blocks|key|609531|text|使用correct+constructor|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|609532|else+if+(File.Exists(path))
{
++++using(var+tw+=+new+StreamWriter(path,+true))
++++{
++++++++tw.WriteLine("The+next+line!");
++++}
}|code-block|syntax|javascript|609533|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/36b035cb.aspx^0|2|J|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

Use the <a href="http://msdn.microsoft.com/en-us/library/36b035cb.aspx" rel="noreferrer">correct constructor</a>:

<pre><code>else if (File.Exists(path))
{
 using(var tw = new StreamWriter(path, true))
 {
 tw.WriteLine("The next line!");
 }
}
</code></pre>

blocks|key|609821|text|string+path=@"E:\AppServ\Example.txt";

if(!File.Exists(path))
{
+++File.Create(path).Dispose();

+++using(+TextWriter+tw+=+new+StreamWriter(path))
+++{
++++++tw.WriteLine("The+very+first+line!");
+++}

}++++
else+if+(File.Exists(path))
{
+++using(TextWriter+tw+=+new+StreamWriter(path))
+++{
++++++tw.WriteLine("The+next+line!");
+++}
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|609822|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>string path=@"E:\AppServ\Example.txt";

if(!File.Exists(path))
{
 File.Create(path).Dispose();

 using( TextWriter tw = new StreamWriter(path))
 {
 tw.WriteLine("The very first line!");
 }

} 
else if (File.Exists(path))
{
 using(TextWriter tw = new StreamWriter(path))
 {
 tw.WriteLine("The next line!");
 }
}
</code></pre>

blocks|key|393694|text|实际上，您不必检查该文件是否存在，因为StreamWriter将为您做这件事。如果你在append-mode中打开它，如果文件不存在，将会被创建，然后你将总是追加，并且永远不会覆盖。所以你的初始检查是多余的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|393695|TextWriter+tw+=+new+StreamWriter(path,+true);
tw.WriteLine("The+next+line!");
tw.Close();+|code-block|syntax|javascript|393696|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|$]]

You don't actually have to check if the file exists, as StreamWriter will do that for you. If you open it in append-mode, the file will be created if it does not exists, then you will always append and never over write. So your initial check is redundant.

<pre><code>TextWriter tw = new StreamWriter(path, true);
tw.WriteLine("The next line!");
tw.Close(); 
</code></pre>

blocks|key|610045|text|File.AppendAllText将字符串添加到文件中。如果文本文件不存在，它还会创建一个文本文件。如果你不需要阅读内容，这是非常有效的。用例是日志记录。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|610046|File.AppendAllText("C:\\log.txt",+"hello+world\n");|code-block|syntax|javascript|610047|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|$]]

File.AppendAllText adds a string to a file. It also creates a text file if the file does not exist. If you don't need to read content, it's very efficient. The use case is logging.

<pre><code>File.AppendAllText("C:\\log.txt", "hello world\n");
</code></pre>

blocks|key|609616|text|你只想在“追加”模式下打开文件。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|609617|http://msdn.microsoft.com/en-us/library/3zc0w663.aspx|offset|length|609618|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|1H|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@$D|O|E|P|1|Q]]|A|$]]|$1|F|3|-4|5|6|7|R|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|C]]]]

You just want to open the file in "append" mode. 

<a href="http://msdn.microsoft.com/en-us/library/3zc0w663.aspx">http://msdn.microsoft.com/en-us/library/3zc0w663.aspx</a>

blocks|key|393954|text|您可以只使用File.AppendAllText()方法，这将解决您的问题。此方法将负责创建文件，如果不可用，则打开和关闭文件。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|393955|var+outputPath+=+@"E:\Example.txt";
var+data+=+"Example+Data";
File.AppendAllText(outputPath,+data);|code-block|syntax|javascript|393956|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|$]]

You can just use File.AppendAllText() Method this will solve your problem.
This method will take care of File Creation if not available, opening and closing the file.

