在文本文件的顶部添加一行 [英] Add a single line to the top of text file

问题描述

我的应用程序拉取数据并将其附加到文本文件，但我需要了解如何以编程方式查看文本文件的第一行，看看它是否与以下文本匹配：

My app pulls data and appends it to a text file but I need to find out how I can programmatically look at the first line of the text file and see if it matches the following text:

DateTime，VirtualIP，VirtualPort，VirtualName，DestinationIP，DestPort，Status，Desired

DateTime,VirtualIP,VirtualPort,VirtualName,DestinationIP,DestPort,Status,Desired

如果它然后继续做正常的功能（下面的代码段），如果第一行与上面不一样，那么我想插入上面的第一行，而不覆盖目前在那里的什么。我如何做到这一点？ （基本上推一切一行，所以我可以添加我想要的第一行）... btw这是保存为csv文件，可以在excel中打开。

If it does then continue doing the normal function (snippet below), if the first line is not the same as above then I want to insert the above in the first line without overwriting whats currently there. How can I do this? (essentially pushing everything one line down so I can add what I want on the first line)...btw this is being saved as a csv file that can be opened in excel.

try
{
    // ...
    for (int j = 0; j < memberStatus.Result.Count; j++)
    {
        VirtualMemberStatus status = memberStatus.Result[j];

        //text += String.Format("Name: {4}, Member: {0}:{1}, Status: {2}, Desired: {3}" + Environment.NewLine, status.Member.Address, status.Member.Port, status.EffectiveStatus, status.DesiredStatus, virtualKey.Key);
        text += String.Format("{5},{4},{0},{1},{2},{3}" + Environment.NewLine, status.Member.Address, status.Member.Port, status.EffectiveStatus, status.DesiredStatus, virtualKey.Key.Replace(":", ","), DateTime.UtcNow);
    }
}
catch
{
    //ERROR CODE 2
    //MessageBox.Show("Error occurred, check device name (case senstive) and admin group. This error may also occur due to connection loss, try again.");
    errors += String.Format("{0} Error Code: 2, Error occurred, check device name (case senstive) and admin group. This error may also occur due to connection loss, try again." + Environment.NewLine, DateTime.UtcNow);

}

this.resultsTextBox.Text = text;

此文件不会被删除很多，但如果它是我想要它有正确的列名称在顶部。即：

This file does not get deleted a lot but in the event that it does I want it to have the correct column names at the top. ie:

DateTime,VirtualIP,VirtualPort,VirtualName,DestinationIP,DestPort,Status,Desired

推荐答案

您需要重写整个文件。

You need to rewrite the whole file.

1. 开启新的（临时的）档案


2. 撰写标题行
$ b

3. 刷新并关闭输出文件


4. 每个输入行都有$ b
5. 如果没有错误，请立即移动临时文件（通过重命名）。

1. open a new (temporary!) file
2. write header line
3. for each input line, write line (consider block buffering if performance is a concern)
4. flush and close output file
5. ONLY if there were no errors, move the temporary file in-place (by renaming).

此过程可以防止出现问题（IO）错误的过程

This procedure can prevent problems when there is an (IO) error halfway the process

这里是执行这样的事情的代码：

Here is code to do such a thing:

using (var input = new StreamReader("input.txt"))
    using (var output = new StreamWriter("input.txt.temp"))
{
    output.WriteLine("headerline"); // replace with your header :)

    var buf = new char[4096];
    int read = 0;
    do 
    {
        read = input.ReadBlock(buf, 0, buf.Length);
        output.Write(buf, 0, read);
    } while (read > 0);

    output.Flush();
    output.Close();
    input.Close();
}

File.Replace("input.txt.temp", "input.txt", "input.txt.backup");

请注意，示例代码甚至创建了一个备份。一个可能的改进点是明确实例化 FileStream（....，FileMode.CreateNew），以防止覆盖临时文件，如果该名称已存在的文件。

Note that the sample code even creates a backup. One possible point of improvement would be to explicitely instantiate FileStream(...., FileMode.CreateNew) so as to prevent overwriting the temporary file if a file already exists by that name.

另一种解决方案是使用 System.IO.Path.GetTempFileName（） 。但是， File.Replace 可能不再有效和原子，因为临时文件夹可能位于另一个卷/文件系统上。

Another solution to that would be, to use System.IO.Path.GetTempFileName(). However, then File.Replace might no longer be efficient and atomic, because the tempfolder might be on another volume/filesystem.

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