blocks|key|556332|text|如果创建一个新的IO.FileStream()对象，就会有一个.Seek()方法，它允许您将文件的结尾指定为要查找的位置的一部分。然而，在这一点上，没有直接的方法来查看最后一行从哪里开始。你将不得不向后走寻找一条线，或者如果你知道最后一条线是什么样子(因此它有多长)，你也许能够猜测你需要往回走多远，然后再走一点。使用FileStream.CanSeek属性确定当前实例是否支持查找。有关其他信息，请参阅Stream.CanSeek。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|556333|FileStream++fileStream+=+new+FileStream(fileName,+FileMode.Open)
//+Set+the+stream+position+to+the+end+of+the+file.
fileStream.Seek(0,+SeekOrigin.End);|code-block|syntax|javascript|556334|然后循环一遍，直到得到/n|556335|你也可以读到另一个问题：How+to+read+a+text+file+reversely+with+iterator+in+C#|556336|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/452902/how-to-read-a-text-file-reversely-with-iterator-in-c-sharp^0|V|7|4F|I|0|0|0|C|1H|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|11|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|12|8|@]|D|@]|E|$]]|$1|M|3|N|5|6|7|13|8|@]|D|@$9|14|A|15|1|16]]|E|$]]|$1|O|3|-4|5|6|7|17|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]]]

If you create a new IO.FileStream() object, there's a .Seek() method that will allow you specify the end of the file as part of where you want to seek to. However, at this point there's no straightforward way to see where the last line starts. You'll have to either walk backwards looking for a line, or if you have an idea of what this last line looks like (and therefore how long it is) you might be able to make a guess as to how far back you need to seek and go just a little further.
Use the FileStream.CanSeek property to determine whether the current instance supports seeking. For additional information, see Stream.CanSeek.

<pre><code>FileStream fileStream = new FileStream(fileName, FileMode.Open)
// Set the stream position to the end of the file.
fileStream.Seek(0, SeekOrigin.End);
</code></pre>

then go over in loop until you get your /n

you can also read in this other question: <a href="https://stackoverflow.com/questions/452902/how-to-read-a-text-file-reversely-with-iterator-in-c-sharp">How to read a text file reversely with iterator in C#</a>

blocks|key|4687066|text|从我的脑海中|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4687067|string+lastline+=+input.Substring(
+++input.LastIndexOf('\n'));|code-block|syntax|javascript|4687068|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

from the top of my head 

<pre><code>string lastline = input.Substring(
 input.LastIndexOf('\n'));
</code></pre>

blocks|key|1573005|text|如果您在读取任何文件时需要更好的性能，您可以使用内存映射文件读/写，即在低级API上工作。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1573006|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

If you need better performance when reading any file, You can go for memory map file reading/writing, that is to work at the low level APIs.

blocks|key|1573012|text|(注意:它不是C#，而是VB.NET)我不久前翻译了a+function+that+I+created+for+Python。不确定只搜索\n是最好的选择...|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1573013|Public+Function+tail(ByVal+filepath+As+String)+As+String
++++'+@author+marco+sulla+(marcosullaroma@gmail.com)
++++'+@date+may+31,+2016

++++Dim+fp+As+String+=+filepath
++++Dim+res+As+String

++++Using+f+As+FileStream+=+File.Open(fp,+FileMode.Open,+FileAccess.Read)
++++++++Dim+f_info+As+New+FileInfo(fp)
++++++++Dim+size+As+Long+=+f_info.Length
++++++++Dim+start_pos+As+Long+=+size+-+1

++++++++If+start_pos+<+0+Then
++++++++++++start_pos+=+0
++++++++End+If

++++++++If+start_pos+<>+0+Then
++++++++++++f.Seek(start_pos,+SeekOrigin.Begin)
++++++++++++Dim+mychar+As+Integer+=+f.ReadByte()

++++++++++++If+mychar+=+10+Then++'+newline
++++++++++++++++start_pos+-=+1
++++++++++++++++f.Seek(start_pos,+SeekOrigin.Begin)
++++++++++++End+If

++++++++++++If+start_pos+=+0+Then
++++++++++++++++f.Seek(start_pos,+SeekOrigin.Begin)
++++++++++++Else
++++++++++++++++mychar+=+-1

++++++++++++++++For+pos+As+Long+=+start_pos+To+0+Step+-1
++++++++++++++++++++f.Seek(pos,+SeekOrigin.Begin)

++++++++++++++++++++mychar+=+f.ReadByte()

++++++++++++++++++++If+mychar+=+10+Then
++++++++++++++++++++++++Exit+For
++++++++++++++++++++End+If
++++++++++++++++Next
++++++++++++End+If
++++++++End+If

++++++++Using+r+As+StreamReader+=+New+StreamReader(f,+Encoding.UTF8)
++++++++++++res+=+r.ReadLine()
++++++++End+Using
++++End+Using

++++Return+res
End+Function|code-block|syntax|javascript|1573014|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/37551666/1763602^0|1X|2|Q|10|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@$9|V|A|W|1|X]]|E|$]]|$1|F|3|G|5|H|7|Y|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|L|$M|$5|N|O|P|E|$Q|R]]]]

(Note: It's not C# but VB.NET) I translated <a href="https://stackoverflow.com/a/37551666/1763602">a function that I created for Python</a> a few time ago. Not sure that searching for <code>\n</code> only is the best choice...

<pre><code>Public Function tail(ByVal filepath As String) As String
 ' @author marco sulla (marcosullaroma@gmail.com)
 ' @date may 31, 2016

 Dim fp As String = filepath
 Dim res As String

 Using f As FileStream = File.Open(fp, FileMode.Open, FileAccess.Read)
 Dim f_info As New FileInfo(fp)
 Dim size As Long = f_info.Length
 Dim start_pos As Long = size - 1

 If start_pos &lt; 0 Then
 start_pos = 0
 End If

 If start_pos &lt;&gt; 0 Then
 f.Seek(start_pos, SeekOrigin.Begin)
 Dim mychar As Integer = f.ReadByte()

 If mychar = 10 Then ' newline
 start_pos -= 1
 f.Seek(start_pos, SeekOrigin.Begin)
 End If

 If start_pos = 0 Then
 f.Seek(start_pos, SeekOrigin.Begin)
 Else
 mychar = -1

 For pos As Long = start_pos To 0 Step -1
 f.Seek(pos, SeekOrigin.Begin)

 mychar = f.ReadByte()

 If mychar = 10 Then
 Exit For
 End If
 Next
 End If
 End If

 Using r As StreamReader = New StreamReader(f, Encoding.UTF8)
 res = r.ReadLine()
 End Using
 End Using

 Return res
End Function
</code></pre>

any idea how to read last or two last lines of a file containing about 30 lines with <code>\n</code> with focus on performance speed?

EDIT:
something faster than: 

<pre><code>string[] splitedArray= input.Split('\n');
string lastLine = splitedArray[splitedArray.Length-1];
</code></pre>

Using c#

A performant way to read the last line of a file in C#

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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你知道如何使用\n读取包含大约30行的文件的最后一行或最后两行，并关注性能速度吗？编辑:比以下内容更快的东西：string[] splitedArray= input.Split('\n');string lastLine = splitedArray[splitedArray.Length-1];使用c#

问在C#中读取文件最后一行的一种高效方法
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