C# 如何只追加文本文件的末尾和特定位置？

Question

我想将状态从 OK 更改为 NG，

IPen ID     Datetime                                Status
50      Wednesday, September 21, 2016 08:56:45      OK
IPen ID     Datetime                                Status
50      Wednesday, September 21, 2016 08:56:51      OK

这是我的 report.txt 文件。我的期望是我们如何使用 C# 删除最后一行？

IPen ID     Datetime                                Status
50      Wednesday, September 21, 2016 08:56:51      OK

以及如何将 OK 状态更改附加到 NG 状态？我希望的结果是这样的:

IPen ID     Datetime                                Status
50      Wednesday, September 21, 2016 08:56:45      NG

这是我的代码:

var lines = File.ReadAllLines(Fullpath);
File.WriteAllLines(Fullpath, lines.Take(lines.Length - 1).ToArray());
DisplayData(MessageType.Incoming, lines[lines.Length - 1]);

var text = new StringBuilder();

foreach (string s in File.ReadAllLines(Fullpath))
{
    text.AppendLine(s.Replace("OK", "NG"));
}

using (var file = new StreamWriter(File.Create(Fullpath)))
{
    file.Write(text.ToString());
}

此代码会将所有“OK”更改附加到“NG”。不像我想要的那样，但我想删除最后一个结果，只将最后两个结果从“OK”更改为“NG”，而不是将所有 OK 更改为 NG。对我有什么建议或解决方案吗？感谢关注和帮助。

Answer 1

由于您已经将整个文件读入内存，您可以将其转换为列表，从末尾删除，然后反向迭代以更新最后两个条目:

var lines = File.ReadAllLines(Fullpath).ToList();

// Remove as many lines as you'd like from the end
if (lines.Count > 2)
{
    lines.RemoveRange(lines.Count - 2, 2);
}

// Iterate backwards through the list until we've updated 2 (or more or less) lines
var linesUpdated = 0;

for (var i = lines.Count - 1; i >= 0 && linesUpdated < 2; i--)
{
    if (lines[i].Contains("OK"))
    {
        lines[i] = lines[i].Replace("OK", "NG");
        linesUpdated++;
    }
}

File.WriteAllLines(Fullpath, lines.ToArray());