如何高效地读取文本文件的最后一行

Question

需要从大日志文件中取得最后一行。什么是最好的方式来做到这一点？

Answer 1

你想读的向后使用ReverseLineReader文件：

How to read a text file reversely with iterator in C#

然后在其上运行.Take(1)。

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

你要使用Jon Skeet's库MiscUtil，而不是直接复制/粘贴代码。

Answer 2

或者你可以做两个线路（.NET 4只）

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

Answer 3

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; 
}