Random files

Opening random files

The syntax is:

Open fileName For Random As fileNumber [Len = recordLength]

where recordLength is the length of each record in the file. The default length is 128 bytes.

If the file does not exist, it is created.

Defining record types

Because records in a random file must have the same length, elements of a type should be fixed-length. If a string copied into a file record contains fewer characters than the record's fixed length, the remainder of the record is left unchanged. However, if a string is too long for a record, it is truncated when written.

String fields inside the user-defined type should also be fixed-length. If you do use variable-length, make sure that the Len part of the Open statement specifies a length large enough to hold the longest strings. The Len function can't give you a reliable value for the length of the record; you will need to estimate that. You also can't navigate between records by omitting the record number in the Get and Put statements.

User-defined types can be used to define compound records.

For example:

Type emploRec 
   id As Integer             ' Integers are 2 bytes long
   salary As Currency        ' Currency is 8 bytes
   hireDate As Double        ' Dates are also 8 bytes
   lastName As String * 15   ' Fixed-length string of 30 bytes
   firstName As String * 15  ' Fixed-length string of 30 bytes
End Type

The length of a type can be determined at run time using the Len function.

For example, this record is 78 bytes long, so supply Len = 78 in the Open statement.

Dim recLen As Integer, idFile As Integer
Dim recHold As emploRec
idFile = 1               ' The file number to use for
                         ' this file
recLen = Len(recHold)    ' The record length for this file
Open "DATA.DAT" For Random As idFile Len = recLen

Writing to random files in LotusScript®

Use the Put statement to write to a random file. Put takes three parameters: the file number, the record number, and a variable containing the data you wish to write. You can use Put to add or replace records, but not to delete them. To replace a record in a random file, use its record number.

For example:

Dim recNum As Integer
recNum = 5
' Replace record 5 with the contents of recHold.
Put idFile, recNum, recHold

To add new records to a random file, use a record number equal to one more than the number of records in the file. To add a record to a file that contains 5 records, for example, use a position of 6.

To replace a record from a random file, create a new file and copy all the valid records from the original file into the new file. Close the original file and use the Kill statement to delete it. Use the Name statement to rename the new file to the same name as the original. You can also move each record, following it "up" by one position, thus writing over the record. The problem with this technique is that it leaves a duplicate record at the end of the file.

For example:

Dim tempRec As emploRec
For I = recNum To lastRec - 1
   Get idFile, I + 1, tempRec
   Put idFile, I, tempRec
Next I 

Reading from random files

Use the Get statement to read from a random file into variables.

This example reads from the file numbered idFile, at record number 5, into the variable recHold.

' The record number to retrieve from the file
Dim recNum As Integer 
recNum = 5
' The variable to read into
Dim recHold As emploRec
Get idFile, recNum, recHold