<pre><code>var outputPath = @"E:\Example.txt";
var data = "Example Data";
File.AppendAllText(outputPath, data);
</code></pre>

blocks|key|609796|text|当你启动StreamWriter时，它会覆盖之前存在的文本。您可以像这样使用append+property：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|609797|TextWriter+t+=+new+StreamWriter(path,+true);|code-block|syntax|javascript|609798|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|$]]

When you start StreamWriter it's override the text was there before. You can use append property like so:

<pre><code>TextWriter t = new StreamWriter(path, true);
</code></pre>

blocks|key|609807|text|+else+if+(File.Exists(path))+
{+
++using+(StreamWriter+w+=+File.AppendText(path))
++++++++{
++++++++++++w.WriteLine("The+next+line!");+
++++++++++++w.Close();
++++++++}
+}+|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|609808|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code> else if (File.Exists(path)) 
{ 
 using (StreamWriter w = File.AppendText(path))
 {
 w.WriteLine("The next line!"); 
 w.Close();
 }
 } 
</code></pre>

blocks|key|610069|text|尝尝这个。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|610070|string+path+=+@"E:\AppServ\Example.txt";
if+(!File.Exists(path))
{
++++using+(var+txtFile+=+File.AppendText(path))
++++{
++++++++txtFile.WriteLine("The+very+first+line!");
++++}
}
else+if+(File.Exists(path))
{+++++
++++using+(var+txtFile+=+File.AppendText(path))
++++{
++++++++txtFile.WriteLine("The+next+line!");
++++}
}|code-block|syntax|javascript|610071|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|$]]

Try this.

<pre><code>string path = @"E:\AppServ\Example.txt";
if (!File.Exists(path))
{
 using (var txtFile = File.AppendText(path))
 {
 txtFile.WriteLine("The very first line!");
 }
}
else if (File.Exists(path))
{ 
 using (var txtFile = File.AppendText(path))
 {
 txtFile.WriteLine("The next line!");
 }
}
</code></pre>

blocks|key|393545|text|你可以使用FileStream。这为你做了所有的工作。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|393546|http://www.csharp-examples.net/filestream-open-file/|offset|length|393547|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|1G|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@$D|O|E|P|1|Q]]|A|$]]|$1|F|3|-4|5|6|7|R|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|C]]]]

You could use a FileStream. This does all the work for you.

<a href="http://www.csharp-examples.net/filestream-open-file/" rel="nofollow">http://www.csharp-examples.net/filestream-open-file/</a>

blocks|key|609957|text|在微软文档中，如果文件不存在，您可以创建文件，并在单个调用File.AppendAllText方法(String、 String)中附加到该文件|type|unstyled|depth|inlineStyleRanges|entityRanges|data|609958|.NET框架(当前版本)其他版本|609959|打开一个文件，将指定的字符串追加到该文件，然后关闭该文件。如果文件不存在，此方法将创建一个文件，将指定的字符串写入该文件，然后关闭该文件。命名空间:+System.IO程序集:+mscorlib+(在mscorlib.dll中)|609960|语法C#C%2B%2BF#VB公共静态空AppendAllText(+string+path，string+contents+)参数path类型:+System.String要追加指定字符串的文件。内容类型:+System.String要附加到文件的字符串。|609961|AppendAllText|offset|length|609962|entityMap|0|LINK|mutability|MUTABLE|url|https://msdn.microsoft.com/en-us/library/microsoft.synchronization.syncdirectionorder(v=sql.105).aspx?cs-save-lang=1&cs-lang=csharp#code-snippet-1^0|0|0|0|0|0|D|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|U|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|V|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|W|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|X|8|@]|9|@$J|Y|K|Z|1|10]]|A|$]]|$1|L|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|M|$N|$5|O|P|Q|A|$R|S]]]]

From microsoft documentation, you can create file if not exist and append to it in a single call
File.AppendAllText Method (String, String)

.NET Framework (current version) Other Versions 

Opens a file, appends the specified string to the file, and then closes the file. If the file does not exist, this method creates a file, writes the specified string to the file, then closes the file.
Namespace: System.IO
Assembly: mscorlib (in mscorlib.dll)

Syntax
C#C++F#VB
public static void AppendAllText(
 string path,
 string contents
)
Parameters
path
Type: System.String
The file to append the specified string to.
contents
Type: System.String
The string to append to the file.

