Visual Basic.NET How to Program (PDF)

794 Files and Streams Chapter 17
17.8 Creating a Random-Access File
Consider the following problem statement for a credit-processing application:
Create a transaction-processing program capable of storing a maximum of 100 fixed-length
records for a company that can have a maximum of 100 customers. Each record consists of
an account number (that acts as the record key), a last name, a first name and a balance.
The program can update an account, create an account and delete an account.
The next several sections introduce the techniques necessary to create this credit-processing
program. We now discuss the program used to create the random-access file that the
programs of Fig. 17.16 and Fig. 17.17 and the transaction-processing application use to
manipulate data. Class FrmCreateRandomAccessFile (Fig. 17.15) creates a random-access
file.
1 ' Fig. 17.15: CreateRandomAccessFile.vb
2 ' Creating a random file.
3
4 ' Visual Basic namespaces
5 Imports System.IO
6 Imports System.Windows.Forms
7
8 ' Deitel namespaces
9 Imports BankLibrary
10
11 Public Class CCreateRandomAccessFile
12
13 ' number of records to write to disk
14 Private Const NUMBER_OF_RECORDS As Integer = 100
15
16 ' start application
17 Shared Sub Main()
18
19 ' create random file, then save to disk
20 Dim file As CCreateRandomAccessFile = _
21 New CCreateRandomAccessFile()
22
23 file.SaveFile()
24 End Sub ' Main
25
26 ' write records to disk
27 Private Sub SaveFile()
28
29 ' record for writing to disk
30 Dim blankRecord As CRandomAccessRecord = _
31 New CRandomAccessRecord()
32
33 ' stream through which serializable data is written to file
34 Dim fileOutput As FileStream
35
36 ' stream for writing bytes to file
37 Dim binaryOutput As BinaryWriter
Fig. 17.15 FrmCreateRandomAccessFile class create files for random-access
file-processing applications (part 1 of 3).