VB6 beginners tutorial - Learn VB6

Advanced VB6 tutorial - Learn Advanced VB6

VB .NET - Learn Visual Basic .NET

Systems Analysis - System analysis and Design tutorial for Software Engineering

Browse Topics

- Getting started
- Data Types
- Modules
- Operators in VB6
- VB6 Variable
- VB6 Procedures
- VB6 Control Structures
- Loops in VB6
- VB6 Exit Do & With End With
- Arrays in VB6
- User-Defined Data Types
- VB6 Constants
VB6 Built-in Functions
- Date and Time in VB6
- VB6 Controls
- TextBox Control
- ComboBox & OptionButton
- Label & Frame
- PictureBox & ImageBox
- Timer Control
- ListBox & ComboBox
- VB6 ScrollBar
- Control Arrays in VB6
- Files controls in VB6
- VB6 CheckBox
- Forms in VB6
- Menus in VB6
- MDI Form in VB6
- InputBox
- MessageBox
- Mouse events
- Mouse Move
- Error Handling
Error Handling (2)
VB6 Database

You are here: Visual Basic > VB6 (Beginners Tutorial)

Tutorial Main Page | Previous Page | Contents | Next Page

Random Access Files

• Note that to access a particular data item in a sequential file, you need to read in all items in the file prior to the item of interest. This works acceptably well for small data files of unstructured data, but for large, structured files, this process is time-consuming and wasteful. Sometimes, we need to access data in nonsequential ways. Files which allow nonsequential access are random access files.

• To allow nonsequential access to information, a random access file has a very definite structure. A random access file is made up of a number of records, each record having the same length (measured in bytes). Hence, by knowing the length of each record, we can easily determine (or the computer can) where each record begins. The first record in a random access file is Record 1, not 0 as used in Visual Basic arrays. Each record is usually a set of variables, of different types, describing some item. The structure of a random access file is:

• A good analogy to illustrate the differences between sequential files and random access files are cassette music tapes and compact discs. To hear a song on a tape (a sequential device), you must go past all songs prior to your selection. To hear a song on a CD (a random access device), you simply go directly to the desired selection. One difference here though is we require all of our random access records to be the same length - not a good choice on CD’s!

• To write and read random access files, we must know the record length in bytes. Some variable types and their length in bytes are:

Type          Length (Bytes)

Integer       2
Long          4
Single        4
Double      8
String         1 byte per character

So, for every variable that is in a file’s record, we need to add up the individual variable length’s to obtain the total record length. To ease this task, we introduce the idea of user-defined variables.


Tutorial Main Page | Previous Page | Contents | Next Page


Home | About Us | Privacy Policy | Contact Us

Copyright © | All Rights Reserved