Visual Basic.NET How to Program (PDF)

810 Files and Streams Chapter 17
99 ' get data from file if account is valid
100 Else
101
102 ' locate position in file where record exists
103 file.Seek( _
104 (accountNumber - 1) * CRandomAccessRecord.SIZE, 0)
105
106 ' read data from record
107 record.Account = binaryInput.ReadInt32()
108 record.FirstName = binaryInput.ReadString()
109 record.LastName = binaryInput.ReadString()
110 record.Balance = binaryInput.ReadDouble()
111 End If
112
113 Return record
114
115 ' notify user of error during reading
116 Catch fileException As IOException
117 MessageBox.Show("Cannot read file", "Error", _
118 MessageBoxButtons.OK, MessageBoxIcon.Error)
119
120 ' notify user of error in parameter mismatch
121 Catch formattingException As FormatException
122 MessageBox.Show("Invalid Account", "Error", _
123 MessageBoxButtons.OK, MessageBoxIcon.Error)
124
125 End Try
126
127 Return Nothing
128 End Function ' GetRecord
129
130 ' add record to file at position determined by accountNumber
131 Public Function AddRecord(ByVal record As CRandomAccessRecord, _
132 ByVal accountNumber As Integer) As Boolean
133
134 ' write record to file
135 Try
136
137 ' move file-position pointer to appropriate position
138 file.Seek( _
139 (accountNumber - 1) * CRandomAccessRecord.SIZE, 0)
140
141 ' write data to file
142 binaryOutput.Write(record.Account)
143 binaryOutput.Write(record.FirstName)
144 binaryOutput.Write(record.LastName)
145 binaryOutput.Write(record.Balance)
146
147 ' notify user if error occurs during writing
148 Catch fileException As IOException
149 MessageBox.Show("Error Writing To File", "Error", _
150 MessageBoxButtons.OK, MessageBoxIcon.Error)
Fig. 17.18 CTransaction class handles record transactions for the transactionprocessor
case study (part 3 of 4).