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FREADC
INTRINSIC NUMBER 305
Reads a logical record in chronological sequence from KSAM file to user's
stack.
I IV LA IV
lgth:=FREADC(filenum,target,tcount);
FREADC reads a logical record in chronological sequence. Chronological
sequence means the sequence in which the records were originally written
to the data file.
When FREADC is executed, the key file is not accessed. This read is
similar to the standard FREAD for non-KSAM files except that FREADC skips
any data records that are marked for deletion. Following execution, the
chronological pointer remains positioned at the same record.
FUNCTIONAL RETURN
The FREADC intrinsic returns a positive integer value to lgth showing the
length of the information transferred. If the tcount parameter in the
FREADC call is positive, the positive value returned represents a word
count; if the tcount parameter is negative, the positive value returned
is a byte count.
PARAMETERS
filenum integer by value (required)
A word identifier supplying the file number of the file
to be read in chronological sequence.
target logical away (required)
An array to which the record is to be transfered. This
array should be large enough to hold all the information
to be transferred.
tcount integer by value (required)
An integer specifying the number of words or bytes to be
transferred. If this value is positive, it signifies
the length in words; if negative, it signifies the
length in bytes; if zero, no transfer occurs.
If tcount is less than the size of the record, only the
first tcount words are transfered from the record. If
tcount is larger than the physical record size, transfer
is limited to the length of the physical record.
CONDITION CODES
CCE The information was read.
CCG The logical end-of-data was encountered during reading.
CCL The information was not read because an error occurred.
USING FREADC
This intrinsic allows you to read the records in the data file in the
order in which they are physically stored in the file. The end-of-data
is encountered following the last record in the file. If any records
have been marked for deletion (refer to the FREMOVE intrinsic), these
records are not read; otherwise, this intrinsic reads the data from the
data file exactly as it was stored.
Following execution of FREADC, the chronological pointer remains
positioned at the record just read, unless it is followed by another call
to FREADC. In a series of calls to FREADC, the pointer is advanced
automatically so you can read the file in chronological sequence without
resetting the pointer for each record.
Because FUPDATE only checks the logical pointer, you cannot update a
record located by FREADC or FREADDIR. To update a record located by its
chronological record number, you must precede the call to FUPDATE with a
call to FPOINT. Unlike FREADC or FREADDIR, FPOINT sets the logical
pointer as well as the chronological pointer.
In Figure 4-9, the FREADC intrinsic is used to read the data from the
KSAM data file in chronological order. Compare this order to the
sequential order by primary key in which the same file is read by FREAD.
(Refer to Figure 4-10 for an example showing the chronological record
number printed in association with each record listed in sequential key
order.)
SHARED ACCESS. Because FREADC is a chronological pointer-dependent
procedure, you must call one of the procedures that position the pointer
before calling FREADC. (Refer to Table 4-2 for a list of the
pointer-dependent and pointer-independent procedures.) When access is
shared, it is essential that you lock the file before calling the
procedure that positions the pointer, and then leave the file locked
while it is being read by FREADC. This insures that no other user changes
the information in the record.
