CODEWITHSUNDEEP
vb.netfilestream
user3267755
user3267755

Reputation: 1070

Reading a filestream issue

I am trying to read a file from my computer and output its contents into a literal control. It gives the error : Offset and length were out of bounds for the array or count is greater than the number of elements from index to the end of the source collection. This is my first time using FileStream and I'm not 100% about all of the syntax for VB, or if there's even a community-preferred way of reading from a file, but could somebody help me out with this error?

This is the code:

 Using fs As New FileStream(_path, FileMode.Open, FileAccess.Read)
                Try
                    Dim fileLength As Integer = CInt(fs.Length)
                    Dim buffer() As Byte = New Byte() {fileLength}
                    Dim count As Integer
                    Dim sum As Integer = 0

                    While ((count = fs.Read(buffer, sum, fileLength - sum)) > 0)
                        sum = sum + count
                    End While
                    litOutput.Text = buffer.ToString()
                Catch ex As Exception
                    'TODO: log error
                End Try
            End Using

Upvotes: 0

Views: 2441

Answers (1)

Steve
Steve

Reputation: 216273

This line is wrong

Dim buffer() As Byte = New Byte() {fileLength}

It declares an array of 1 byte in which you try to store the length of your file. Probably you have Option Strict set to Off and thus you could go away without noticing immediately the problem.

Of course, if your file is of a reasonable length and it is a simple textfile then there is no need for this loop. Just use File.ReadAllText or File.ReadLines or File.ReadAllLines, and by the way, your code read all your data in a single call because the last parameter of FileStream.Read is the quantity of bytes to read from file and the expression fileLength - sum produces a request to read all the bytes in a single call

Instead if you want to read your file in chunks of certain sizes then probably you need 

Using fs As New FileStream(path, FileMode.Open, FileAccess.Read)
    Try
        Dim chunkSize = 2000
        Dim fileLength As Integer = CInt(fs.Length)
        Dim buffer(fileLength) as Byte
        Dim blockSize(chunkSize) as Byte
        Dim count As Integer = -1
        Dim pos As Integer = 0

        While count <> 0
            count = fs.Read(blockSize, 0, chunkSize-1)
            Array.Copy(blockSize, 0, buffer, pos, count)
            pos += count
        End While

        litOutput.Text = Encoding.UTF8.GetString(buffer)
    Catch ex As Exception
        Console.WriteLine(ex.Message)
    End Try
End Using

Notice that this code assumes that your file is a Text file with UTF8 encoding.
It this is not the case then you could try with Encoding.ASCII.GetString or Encoding.Unicode.GetString

Upvotes: 1

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