Visual Basic 6 Black Book
(Publisher: The Coriolis Group)
Author(s): Steven Holzner
ISBN: 1576102831
Publication Date: 08/01/98

Chapter 17
File Handling And File Controls

If you need an immediate solution to:

Using The Common Dialogs File Open And File Save As

Creating A File

Getting A File’s Length

Opening A File

Writing To A Sequential File

Writing To A Random Access File

Writing To A Binary File

Reading From Sequential Files

Reading From Random Access Files

Reading From Binary Files

Accessing Any Record In A Random Access File

Closing A File

Saving Files From Rich Text Boxes

Opening Files In Rich Text Boxes

Saving Files From Picture Boxes

Opening Files In Picture Boxes

Using The Drive List Box Control

Using The Directory List Box Control

Using The File List Box Control

Creating And Deleting Directories

Changing Directories

Copying A File

Moving A File

Deleting A File

When Was A File Created? Last Modified? Last Accessed?

Creating A TextStream

Opening A TextStream

Writing To A TextStream

Reading From A TextStream

Closing A TextStream

In Depth

This chapter focuses on file handling and using the file controls in Visual Basic. Here, we’ll see how to:

•  Use the Common Dialogs File Open and File Save As (you can find more information on this topic in Chapter 11).

•  Create a file

•  Open a file

•  Read from a file

•  Write to a file

•  Close a file

•  Read and write files with rich text boxes

•  Use the file controls like the directory list box and drive list box

•  Determine a file’s creation date, last modified date, and more

•  Move and copy files

•  Use the TextStream object

There are three main ways to access files in Visual Basic: as sequential files, as random access files, and as binary files (you set the way you’ll treat a file when you open it). We’ll get an overview of these types of files before turning to the Immediate Solutions.

Sequential Access Files

Sequential files are like tape cassettes—you read data from them in a sequential manner. If you want data at the end of the file, you have to read all the intervening data first. Sequential files are often organized into text strings in Visual Basic. Here are the Visual Basic statements and functions you use with sequential files (the # symbol refers to an open file, as we’ll see):

•  Open

•  Line Input #

•  Print #

•  Write #

•  Input$

•  Input #

•  Close

In addition, Visual Basic supports TextStream objects to make working with sequential files easier, as we’ll see later in this chapter. Here are the major TextStream methods:

•  Read

•  ReadAll

•  ReadLine

•  Write

•  WriteBlankLines

•  WriteLine

•  Close

When do you use sequential files? If you’ve got a text file full of variable-length strings, you usually treat that file as sequential. You can also use sequential files to store binary-format items like numbers.

Random Access Files

If sequential files are like cassettes, random access files are more like CDs. Random files are organized into records (usually of the same length), and you can read a particular record without having to read all the intervening data—you can move to that record in a file directly, just as you can move to a CD track.

Here are the Visual Basic statements and functions you use with random access files:

•  Type…End Type (to create and format records)

•  Open

•  Put #

•  Len

•  Seek

•  LOC

•  Get #

•  Close

When do you use random access files? If you want to create your own database files, formatted as you want them, you’d organize them into records. In fact, any file that you want to organize into records is best formatted as a random access file.

Binary Files

Binary files are simply unformatted binary data, and Visual Basic does not interpret (such as looking for text strings) or organize the contents (into records) of such files at all. These files are just bytes to Visual Basic, and the statements and functions you usually use with these files include the following:

•  Open

•  Get

•  Put

•  Seek

•  Close

Binary files include EXE files, graphics files, and so on.

The FileSystemObject

Besides the preceding file types, Visual Basic includes the FileSystemObject for easy file manipulation on disk. This object includes a number of methods for copying, moving, and deleting files such as these:

•  GetFile

•  CopyFile

•  DeleteFile

•  MoveFile

•  FileExists

•  CreateFolder

•  CreateTextFile

•  OpenTextFile

In fact, you use the FileSystemObject to create TextStream objects (with methods like CreateTextFile and OpenTextFile). We’ll see more about this topic later in this chapter.

That’s it for the overview of files and file handling. It’s time to turn to the Immediate Solutions.

Immediate Solutions

Using The Common Dialogs File Open And File Save As

The usual way to start working with files is to get a file name from the user using the Common Dialogs File Open or File Save As. We’ve covered these dialogs in depth in Chapter 11, but we’ll provide a quick overview here.

You display the File Open and File Save As dialog boxes with the Common Dialog control’s ShowOpen and ShowSave methods. These methods need no arguments passed to them—to set various options, you set the Common Dialog control’s Flags property (see Chapter 11). You can also set the Filter property so the dialog box displays only certain types of files, such as text files.