C# · 12月 29, 2021

c# – 如何读取最后一个“n”行的日志文件

需要一段代码,可以读出日志文件的最后一行“n行”.我从网上提出了以下代码.我对C sharp有点新鲜.由于日志文件可能是
相当大,我想避免阅读整个文件的开销.有人建议任何性能提升.我真的不想读每个字符并改变位置. var reader = new StreamReader(filePath,Encoding.ASCII); reader.BaseStream.Seek(0,SeekOrigin.End); var count = 0; while (count <= tailCount) { if (reader.BaseStream.Position <= 0) break; reader.BaseStream.Position–; int c = reader.Read(); if (reader.BaseStream.Position <= 0) break; reader.BaseStream.Position–; if (c == ‘\n’) { ++count; } } var str = reader.ReadToEnd();解决方法 您的代码将执行得很差,因为您不允许任何缓存发生.
另外,对于Unicode来说,它根本不起作用.

我写了以下实现:

///<summary>Returns the end of a text reader.</summary>///<param name=”reader”>The reader to read from.</param>///<param name=”lineCount”>The number of lines to return.</param>///<returns>The last lneCount lines from the reader.</returns>public static string[] Tail(this TextReader reader,int lineCount) { var buffer = new List<string>(lineCount); string line; for (int i = 0; i < lineCount; i++) { line = reader.ReadLine(); if (line == null) return buffer.ToArray(); buffer.Add(line); } int lastLine = lineCount – 1; //The index of the last line read from the buffer. Everything > this index was read earlier than everything <= this indes while (null != (line = reader.ReadLine())) { lastLine++; if (lastLine == lineCount) lastLine = 0; buffer[lastLine] = line; } if (lastLine == lineCount – 1) return buffer.ToArray(); var retVal = new string[lineCount]; buffer.CopyTo(lastLine + 1,retVal,lineCount – lastLine – 1); buffer.CopyTo(0,lineCount – lastLine – 1,lastLine + 1); return retVal;}