使用FileStream.Seek [英] Using FileStream.Seek
本文介绍了使用FileStream.Seek的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我试图用FileStream.Seek合作快速跳转到一条线，读它。
I am trying to work with FileStream.Seek to quickly jump to a line and read it.
不过，我没有得到正确的结果。我曾尝试看看这一段时间，无法理解我在做什么错
However, I am not getting the right results. I have tried to look at this for a while and can't understand what I am doing wrong.
环境：结果
操作系统：Windows 7 < BR>
框架：.NET 4.0结果
IDE：的Visual C＃快讯2010
Environment:
OS: Windows 7
Framework: .NET 4.0
IDE: Visual C# Express 2010
<文件位置STRONG>样本数据：C： \Temp\Temp.txt
0001|100!2500
0002|100!2500
0003|100!2500
0004|100!2500
0005|100!2500
0006|100!2500
0007|100!2500
0008|100!2500
0009|100!2500
0010|100!2500
代码：！
class PaddedFileSearch
{
private int LineLength { get; set; }
private string FileName { get; set; }
public PaddedFileSearch()
{
FileName = @"C:\Temp\Temp.txt"; // This is a padded file. All lines are of the same length.
FindLineLength();
Debug.Print("File Line length: {0}", LineLength);
// TODO: This purely for testing. Move this code out.
SeekMethod(new int[] { 5, 3, 4 });
/* Expected Results:
* Line No Position Line
* ------- -------- -----------------
* 3 30 0003|100!2500
* 4 15 0004|100!2500
* 5 15 0005|100!2500 -- This was updated after the initial request.
*/
/* THIS DOES NOT GIVE THE EXPECTED RESULTS */
SeekMethod(new int[] { 5, 3 });
/* Expected Results:
* Line No Position Line
* ------- -------- -----------------
* 3 30 0003|100!2500
* 5 30 0005|100!2500
*/
}
private void FindLineLength()
{
string line;
// Add check for FileExists
using (StreamReader reader = new StreamReader(FileName))
{
if ((line = reader.ReadLine()) != null)
{
LineLength = line.Length + 2;
// The 2 is for NewLine(\r\n)
}
}
}
public void SeekMethod(int[] lineNos)
{
long position = 0;
string line = null;
Array.Sort(lineNos);
Debug.Print("");
Debug.Print("Line No\t\tPosition\t\tLine");
Debug.Print("-------\t\t--------\t\t-----------------");
using (FileStream fs = new FileStream(FileName, FileMode.Open, FileAccess.Read, FileShare.None))
{
using (StreamReader reader = new StreamReader(fs))
{
foreach (int lineNo in lineNos)
{
position = (lineNo - 1) * LineLength - position;
fs.Seek(position, SeekOrigin.Current);
if ((line = reader.ReadLine()) != null)
{
Debug.Print("{0}\t\t\t{1}\t\t\t\t{2}", lineNo, position, line);
}
}
}
}
}
}
输出我得到：
File Line length: 15
Line No Position Line
------- -------- -----------------
3 30 0003|100!2500
4 15 0004|100!2500
5 45 0005|100!2500
Line No Position Line
------- -------- -----------------
3 30 0003|100!2500
5 30 0004|100!2500
我的问题是与下面的输出：
Line No Position Line
------- -------- -----------------
5 30 0004|100!2500
有关线路的输出应该是：！ 0005 | 100 2500
The output for Line should be: 0005|100!2500
我不明白为什么会这样。
I don't understand why this is happening.
我是不是做错了什么？
是否有解决方法吗？
也有没有更快的方式做到这一点使用像求？结果
（我找了基于代码的选项和的不的 Oracle或SQL Server中。对于参数的缘故让也说，文件大小为1 GB）。
Am I doing something wrong?
Is there a workaround?
Also are there faster ways to do this using something like seek?
(I am looking for code based options and NOT Oracle or SQL Server. For the sake of argument lets also say that the file size 1 GB.)
任何帮助是极大的赞赏。
Any help is greatly appreciated.
感谢。
更新：结果
我发现这里4伟大的答案。 。非常感谢
UPDATE:
I found 4 great answers here. Thanks a lot.
采样定时：结果
根据几运行，以下是从最好到好方法。连好非常接近最好的。结果，
在包含10K行，2.28 MB的一个文件。我搜索了使用的所有选项相同的5000随机行
Sample Timings:
Based on a few runs the following are the methods from best to good. Even the good is very close to best.
In a file that contains 10K lines, 2.28 MB. I searched for same 5000 random lines using all the options.
- Seek4：经过时间：00：00：00.0398530毫秒 - Ritch梅尔顿
- Seek3：经过时间：00：00：00.0446072毫秒 - 瓦伦丁Kuzub
- Seek1：经过时间：00：00：00.0538210毫秒 - 杰克
- Seek2：经过时间：00：00：00.0889589毫秒 - bitxwise
- Seek4: Time elapsed: 00:00:00.0398530 ms -- Ritch Melton
- Seek3: Time elapsed: 00:00:00.0446072 ms -- Valentin Kuzub
- Seek1: Time elapsed: 00:00:00.0538210 ms -- Jake
- Seek2: Time elapsed: 00:00:00.0889589 ms -- bitxwise
下面显示的是代码。保存代码后，你可以简单地键入称之为 TestPaddedFileSeek.CallPaddedFileSeek（）; 。您还可以指定命名空间和使用引用。
Shown below is the code. After saving the code you can simply call it by typing TestPaddedFileSeek.CallPaddedFileSeek();. You will also have to specify the namespace and the "using references".