For example, the following sequence of calls guarantees that you will
read the file in chronological sequence starting with a specified record
number:
FLOCK <----------- lock file
FPOINT <------------- position the chronological pointer
FREADC loop <----------------- read records in chronological sequence
FUNLOCK <--------------- unlock file
______________________________________________________________________________
| |
| $CONTROL MAIN=JEXAMPL4 |
| <<*********************************************************>> |
| <<* *>> |
| <<* EXAMPLE 4 *>> |
| <<* READ A KSAM FILE CHRONOLOGICALLY *>> |
| <<* *>> |
| <<*********************************************************>> |
| INTEGER FILNUM; |
| INTEGER LENGTH; |
| INTEGER ERRORCODE; |
| BYTE ARRAY FILENAME(0:9):="JEXAMFIL "; |
| ARRAY MESSAGE (0:35); |
| ARRAY INPUT(0:39); |
| ARAY OUTPUT(*)=INPUT; |
| INTRINSIC FOPEN,FCLOSE,FREADC,FCHECK,FERRMSG,PRINT,TERMINATE; |
| <<************************>> |
| <<* OPEN THE KSAM FILE *>> |
| <<************************>> |
| FILNUMI=FOPEN(FILNAME,3); <<OPEN THE KSAM FILE>> |
| IF FILNUM=0 |
| THEN BEGIN |
| MOVE MESSAGE:="CANNOT OPEN KSAM FILE"; |
| PRINT(MESSAGE,-21,0); |
| FCHECK(FILNUM,ERRORCIDE); <<GET THE ERROR NUMBER>> |
| FERRMSG(ERRORCODE,MESSAGE,LENGTH):<<GET MESSAGE STRING>> |
| PRINT(MESSAGE,-LENGTH,0); <<PRINT ERROR MESSAGE>> |
| TERMINATE; |
| END; |
| L1; |
| <<****************************************************>> |
| <<* READ KSAM ACCORDINGTO CHRONOLOGICAL ORDER *>> |
| <<****************************************************>> |
| FREADC(FILNUM,INPUT,-72); |
| IF > |
| THEN BEGIN <<END OF FILE>> |
| FCLOSE(FILNUM,0,0); <<CLOSE THE KSAM FILE>> |
| IF <> |
| THEN BEGIN |
| MOVE MESSAGE:="CANNOT CLOSE KSAM FILE"; |
| PRINT(MESSAGE,-22,0); |
| FCHECK(FILNUM,ERRORCODE); <<GET THE ERROR NUMBER>> |
| FFERRMSG(ERRORCODE,MESSAGE,LENGTH);<<GET MESSAGE STRING>>>|
| PRINT(MESSAGE,-LENGTH,0); <<PRINT ERROR MESSAGE>> |
| END; |
| TERMINATE; |
| END; |
______________________________________________________________________________
Figure 4-9. FREADC Example
_____________________________________________________________________
| |
| IF < |
| THEN BEGIN |
| MOVE MESSAGE:="ERROR OCCURRED WHILE READING KSAM FILE";|
| PRINT(MESSAGE,-37,0); |
| TERMINATE; |
| END; |
| <<***********************************************>> |
| <<* WRITE THE DATA JUST READ FROM KSAM FILE *>> |
| <<***********************************************>> |
| PRINT(OUTPUT,-72,0); |
| <<************************************>> |
| <<* GO BACK TO GET ANOTHER RECORD *>> |
| <<************************************>> |
| GO TO L1; |
| END; |
| |
| Output from Program Execution: |
| |
| |
| NOLAN JACK 923-4975 967 REED AVE. SUNNYVALE CA. 94087 |
| HOSODA JOE 227-8214 1180 SAINT PETER CT. LOS ALTOS CA. 94022 |
| ECKSTEIN LEO 287-5137 5303 STEVENS CREEK SANTA CLARA CA. 95050|
| CARDIN RICK 578-7015 11100 WOLFE ROAD CUPERTINO CA. 94053 |
| PASBY LINDA 295-1187 TOWN & CNTRY VILLAGE SAN JOSE CA. 94102 |
| SEELY HENRY 293-4220 1144 LEBERTY ST. EL CERRITO CA. 94053 |
| ROBERT GERRY 259-5535 12345 TELEGRAPH AVE. BERKELEY CA. 90871 |
| TURNEWR IVAN 984-8498 22905 EMERSON ST. OAKLAND CA. 98234 |
| WHITE GORDON 398-0301 4350 ASHBY AVE. BERKELEY CA. 91234 |
| WESTER ELDER 287-4598 1256 KINGFISHER ST. SUNNYVALE CA. 43098 |
| |
| END OF PROGRAM |
_____________________________________________________________________
Figure 4-9. FREADC Example (continued)