Data files and databases

Data files and databases

Data files and databases

• Need a control to browse to a file• Standard controls for drive folder and list not

much use• The CommonDialogs control offers

– drive folder file browse to select file– print– font select– colour select

• But you need to add it in..

Adding components

Using the Common Dialog Control

Private Sub Command1_Click()CommonDialog1.ShowOpenMsgBox ("You selected " & CommonDialog1.FileName).. code to process FileNameEnd Sub

File open exercise

Program to browse and display graphics filesUse a common dialog control to select graphics filesSet the filter of the dialog to something like: Image files | *.bmp; *.jpg; *.jpeg | All files | *.*Display the selected image in a Picture control (see graphics)

VB data file ideas 2 modes –

• sequential (work through file start to end - character (external format))

• random (can move back and forth through file, binary (internal format) )

Sequential – write # and input#

Open "c:\walter\vb\filing\test1.dat" For Output As #1Write #1, 1, 2, 3.1, "Test1", "Test2"Close #1

Open "c:\walter\vb\filing\test1.dat" For Input As #1Input #1, x, y, z, a, bClose #1

Sequential – Print # and Line Input#Open "c:\walter\vb\filing\test1.dat" For Output As #1Print #1, 1, 2, "Test1"Close #1

Open "c:\walter\vb\filing\test1.dat" For Input As #1Line Input #1, xClose #1

MsgBox (x)

Exercise – sequential filing

1. Fill an array with 100 random integers2. Save them into a file ( write# )3. Read file back ( input# ) into a second array4. Check arrays have same content

Random

• Data in file as records• Must define size of record (fixed length good)• Can then seek to nth record • And read or write it

User-defined type (record)Private Type myRecordpayroll As Integerdepartment As Integername As String * 14End Type

fixed length string

length of record = 2 + 2 + 14 = 18 bytes

Writing to random access file

Dim emp As myRecordemp.payroll = 23emp.department = 3emp.name = "Fred"Open "c:\walter\vb\filing\test.dat" For Random As #1 Len = 18Put #1, 1, empemp.payroll = 17emp.department = 6emp.name = "John"Put #1, 2, empPut #1, 3, empClose #1

result on next slide

record position 1

Random file contents

record 1 record 2 record 3

2 bytes = integer = 23

2 bytes = 1 integer = 3

string padded with spaces to length 14

Reading Random File

Dim emp As myRecordOpen "c:\walter\vb\filing\test.dat" For Random As #1 Len = 18Get #1, 2, empClose #1MsgBox (emp.payroll & " " & emp.department & " " &_ emp.name)

read second record

Binary = random with record size 1Dim b As ByteOpen "c:\walter\vb\filing\test.dat" For Binary As #1For bytePosition = 1 To 10 Get #1, bytePosition, b Debug.Print bNextClose #1

Exercise – data file

• Using binary mode, write the characters A to Z into a file (ASCII 65 on)

• Then read them back in reverse ie byte position 26 first

• Debug.print them out

Working with a database – the hard way

Working with a database – the hard way

Working with a database – the hard way

Private Sub Command1_Click()Data1.Recordset.DeleteData1.RefreshEnd Sub

Working with a database – the wizardAddins..Addin Manager

Working with a database – the wizard

Exercise – database access

• Use Access to produce a simple database with just one table – personnel = ID name and department number (Access97 format)

• In a VB project have two forms– one with a data control, hand-coded

(explore insert delete buttons)– one created by the Data Form Wizard