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How to: Read Characters from a String

The following code examples show how to read characters synchronously and asynchronously from a string.

This example reads 13 characters synchronously from a string, stores them in an array, and displays those characters. It then reads the remaining characters in the string, stores them in the array starting at the sixth element, and displays the contents of the array.

Imports System
Imports System.IO

Public Class CharsFromStr
    Public Shared Sub Main()
        Dim str As String = "Some number of characters" 
        Dim b(str.Length) As Char 

        Using sr As StringReader = New StringReader(str)
            ' Read 13 characters from the string into the array.
            sr.Read(b, 0, 13)

            ' Read the rest of the string starting at the current string position. 
            ' Put in the array starting at the 6th array member.
            sr.Read(b, 5, str.Length - 13)
        End Using 
    End Sub 
End Class 
' The example has the following output: 

' Some number o 
' Some f characters

The next example reads all the characters asynchronously from a TextBox control, and stores them in an array. It then asynchronously writes each letter or white space character on a separate line followed by a line break to a TextBlock control.

Imports System.IO
Imports System.Text

Class MainWindow

    Private Async Sub ReadButton_Click(sender As Object, e As RoutedEventArgs)
        Dim charsRead As Char() = New Char(UserInput.Text.Length) {}
        Using reader As StringReader = New StringReader(UserInput.Text)
            Await reader.ReadAsync(charsRead, 0, UserInput.Text.Length)
        End Using 

        Dim reformattedText As StringBuilder = New StringBuilder()
        Using writer As StringWriter = New StringWriter(reformattedText)
            For Each c As Char In charsRead
                If Char.IsLetter(c) Or Char.IsWhiteSpace(c) Then
                    Await writer.WriteLineAsync(Char.ToLower(c))
                End If 
        End Using
        Result.Text = reformattedText.ToString()
    End Sub 
End Class
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