READVU

The READVU statement allows a program to read a specific field in a record in a previously opened file into a variable. It also respects record locking and locks the specified record for update.

COMMAND SYNTAX

READVU variable1 FROM { variable2,} expression1, expression2 {SETTING setvar} {ON ERROR statements} {LOCKED statements} THEN|ELSE statements

SYNTAX ELEMENTS

variable1 is the identifier into which the record will be read.

variable2, if specified, should be a jBC variable that has previously been opened to a file using the OPEN statement. If variable2 is not specified then the default file is assumed.

expression1 should evaluate to a valid record key for the file.

expression2 should evaluate to a positive integer number. If the number is invalid or greater than the number of fields in the record, then a NULL string will be assigned to variable1. If the number is 0 then the value returned in variable1 is controlled by the readv0 emulation setting. If a non-numeric argument is evaluated a run time error will occur.

If the SETTING clause is specified and the read fails, setvar will be set to one of the following values:

Incremental File Errors

If ON ERROR is specified, the statements following the ON ERROR clause will be executed for any of the above Incremental File Errors except error 128.

NOTES

If the record could not be read because another process already had a lock on the record then one of two actions is taken. If the LOCKED clause was specified in the statement then the statements dependant on it are executed. If no LOCKED clause was specified then the statement blocks (hangs) until the lock is released by the other process.

If the statement fails to read the record then any statements associated with the ELSE clause are executed. If the statement successfully reads the record then the statements associated with any THEN clause are executed. Either or both of the THEN and ELSE clauses must be specified with the statement.

The lock taken by the READVU statement will be released by any of the following events:

• The record is written to by the same program with WRITE, WRITEV, MATWRITE or DELETE statements.
• The record lock is released explicitly using the RELEASE statement.
• The program stops normally or abnormally.
• When a file is OPENed to a local file variable in a subroutine then the file is closed when the subroutine RETURNS so all locks taken on that file are released, including locks taken in a calling program. Files that are opened to COMMON variables are not closed so the locks remain intact.

See also: WRITE, WRITEU, MATWRITE, MATWRITEU, RELEASE, DELETE

For more detailed information on record locking, see the article The Keys to Record Locking.

EXAMPLES

OPEN "Customers" ELSE ABORT 201, "Customers"
OPEN "DICT Customers" TO DCusts ELSE
    ABORT 201, "DICT Customers"
END
LOOP
    READVU Rec FROM DCusts, "Xref",7 LOCKED
        CRT "Locked - retrying"
        SLEEP 1; CONTINUE ;* Restart LOOP
    END THEN
        READ DataRec FROM Rec ELSE
            ABORT 202, Rec
        END
        BREAK ;*leave the LOOP
    END ELSE
        ABORT 202, "Xref"
    END
REPEAT

jBC