［Utility］自製吃一次檔案尾巴的小工具 Tail()
找了一下G大神, 似乎沒有馬上可套用的, 自己就寫一寫囉^^
真相細節就在程式的註解中, 請慢慢服用
1: /// <summary>
2: /// 吃一次檔案尾巴的小工具. (example: log file)
3: /// </summary>
4: /// @Author Hector Lee
5: /// @Since 2011/12/30
6: /// <param name="path">完整的檔案路徑</param>
7: /// <param name="lines">要吃幾行尾巴</param>
8: /// <param name="encoding">文字的編碼方式</param>
9: /// <returns>依編碼方式讀入的檔案尾巴文字</returns>
10: public static string Tail(string path, int lines, Encoding encoding)
11: {
12: string result = "";
13: // 暫存器
14: using (MemoryStream output = new MemoryStream())
15: {
16: // 讀取器
17: using (BufferedStream stream = new BufferedStream(new FileStream(path, FileMode.Open, FileAccess.Read)))
18: {
19: // move to before end
20: stream.Seek(-1, SeekOrigin.End);
21: // read a byte
22: int b = stream.ReadByte();
23:
24: // 當達到最大行數時或讀到檔頭(b=-1)時
25: for (int stack = lines; stack >= 0 && b > 0; )
26: {
27: // 寫入暫存器
28: output.WriteByte((byte)b);
29:
30: try
31: {
32: // 往前移2位, 然後讀1位.
33: stream.Seek(-2, SeekOrigin.Current);
34: b = stream.ReadByte();
35: }
36: catch (IOException)
37: {
38: // 如果讀到檔頭, 就要離開迴圈了
39: b = -1;
40: }
41:
42: if (b == 10) // \n ascii code is 10 (lf) 13(cr)
43: {
44: // 如果讀到change line時,將尾巴就要少一條.
45: stack--;
46: }
47:
48: }
49: // 暫存器吐出到陣列, 然後倒序回來(因為是從尾巴讀起)
50: byte[] bytes = output.ToArray();
51: Array.Reverse(bytes);
52: // 依編碼方式轉成字串
53: result = encoding.GetString(bytes);
54: }
55: }
56:
57: return result;
58: }