HOW TO: Determine whether a Sequential Access File Exists
Syntax
IO.File.Exists(fileName)
Example
If IO.File.Exists(“report.txt”) = True Then
determines whether the report.txt file exists in the current project’s bin\Debug folder.
Showing posts with label File. Show all posts
Showing posts with label File. Show all posts
Wednesday, November 3, 2010
Reading data from a Sequential Access File
HOW TO: Declare a StreamReader Variable
Syntax
{Dim | Private} streamReaderVariableName As IO.StreamReader
Example
Dim inFile As IO.StreamReader
declares a StreamReader variable named inFile.
HOW TO: Create a StreamReader Object
Syntax
IO.File.OpenText(fileName)
Example
inFile = IO.File.OpenText(“report.txt”)
opens the report.txt file for input, creates a StreamReader object and assigns it to the inFile variable.
HOW TO: Read data from a sequential access file
Syntax
streamReaderVariableName.ReadLine
Example
Dim message As String
message = inFile.ReadLine
reads a line of text from the file associated with the inFile variable and assigns the line, excluding the newline character, to the message variable.
Syntax
{Dim | Private} streamReaderVariableName As IO.StreamReader
Example
Dim inFile As IO.StreamReader
declares a StreamReader variable named inFile.
HOW TO: Create a StreamReader Object
Syntax
IO.File.OpenText(fileName)
Example
inFile = IO.File.OpenText(“report.txt”)
opens the report.txt file for input, creates a StreamReader object and assigns it to the inFile variable.
HOW TO: Read data from a sequential access file
Syntax
streamReaderVariableName.ReadLine
Example
Dim message As String
message = inFile.ReadLine
reads a line of text from the file associated with the inFile variable and assigns the line, excluding the newline character, to the message variable.
StreamWriter object
HOW TO: Declare a StreamWriter object
Syntax
{Dim | Private} streamWriterVariableName As IO.StreamWriter
Example
Dim outFile As IO.StreamWriter
declares a StreamWriter variable named outFile
HOW TO: Create a StreamWriter object
Syntax
IO.File.method(fileName)
Methods
CreateText: opens a file for output - creates a new empty file to which data can be written. If the file already exists, the data in the file is deleted before any new data is written to it.
AppendText: opens a file for append - the new data is written after any existing data in the file. If the file does not exist, the file is created for you.
Example 1
outFile = IO.File.CreateText(“mytextfile.txt”)
opens the mytextfile.txt file for output; creates a StreamWriter object and assigns it to the outFile variable. The file is open for output.
Example 2
outFile = IO.File.AppendText(“report.txt”)
opens the report.txt file for append; creates a StreamWriter object and assigns it to the outFile variable. The file is open for append.
Syntax
{Dim | Private} streamWriterVariableName As IO.StreamWriter
Example
Dim outFile As IO.StreamWriter
declares a StreamWriter variable named outFile
HOW TO: Create a StreamWriter object
Syntax
IO.File.method(fileName)
Methods
CreateText: opens a file for output - creates a new empty file to which data can be written. If the file already exists, the data in the file is deleted before any new data is written to it.
AppendText: opens a file for append - the new data is written after any existing data in the file. If the file does not exist, the file is created for you.
Example 1
outFile = IO.File.CreateText(“mytextfile.txt”)
opens the mytextfile.txt file for output; creates a StreamWriter object and assigns it to the outFile variable. The file is open for output.
Example 2
outFile = IO.File.AppendText(“report.txt”)
opens the report.txt file for append; creates a StreamWriter object and assigns it to the outFile variable. The file is open for append.
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