Reads a block of data from a host file or Reality item that has been opened for sequential access.
READBLK data-var FROM seqfile-var {,blocksize} {SETTING setting-var} {ON ERROR statement(s)} [ THEN statement(s) | ELSE statement(s) ]
WHILE READBLK data-var FROM seqfile-var {,blocksize} {SETTING setting-var} {ON ERROR statement(s)} DO
data-var The name of a variable in which the data will be returned.
seqfile-var The name of a variable containing a sequential file reference (assigned via an OPENSEQ statement).
blocksize The number of bytes of data to be returned. If omitted, the record size specified in the OPENSEQ statement will be used. If neither is specified, a default size is used (the default size depends on the version of Reality and the platform on which it is running).
setting-var The name of a variable to which the return status is assigned. See Operation for details of the possible values for this variable.
statement(s) A sequence of one or more valid DataBasic statements, either separated by semicolons, or contained on separate lines and followed by an END statement.
The following details circumstances under which the different clauses are executed and the values returned in setting-var:
| Clause Executed | Reason | setting-var | STATUS() Value |
|---|---|---|---|
| THEN | Data read successfully | 0 | 0 |
| ELSE | Data read successfully, but end of item encountered | 0 | 0 |
| ON ERROR | Item opened, but not for sequential access (not opened with OPENSEQ) | B45 | 12 |
| File or item not open | B12 | 12 | |
| Invalid Block size | 2417 | 205 | |
| General file error | Error number | Error number |
Notes:
When used as the condition in a WHILE statement, the READBLK statement causes the DO clause to be executed if the read is successful, or the loop to be exited if the end of the file or item is encountered. The THEN and ELSE clauses must be omitted.
Caution
When the ELSE clause is executed or a loop exited because the end of the file or item has been reached, the data-var variable will contain any partial block from the end of the file.
OPENSEQ "/usr/pauls/qa4" TO SF1 THEN
FOR I = 1 TO 5
READBLK DATA FROM SF1,20 THEN
PRINT DATA
END ELSE
* If we hit the end of the file, the data is incomplete.
PRINT "Data corrupt"
CLOSESEQ SF1
STOP
END
NEXT I
END
CLOSESEQ SF1
This program opens the host file /usr/pauls/qa4 and saves a reference to the open file in variable SF1. If the file exists, the program then reads and displays the first 100 characters from the file, 20 characters at a time. Finally, the file is closed.
READSEQ statement, OPENSEQ statement, CLOSESEQ statement, SEEK statement, WRITESEQ statement, WRITEBLK statement, WEOFSEQ statement, DELETESEQ statement.