如何有效地仅读取文本文件的最后一行

Question

只需要从大日志文件中获取最后一行。最好的方法是什么？

Answer 1

您想使用 ReverseLineReader 向后读取文件：

如何在 C# 中使用迭代器反向读取文本文件

然后在它上运行.Take(1)。

var lines = new ReverseLineReader(filename);
var last = lines.Take(1);

您需要直接使用 Jon Skeet 的库 MiscUtil，而不是复制/粘贴代码。

Answer 2

    String lastline="";
    String filedata;
    // Open file to read
    var fullfiledata = new FileStream(filepath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
    StreamReader sr = new StreamReader(fullfiledata);
    //long offset = sr.BaseStream.Length - ((sr.BaseStream.Length * lengthWeNeed) / 100);
    // Assuming a line doesnt have more than 500 characters, else use above formula
    long offset = sr.BaseStream.Length - 500;
    //directly move the last 500th position
    sr.BaseStream.Seek(offset, SeekOrigin.Begin);
    //From there read lines, not whole file
    while (!sr.EndOfStream)
    {
        filedata = sr.ReadLine();
        // Interate to see last line
        if (sr.Peek() == -1)
        {
            lastline = filedata;
        }
    }       
    return lastline;
}

Answer 3

或者

你可以做两行（仅限.Net 4）

var lines = File.ReadLines(path);
string line = lines.Last();