`
/// <summary>
/// This class multiple options of reading a by line number in a padded file (all lines are the same length).
/// The idea is to quick jump to the file.
/// Details about the discussions is available at: http://stackoverflow.com/questions/5201414/having-a-problem-while-using-filestream-seek-in-c-solved
/// </summary>
class PaddedFileSeek
{
public FileInfo File {get; private set;}
public int LineLength { get; private set; }
#region Private methods
private static int FindLineLength(FileInfo fileInfo)
{
using (StreamReader reader = new StreamReader(fileInfo.FullName))
{
string line;
if ((line = reader.ReadLine()) != null)
{
int length = line.Length + 2; // The 2 is for NewLine(\r\n)
return length;
}
}
return 0;
}
private static void PrintHeader()
{
/*
Debug.Print("");
Debug.Print("Line No\t\tLine");
Debug.Print("-------\t\t--------------------------");
*/
}
private static void PrintLine(int lineNo, string line)
{
//Debug.Print("{0}\t\t\t{1}", lineNo, line);
}
private static void PrintElapsedTime(TimeSpan elapsed)
{
Debug.WriteLine("Time elapsed: {0} ms", elapsed);
}
#endregion
public PaddedFileSeek(FileInfo fileInfo)
{
// Possibly might have to check for FileExists
int length = FindLineLength(fileInfo);
//if (length == 0) throw new PaddedProgramException();
LineLength = length;
File = fileInfo;
}
public void CallAll(int[] lineNoArray, List<int> lineNoList)
{
Stopwatch sw = new Stopwatch();
#region Seek1
// Create new stopwatch
sw.Start();
Debug.Write("Seek1: ");
// Print Header
PrintHeader();
Seek1(lineNoArray);
// Stop timing
sw.Stop();
// Print Elapsed Time
PrintElapsedTime(sw.Elapsed);
sw.Reset();
#endregion
#region Seek2
// Create new stopwatch
sw.Start();
Debug.Write("Seek2: ");
// Print Header
PrintHeader();
Seek2(lineNoArray);
// Stop timing
sw.Stop();
// Print Elapsed Time
PrintElapsedTime(sw.Elapsed);
sw.Reset();
#endregion
#region Seek3
// Create new stopwatch
sw.Start();
Debug.Write("Seek3: ");
// Print Header
PrintHeader();
Seek3(lineNoArray);
// Stop timing
sw.Stop();
// Print Elapsed Time
PrintElapsedTime(sw.Elapsed);
sw.Reset();
#endregion
#region Seek4
// Create new stopwatch
sw.Start();
Debug.Write("Seek4: ");
// Print Header
PrintHeader();
Seek4(lineNoList);
// Stop timing
sw.Stop();
// Print Elapsed Time
PrintElapsedTime(sw.Elapsed);
sw.Reset();
#endregion
}
/// <summary>
/// Option by Jake
/// </summary>
/// <param name="lineNoArray"></param>
public void Seek1(int[] lineNoArray)
{
long position = 0;
string line = null;
Array.Sort(lineNoArray);
using (FileStream fs = new FileStream(File.FullName, FileMode.Open, FileAccess.Read, FileShare.None))
{
using (StreamReader reader = new StreamReader(fs))
{
foreach (int lineNo in lineNoArray)
{
position = (lineNo - 1) * LineLength;
fs.Seek(position, SeekOrigin.Begin);
if ((line = reader.ReadLine()) != null)
{
PrintLine(lineNo, line);
}
reader.DiscardBufferedData();
}
}
}
}
/// <summary>
/// option by bitxwise
/// </summary>
public void Seek2(int[] lineNoArray)
{
string line = null;
long step = 0;
Array.Sort(lineNoArray);
using (FileStream fs = new FileStream(File.FullName, FileMode.Open, FileAccess.Read, FileShare.None))
{
// using (StreamReader reader = new StreamReader(fs))
// If you put "using" here you will get WRONG results.
// I would like to understand why this is.
