HP 3000 Manuals HP 3000 Manuals
BKREWRITE
Changes the contents of a record in a KSAM file.
CALL BKREWRITE (filenum, status, parameterlist)
A call to BKREWRITE replaces the contents of an existing record with new
values. The record to be rewritten is the last record accessed by a call
to BKREAD, BKREADBYKEY, or BKSTART. To use BKREWRITE, the file must be
open in the access mode that allows update. If access is shared, it must
also be opened with dynamic locking allowed, and the file locked by
BKLOCK before records are rewritten.
PARAMETERS
filenum A numeric variable containing the file number that
identifies the file; this number was returned by the
last call to BKOPEN. It should not be altered unless the
file is closed with a successful call to BKCLOSE.
(Required parameter)
status A four-character string variable to which is returned a
code that indicates whether or not the call to BKREWRITE
was successful and if not, why not. The first character
is set to zero if the call succeeds, to another value if
not. (Refer to the Status Parameter discussion earlier
in this section. (Required parameter)
parameterlist A list of variables or constants, separated by commas,
that contain the data to be written to the file
replacing the last record read or written. The total
length of the new record is derived from the total
number, data type, and length in characters of each item
in parameterlist. Although this length need not be the
same as the record it replaces, it should be long enough
to contain all the keys, but not so long that it exceeds
the defined record length. (Required parameter)
USING BKREWRITE
After calling BKREWRITE, you should always check the status parameter to
make sure that the rewrite was successful. Upon successful completion of
BKREWRITE, new values replace the data in the last record read to or
written from the BASIC program. The new data may change every value in
the previously read record including the primary key value.
If you want to replace a record with a particular key value, you should
locate and read the record with BKREADBYKEY or BKSTART. To rewrite a
series of records you should read the records with BKREAD.
When the data in the parameterlist of BKREWRITE is shorter in total
length than the data in the record being rewritten, there is less total
data in the rewritten record. In order to maintain the key sequence of
all keys, defined values should be written to the location of all keys,
both the primary key and any alternate keys.
NOTE Items written to a KSAM file with the BKREWRITE procedure are
concatenated; rounding to word boundaries does not occur.
The example in Figure 6-7 writes new values to a record originally
written if Figure 6-11 and read in Figure 6-5. The new values fill an
array that had undefined values in the last five words, now defined as
two arrays A3 and A2 by the BKREAD call. The primary key value "23" in
location 2 is unchanged.
The record read by BKREAD contained the following values:
![[]](../../pic3k/M010088/F0606A3c50.gif)
After being rewritten by BKREWRITE, it contains the following values:
![[]](../../pic3k/M010088/F0606B3c50.gif)
Shared Access. When access is shared, the call to BKREAD, BKREADBYKEY,
or BKSTART that locates the record to be rewritten should be included in
the same pair of BKLOCK/BKUNLOCK calls as the call to BKREWRITE. This
insures that no other user alters the record pointer between the call
that locates the record and the call that rewrites it.
Duplicate Keys. If you want to sequentially rewrite all records in a
chain of records with duplicate keys, locate the first record in the
chain with BKREADBYKEY. Then call BKREWRITE to modify this record. If no
key value (the selected key or any other) is modified, subsequent calls
to BKREWRITE will modify the next sequential records in the chain of
duplicate keys. If, however, any key has been changed, the modified key
is written to the end of the chain and the next sequential record is one
with the next higher key value. In this case, to rewrite all records
with duplicate keys, precede each call to BKREWRITE by a call to
BKREADBYKEY.
______________________________________________________________________________
| |
| 2600 REM |
| 2610 REM ********************************************************* |
| 2620 REM * REVISE THE CONTENTS OF A RECORD READ FROM A KSAM FILE * |
| 2630 REM ********************************************************** |
| 2640 REM |
| 2650 REM F IS THE FILE NUMBER OF A KSAM FILE OPENED BY A CALL TO BKOPEN|
| 2660 REM NOTE THAT FOR BKREWRITE,BKOPEN ACCESS MODE MUST=4 FOR UPDATE. |
| 2670 REM |
| 2680 REM AN ASSUMPTION HAS BEEN MADE THAT THE RECORD TO BE READ |
| 2690 REM CONTAINS THE SAME INFORMATION THAT WAS WRITEM TO THE |
| 2700 REM KSAM FILE IN THE BKWRITE EXAMPLE,, |
| |------------------ parameterlist |
| 2710 REM /------------------------\ |
| 2720 CALL BKREAD(F,S$,B1$,B2$,A5[*],A3[*],A2[*]) |
| 2730 REM |
| 2740 REM NOW DETERMINE WHETHER THE CALL HAS SUCCEEDED. |
| 2750 REM |
| 2760 IF S$(1;1]<>"0" THEN DO |
| 2770 REM N$ CONTAINS THE NAME OF THE KSAM FILE |
| 2780 REM S$ CONTAINS THE STATUS CALL SET BY THE PRECEDING CALL |
| 2790 PRINT "UNABLE TO READ ";N$;" ERROR ";S$[1;1]" DETAIL ";S$[2] |
| 2800 CALL BKERROR(S$,M$) |
| 2810 PRINT M$ |
| 2820 GOTO 3620 |
| 2830 DOEND |
| 2900 REM THE CONTENTS OF B1=1", OF B2$="23" |
| 2910 REM THE CONTENTS OF A5(1) THROUGH A5(5) ARE 1 THROUGH 5 |
| 2920 REM THE CONTENTS OF A3 AND A2 ARE UNKNOWN |
| 2930 REM |
| 2940 REM STORE VALUES 1 THROUGH 3 INTO A3(1) THROUGH A3(3) |
| 2950 REM STORE VALUES 1 AND 2 INTO A2(1) AND A2(2). |
| 2960 REM |
| 2970 FOR I=1 TO 2 |
| 2980 A2[I]=I |
| 2990 A3[I]=I |
| 3000 NEXT I parameterlist |
| 3010 A3[3]=3 | |
| 3020 REM /------------------------\ |
| 3030 CALL BKREWRITE(F,S$,B1$,B2$,A5[*],A3[*],A2[*]) |
| 3040 REM |
| 3050 REM NOW DETERMINE WHETHER THE CALL HAS SUCCEEDED |
| 3060 REM |
| 3070 IF S$[1;1]<>"0 THEN DO |
| 3080 REM N$ CONTAINS THE NAME OF THE KSAM FILE |
| 3090 REM S$ CONTAINS THE STATUS CODE SET BY THE PRECEDING CALL |
______________________________________________________________________________
Figure 6-7. Rewriting Record in KSAM File with BKREWRITE
____________________________________________________________________________
| |
| 3100 PRINT "UNABLE TO REWRITE ";N$;" ERROR ";S$[1;1];" DETAIL ";S$[2]|
| 3110 CALL BKERROR(S$,M$) |
| 3120 PRINT M$ |
| 3130 GOTO 3620 |
| 3140 DOEND |
| 3150 REM |
| 3160 REM ECHO WHAT WAS UPDATED |
| 3170 REM |
| 3180 PRINT "REWRITTEN RECORD = ";B1;B2 |
| 3190 MAT PRINT A5,A3,A2 |
| 3200 REM |
| 3210 REM THE PROGRAM CONTINUES |
____________________________________________________________________________
Figure 6-7. Rewriting Record in KSAM File with BKREWRITE (continued)