添加一个单行文本文件的顶部 [英] Add a single line to the top of text file

问题描述

我的应用程序中提取数据，并将其添加到一个文本文件，但我需要找出我如何可以通过编程的文本文件的第一行，看看它下面的文本相匹配：

  

日期时间，VirtualIP，VirtualPort，VirtualName，DestinationIP，DestPort，状态，期望

如果它不再继续执行正常功能（下面片段），如果如上述然后我要插入上述第一行中，而不覆盖最新目前存在的第一行是不一样的。我怎样才能做到这一点？ （基本上都推一条线下来，我可以加我想要在第一行）......顺便说一句，这是被保存为可以在Excel中打开CSV文件。

 尝试
{
    // ...
    对于（INT J = 0; J＆LT; memberStatus.Result.Count; J ++）
    {
        VirtualMemberStatus状态= memberStatus.Result [J]。

        //文字+ =的String.Format（名称：{4}，会员：{0}：{1}，状态：{2}，期望：{3}+ Environment.NewLine，status.Member.Address，状态.Member.Port，status.EffectiveStatus，status.DesiredStatus，virtualKey.Key）;
        文+ =的String.Format（{5}，{4}，{0}，{1}，{2}，{3}+ Environment.NewLine，status.Member.Address，status.Member.Port，状态.EffectiveStatus，status.DesiredStatus，virtualKey.Key.Replace（：，，），DateTime.UtcNow）;
    }
}
抓住
{
    //错误code 2
    //MessageBox.Show("Error发生，请检查设备名称（区分灵敏）和管理员组此错误也可能会出现由于连接丢失，请重试）。;
    错误+ =的String.Format（{0}错误code：2，发生错误，请检查也可能会出现此错误是由于连接丢失，请重试设备名称（区分灵敏）和管理员组。+环境。换行，DateTime.UtcNow）;

}

this.resultsTextBox.Text =文本;
 

该文件不被删除了很多，但在它的事件中，我希望它有顶部的正确的列名。即：

 日期时间，VirtualIP，VirtualPort，VirtualName，DestinationIP，DestPort，状态，期望
 

解决方案

您需要重写整个文件。

1. 打开一个新的（暂时的！）文件
2. 在写标题行
3. 在每个输入线，写入线（考虑块缓冲，如果性能是一个问题）
4. 刷新和关闭输出文件
5. 只有当没有错误，将临时文件就地（通过重命名）。

这过程可以prevent的问题时，有一个（IO）中途遇到错误时的过程是

下面是code做这样的事情：

 使用（VAR输入=新的StreamReader（input.txt的））
    使用（VAR输出=新的StreamWriter（input.txt.temp））
{
    output.WriteLine（headerline）; //替换为自己的头:)

    VAR BUF =新的char [4096];
    INT读= 0;
    做
    {
        读= input.ReadBlock（BUF，0，buf.Length）;
        output.Write（BUF，0，读）;
    }而（读大于0）;

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

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

请注意，样品code甚至创建一个备份。改进的一种可能的情况是将明确地实例化的FileStream（....，FileMode.CreateNew），以prevent覆盖临时文件，如果文件已经存在该名称。

另一种解决方案，这将是，使用<一href="http://msdn.microsoft.com/en-us/library/system.io.path.gettempfilename.aspx"><$c$c>System.IO.Path.GetTempFileName().但是，那么 File.Replace 可能不再有效，原子，因为tempfolder可能是另一个卷/文件系统。

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

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;

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

解决方案

You need to rewrite the whole file.

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).

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

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");

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.

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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