{
foreach (int lineNo in lineNoArray)
{
StreamReader reader = new StreamReader(fs);
step = (lineNo - 1) * LineLength - fs.Position;
fs.Position += step;
if ((line = reader.ReadLine()) != null)
{
PrintLine(lineNo, line);
}
}
}
}
}
/// <summary>
/// Option by Valentin Kuzub
/// </summary>
/// <param name="lineNoArray"></param>
#region Seek3
public void Seek3(int[] lineNoArray)
{
long position = 0; // totalPosition = 0;
string line = null;
int oldLineNo = 0;
Array.Sort(lineNoArray);
using (FileStream fs = new FileStream(File.FullName, FileMode.Open, FileAccess.Read, FileShare.None))
{
using (StreamReader reader = new StreamReader(fs))
{
foreach (int lineNo in lineNoArray)
{
position = (lineNo - oldLineNo - 1) * LineLength;
fs.Seek(position, SeekOrigin.Current);
line = ReadLine(fs, LineLength);
PrintLine(lineNo, line);
oldLineNo = lineNo;
}
}
}
}
#region Required Private methods
/// <summary>
/// Currently only used by Seek3
/// </summary>
/// <param name="stream"></param>
/// <param name="length"></param>
/// <returns></returns>
private static string ReadLine(FileStream stream, int length)
{
byte[] bytes = new byte[length];
stream.Read(bytes, 0, length);
return new string(Encoding.UTF8.GetChars(bytes));
}
#endregion
#endregion
/// <summary>
/// Option by Ritch Melton
/// </summary>
/// <param name="lineNoArray"></param>
#region Seek4
public void Seek4(List<int> lineNoList)
{
lineNoList.Sort();
using (var fs = new FileStream(File.FullName, FileMode.Open))
{
lineNoList.ForEach(ln => OutputData(fs, ln));
}
}
#region Required Private methods
private void OutputData(FileStream fs, int lineNumber)
{
var offset = (lineNumber - 1) * LineLength;
fs.Seek(offset, SeekOrigin.Begin);
var data = new byte[LineLength];
fs.Read(data, 0, LineLength);
var text = DecodeData(data);
PrintLine(lineNumber, text);
}
private static string DecodeData(byte[] data)
{
var encoding = new UTF8Encoding();
return encoding.GetString(data);
}
#endregion
#endregion
}
static class TestPaddedFileSeek
{
public static void CallPaddedFileSeek()
{
const int arrayLenght = 5000;
int[] lineNoArray = new int[arrayLenght];
List<int> lineNoList = new List<int>();
Random random = new Random();
int lineNo;
string fileName;
fileName = @"C:\Temp\Temp.txt";
PaddedFileSeek seeker = new PaddedFileSeek(new FileInfo(fileName));
for (int n = 0; n < 25; n++)
{
Debug.Print("Loop no: {0}", n + 1);
for (int i = 0; i < arrayLenght; i++)
{
lineNo = random.Next(1, arrayLenght);
lineNoArray[i] = lineNo;
lineNoList.Add(lineNo);
}
seeker.CallAll(lineNoArray, lineNoList);
lineNoList.Clear();
Debug.Print("");
}
}
}
`
`
推荐答案
我被你的预期位置，5号线在位置30和45在15混为一谈，与4号线和3在30？
I'm confused by your expected positions, Line 5 at position 30 and 45, with Line 4 at 15, and 3 at 30?
下面是读逻辑的核心是：
Here's the core of the read logic:
var offset = (lineNumber - 1) * LineLength;
fs.Seek(offset, SeekOrigin.Begin);
var data = new byte[LineLength];
fs.Read(data, 0, LineLength);
var text = DecodeData(data);
Debug.Print("{0,-12}{1,-16}{2}", lineNumber, offset, text);
完整的样本是在这里：
The full sample is here:
class PaddedFileSearch
{
public int LineLength { get; private set; }
public FileInfo File { get; private set; }
public PaddedFileSearch(FileInfo fileInfo)
{
var length = FindLineLength(fileInfo);
//if (length == 0) throw new PaddedProgramException();
LineLength = length;
File = fileInfo;
}
private static int FindLineLength(FileInfo fileInfo)
{
using (var reader = new StreamReader(fileInfo.FullName))
{
string line;
if ((line = reader.ReadLine()) != null)
{
var length = line.Length + 2;
return length;
}
}
return 0;
}
public void SeekMethod(List<int> lineNumbers)
{
Debug.Print("");
Debug.Print("Line No\t\tPosition\t\tLine");
Debug.Print("-------\t\t--------\t\t-----------------");
lineNumbers.Sort();
using (var fs = new FileStream(File.FullName, FileMode.Open))
{
lineNumbers.ForEach(ln => OutputData(fs, ln));
}
}
private void OutputData(FileStream fs, int lineNumber)
{
var offset = (lineNumber - 1) * LineLength;
fs.Seek(offset, SeekOrigin.Begin);
var data = new byte[LineLength];
fs.Read(data, 0, LineLength);
var text = DecodeData(data);
Debug.Print("{0,-12}{1,-16}{2}", lineNumber, offset, text);
}
private static string DecodeData(byte[] data)
{
var encoding = new UTF8Encoding();
return encoding.GetString(data);
}
}
class Program
{
static void Main(string[] args)
{
var seeker = new PaddedFileSearch(new FileInfo(@"D:\Desktop\Test.txt"));
Debug.Print("File Line length: {0}", seeker.LineLength);
seeker.SeekMethod(new List<int> { 5, 3, 4 });
seeker.SeekMethod(new List<int> { 5, 3 });
}
}
这篇关于使用FileStream.Seek的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
查看全文
