Read Random-Access Disk File Seek Read-Only File Sharing

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VB.NET source code showing how to open a disk file for random-access in read-only / share mode. Shows how to seek from file origin, current position, or end of file.

    Private Sub Button5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button5.Click

        ' Open an already-existing file for read-only.  Allow other
        ' processes to open the file while we have it open.
        Dim fs As New FileStream("test.dat", FileMode.Open, FileAccess.Read, FileShare.Read)

        ' Set the file pointer to 100 bytes from the beginning.
        fs.Seek(100, SeekOrigin.Begin)

        ' Set the file pointer to the end of file.
        ' There's no point in doing this when we open the file read-only.
        ' But if you are opening the file read-write, this may be something
        ' of interest.
        fs.Seek(0, SeekOrigin.End)

        ' Set the file pointer to 100 bytes beyond the current position.
        fs.Seek(100, SeekOrigin.Current)

        ' Set the file pointer to 100 bytes from the beginning.
        fs.Seek(100, SeekOrigin.Begin)

        ' Read 100 bytes at this position.
        Dim byteArray(100) As Byte
        Dim numBytesRead As Integer = fs.Read(byteArray, 0, 100)

        fs.Close()

    End Sub