How to: read from comma-delimited text files in 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

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

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

2. Define the TextField type and delimiter. The following code defines the TextFieldType property as Delimited and the delimiter as ",".

   MyReader.TextFieldType = FileIO.FieldType.Delimited
   MyReader.SetDelimiters(",")
   

3. 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.

   
   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
   

4. Close the While and Using blocks with End While and End Using.

       End While
   End Using
   

Example

This example reads from the file test.txt.

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).

See also

• Microsoft.VisualBasic.FileIO.TextFieldParser
• How to: Read From Fixed-width Text Files
• How to: Read From Text Files with Multiple Formats
• Parsing Text Files with the TextFieldParser Object
• Walkthrough: Manipulating Files and Directories in Visual Basic
• Troubleshooting: Reading from and Writing to Text Files