Basic Input and Output Methods for VB

Lecture 11: Basic Input and Output
Methods for VB

Introduction
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So far, we have relied on GUI-based Input/Output
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By using VB controls
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For Data Input to our programs
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For Data Output from our programs:
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= Data Entry
TextBox (our basic input tool, so far)
CheckBox, OptionBox, etc
= Data Displaying
Label, message box
ListBox

However, we may also use Files for I/O
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These provide a means for long term storage of results.

Using Files for Input / Output
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Process of using files for Data I/O is called File Handling
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This requires not only methods for reading and writing data
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But also methods for Opening and Closing files

VB provides a number of pre-defined methods for File Handling

Syntax for a general file-handling „block‟ is as follows:
FileOpen( Integer file_number , String file_name , open_mode )
Some Data Processing ( e.g., writing to or reading from a file )

FileClose( file_number )
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Note: this is not a block in the formal sense (for variable scope)

FileOpen() opens a file, according to mode open_mode
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This must be done before reading or writing
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Every open file must be assigned a unique file number
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Ex: file_name = “myfile.txt”
Ex: file_number = 1

FileClose( ) closes the file, after processing job is finished.

Modes of File Handling
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Opening Files for Sequential Access
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Reading/Writing one stored text data piece at a time
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Input Mode (OpenMode.Input)
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Used to output data, to the file start

Append Mode (OpenMode.Append)
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Used to input data from file start

Output Mode (OpenMode.Output)
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Usually, elements are separated by commas (comma-delimited)

Here, we focus on the basics: sequential access.

Used to update a file (add and save)
Add sequentially, from the file end

However, note that we also have random modes of Handling Files
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Binary Mode