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.
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.
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;
}
