How to: Read From Comma-Delimited Text Files in Visual Basic

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Visual Studio 2010 - Visual Basic

The TextFieldParser object provides a way to easily and efficiently parse structured text files, such as logs. The TextFieldType property defines whether it is a delimited file or one with fixed-width fields of text.

To parse a comma delimited text file

Create a new TextFieldParser. The following code creates the TextFieldParser named MyReader and opens the file test.txt.

Visual Basic


Using MyReader As New Microsoft.VisualBasic.
                      FileIO.TextFieldParser(
                        "C:\TestFolder\test.txt")

Define the TextField type and delimiter. The following code defines the TextFieldType property as Delimited and the delimiter as ",".
Visual Basic
MyReader.TextFieldType = FileIO.FieldType.Delimited MyReader.SetDelimiters(",")

Loop through the fields in the file. If any lines are corrupt, report an error and continue parsing. The following code loops through the file, displaying each field in turn and reporting any fields that are formatted incorrectly.

Visual Basic



Dim currentRow As String()
   While Not MyReader.EndOfData
      Try
         currentRow = MyReader.ReadFields()
         Dim currentField As String
         For Each currentField In currentRow
            MsgBox(currentField)
         Next
         Catch ex As Microsoft.VisualBasic.
                     FileIO.MalformedLineException
           MsgBox("Line " & ex.Message &
           "is not valid and will be skipped.")
     End Try

Close the While and Using blocks with End While and End Using.
Visual Basic
End While End Using

Example

This example reads from the file test.txt.

Visual Basic


  Using MyReader As New Microsoft.VisualBasic.
                        FileIO.TextFieldParser(
                          "C:\TestFolder\test.txt")
   MyReader.TextFieldType = FileIO.FieldType.Delimited
   MyReader.SetDelimiters(",")
   Dim currentRow As String()
   While Not MyReader.EndOfData
      Try
         currentRow = MyReader.ReadFields()
         Dim currentField As String
         For Each currentField In currentRow
            MsgBox(currentField)
         Next
      Catch ex As Microsoft.VisualBasic.
                  FileIO.MalformedLineException
        MsgBox("Line " & ex.Message &
        "is not valid and will be skipped.")
      End Try
   End While
End Using

Robust Programming

The following conditions may cause an exception:

A row cannot be parsed using the specified format (MalformedLineException). The exception message specifies the line causing the exception, while the ErrorLine property is assigned the text contained in the line.
The specified file does not exist (FileNotFoundException).
A partial-trust situation in which the user does not have sufficient permissions to access the file. (SecurityException).
The path is too long (PathTooLongException).
The user does not have sufficient permissions to access the file (UnauthorizedAccessException).

How to: Read From Comma-Delimited Text Files in Visual Basic

To parse a comma delimited text file

Tasks

Reference

Concepts