTION in Figure 3-2 Representation of KSAMFILE Used in COBOL Examples; otherwise, the same WORKING-STORAGE SECTION is used. The new items are:

   77       RELOP      PIC S9(4). COMP. 
   77       KEYVAL     PIC X(20). 
   77       KEYLOC     PIC S9(4)  COMP. 
   77       KEYLENGTH  PIC S9(4)  COMP. 

Each of these items is assigned the value appropriate to the operation to be performed by statements in the PROCEDURE DIVISION. Note that the length of array KEYVAL can be made shorter by assigning a value less than 20 to KEYLENGTH but it cannot be made longer than 20 characters. Since there is no key in KSAMFILE longer than 20 characters, this allows comparison to be made on the longest key.

The following example shows the statements needed to display the records in KSAMFILE in order by the alternate key PHONE that starts in location 23 and has a length of 8 characters. It assumes the file is open for input or input-output and that access mode is sequential. It also assumes the FINISH procedure from the CKCLOSE example.