从文本文件VB.net删除一行 [英] Deleting a line from a text file VB.net

问题描述

嗨

我有一个上传文件的程序.文件上载后，用户输入项目编号，程序将读取文件，如果找到该项目，它将删除该项目所在的行.

我使用了以下代码

Hi

I have a program in which the files are uploaded. Once the file is uploaded a user enters a item number and the program reads the file and if the item is found it will delete the line if that item.

i have used the following code

Dim filepath As String = Me.Page.Server.MapPath("..\CSSN\" + files)
                               Dim lines As New List(Of String)(System.IO.File.ReadAllLines(filepath))

                               'Remove the line to delete, e.g.
                               lines.RemoveAt(count)

                               System.IO.File.WriteAllLines(filepath + ".old", lines.ToArray())

                           End If
                           count += 1
                           If StrReqline Is Nothing Then
                           Else
                               fields = StrReqline.ToString.Split((",").ToCharArray)
                           End If
 
Problem i am having is that a new file is created.
Is there any way in which i can delete the line without creating a new file?

                       End While

推荐答案

在实践中不行.文本文件只是字节的线性序列(除非您的代码对其进行处理，否则它们甚至不知道行").

要删除或插入任何内容，即使是该位置的整个文件中的单个字符也必须重写.尽管可以做到这一点-将文件指针放在插入/删除点，然后写入其余文件内容即可-为了安全起见，最好写入整个文件，然后重命名和/或删除原始文件.这样一来，故障将不会导致文件被更改一半.

如果您经常需要按行插入或删除项目，那么我将不使用文本文件-而是使用小型数据库，因为它们的组织方式可以有效地做到这一点.

Not in practice. Text files are just a linear sequence of bytes (they don''t even know about "lines" unless your code processes them to do so).

To delete or insert anything, even a single character the whole file from that point must be re-written. While that can be done - position the file pointer at the insert / delete point and write the rest of the file content will do it - for safety sake it is better to write the whole file, and then rename and / or delete the original. That way a failure will not cause the file to be half altered.

If you regularly need to insert or remove items on a "line" basis, then I would not use a text file - use a small database instead as they are organised to allow this efficiently.

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