<a href="https://msdn.microsoft.com/en-us/library/microsoft.synchronization.syncdirectionorder(v=sql.105).aspx?cs-save-lang=1&amp;cs-lang=csharp#code-snippet-1" rel="nofollow">AppendAllText</a>

blocks|key|610057|text|using(var+tw+=+new+StreamWriter(path,+File.Exists(path)))
{
++++tw.WriteLine(message);
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|610058|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>using(var tw = new StreamWriter(path, File.Exists(path)))
{
 tw.WriteLine(message);
}
</code></pre>

blocks|key|610177|text|.NET核心控制台应用程序：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|610178|public+static+string+RootDir()+=>+Path.GetFullPath(Path.Combine(AppContext.BaseDirectory,+@"..\..\..\"));


string+_OutputPath+=+RootDir()+%2B+"\\Output\\"+%2B+"MyFile.txt";
if+(!File.Exists(_OutputPath))
++++File.Create(_OutputPath).Dispose();
using+(TextWriter+_StreamWriter+=+new+StreamWriter(_OutputPath))
{
++++_StreamWriter.WriteLine(strOriginalText);
}|code-block|syntax|javascript|610179|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|$]]

.NET Core Console App:
<pre><code>public static string RootDir() =&gt; Path.GetFullPath(Path.Combine(AppContext.BaseDirectory, @&quot;..\..\..\&quot;));


string _OutputPath = RootDir() + &quot;\\Output\\&quot; + &quot;MyFile.txt&quot;;
if (!File.Exists(_OutputPath))
 File.Create(_OutputPath).Dispose();
using (TextWriter _StreamWriter = new StreamWriter(_OutputPath))
{
 _StreamWriter.WriteLine(strOriginalText);
}


 
</code></pre>

blocks|key|394064|text|请注意，AppendAllLines和AppendAllText方法只创建文件，而不创建路径。因此，如果您尝试在"C:\Folder“中创建文件，请确保此路径存在。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|394065|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|$]]

Please note that AppendAllLines and AppendAllText methods only create the file, but not the path. So if you are trying to create a file in &quot;C:\Folder&quot;, please ensure that this path exists.

I would like to create a .txt file and write to it, and if the file already exists I just want to append some more lines:

<pre><code>string path = @"E:\AppServ\Example.txt";
if (!File.Exists(path))
{
 File.Create(path);
 TextWriter tw = new StreamWriter(path);
 tw.WriteLine("The very first line!");
 tw.Close();
}
else if (File.Exists(path))
{
 TextWriter tw = new StreamWriter(path);
 tw.WriteLine("The next line!");
 tw.Close(); 
}
</code></pre>

But the first line seems to always get overwritten... how can I avoid writing on the same line (I'm using this in a loop)?

I know it's a pretty simple thing, but I never used the <code>WriteLine</code> method before. I'm totally new to C#.

Create a .txt file if doesn't exist, and if it does append a new line

我想创建一个.txt文件并写入它，如果该文件已经存在，我只想追加一些行：string path = @"E:\AppServ\Example.txt";if (!File.Exists(path)){    File.Create(path);    TextWriter tw = new StreamWriter(path);    tw.WriteLine("The very first li

问如果不存在，则创建一个.txt文件，如果存在，则附加一个新行
EN

回答 14

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问如果不存在，则创建一个.txt文件，如果存在，则附加一个新行EN

回答 14

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问如果不存在，则创建一个.txt文件，如果存在，则附加一个新行
EN