blocks|key|946568|text|public+static+string+TruncateLongString(this+string+str,+int+maxLength)
{
++++if+(string.IsNullOrEmpty(str))+return+str;

++++return+str.Substring(0,+Math.Min(str.Length,+maxLength));
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|946569|在C#+8或更高版本中，也可以使用Range使其更简洁：|unstyled|offset|length|946570|public+static+string+TruncateLongString(this+string+str,+int+maxLength)
{
++++return+str?[0..Math.Min(str.Length,+maxLength)];
}|946571|可以使用表达式体进一步减少：|946572|public+static+string+TruncateLongString(this+string+str,+int+maxLength)+=>
++++str?[0..Math.Min(str.Length,+maxLength)];|946573|注null+-条件运算符(?)用于处理str为null的情况。这取代了显式null检查的需要。|style|CODE|946574|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-8.0/ranges^0|0|H|5|0|0|0|0|0|D|1|J|3|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|11|8|@]|9|@$G|12|H|13|1|14]]|A|$]]|$1|I|3|J|5|6|7|15|8|@]|9|@]|A|$B|C]]|$1|K|3|L|5|F|7|16|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|17|8|@]|9|@]|A|$B|C]]|$1|O|3|P|5|F|7|18|8|@$G|19|H|1A|Q|R]|$G|1B|H|1C|Q|R]]|9|@]|A|$]]|$1|S|3|-4|5|F|7|1D|8|@]|9|@]|A|$]]]|T|$U|$5|V|W|X|A|$Y|Z]]]]

<pre><code>public static string TruncateLongString(this string str, int maxLength)
{
 if (string.IsNullOrEmpty(str)) return str;

 return str.Substring(0, Math.Min(str.Length, maxLength));
}
</code></pre>
In C# 8 or later it is also possible to use a <a href="https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-8.0/ranges" rel="noreferrer">Range</a> to make this a bit terser:
<pre><code>public static string TruncateLongString(this string str, int maxLength)
{
 return str?[0..Math.Min(str.Length, maxLength)];
}
</code></pre>
Which can be further reduced using an expression body:
<pre><code>public static string TruncateLongString(this string str, int maxLength) =&gt;
 str?[0..Math.Min(str.Length, maxLength)];
</code></pre>
Note null-conditional operator (<code>?</code>) is there to handle the case where <code>str</code> is null. This replaces the need for an explict null check.

blocks|key|1160646|text|string+truncatedToNLength+=+new+string(s.Take(n).ToArray());++|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1160647|这个解决方案有一个很小的好处，就是如果n大于s.Length，它仍然会做正确的事情。|unstyled|1160648|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code>string truncatedToNLength = new string(s.Take(n).ToArray()); 
</code></pre>

This solution has a tiny bonus in that if n is greater than s.Length, it still does the right thing.

blocks|key|946624|text|您可以使用LINQ+str.Take(n)或str.SubString(0,+n)，后者将为n+>+str.Length抛出ArgumentOutOfRangeException异常。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|946625|请注意，LINQ版本返回一个IEnumerable<char>，因此您必须将IEnumerable<char>转换为string：new+string(s.Take(n).ToArray())。|946626|entityMap^0|A|B|M|J|1A|E|1Q|R|0|E|H|12|H|1M|6|1T|V|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]|$9|Q|A|R|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|I|$]]

You can use LINQ <code>str.Take(n)</code> or <code>str.SubString(0, n)</code>, where the latter will throw an <code>ArgumentOutOfRangeException</code> exception for <code>n &gt; str.Length</code>.

Mind that the LINQ version returns a <code>IEnumerable&lt;char&gt;</code>, so you'd have to convert the <code>IEnumerable&lt;char&gt;</code> to <code>string</code>: <code>new string(s.Take(n).ToArray())</code>.

blocks|key|1160703|text|简单地说：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1160704|public+static+String+Truncate(String+input,int+maxLength)
{
+++if(input.Length+>+maxLength)
++++++return+input.Substring(0,maxLength);
+++return+input;
}|code-block|syntax|javascript|1160705|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|$]]

Simply:

<pre><code>public static String Truncate(String input,int maxLength)
{
 if(input.Length &gt; maxLength)
 return input.Substring(0,maxLength);
 return input;
}
</code></pre>

blocks|key|1160669|text|public+static+string+TruncateLongString(this+string+str,+int+maxLength)
{
++++return+str.Length+<=+maxLength+?+str+:+str.Remove(maxLength);
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1160670|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>public static string TruncateLongString(this string str, int maxLength)
{
 return str.Length &lt;= maxLength ? str : str.Remove(maxLength);
}
</code></pre>

blocks|key|1160780|text|如果我们正在讨论验证，那么为什么我们没有检查空字符串条目。有什么特别的原因吗？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1160781|我认为下面的方法会有所帮助，因为IsNullOrEmpty是一个系统定义的方法，三元运算符的圈复杂度为1，而if()+{}+else+{}的值为2。|1160782|++++public+static+string+Truncate(string+input,+int+truncLength)
++++{
++++++++return+(!String.IsNullOrEmpty(input)+&&+input.Length+>=+truncLength)
+++++++++++++++++++?+input.Substring(0,+truncLength)
+++++++++++++++++++:+input;
++++}|code-block|syntax|javascript|1160783|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

if we are talking about validations also why we have not checked for null string entries. Any specific reasons?

I think below way help since IsNullOrEmpty is a system defined method and ternary operators have cyclomatic complexity = 1 while if() {} else {} has value 2.

<pre><code> public static string Truncate(string input, int truncLength)
 {
 return (!String.IsNullOrEmpty(input) &amp;&amp; input.Length &gt;= truncLength)
 ? input.Substring(0, truncLength)
 : input;
 }
</code></pre>

blocks|key|1160925|text|我在我的项目中添加了这个，只是因为我使用它的地方有很高的机会在循环中使用它，在一个在线托管的项目中，因此如果我可以管理它，我不想发生任何崩溃。这个长度适合我的专栏。我是C#7|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1160926|只有一句话：|1160927|+public+static+string+SubStringN(this+string+Message,+int+Len+=+499)+=>+!String.IsNullOrEmpty(Message)+?+(Message.Length+>=+Len+?+Message.Substring(0,+Len)+:+Message)+:+"";|code-block|syntax|javascript|1160928|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I added this in my project just because where I'm using it is a high chance of it being used in loops, in a project hosted online hence I didn't want any crashes if I could manage it. The length fits a column I have. It's C#7

Just a one line:

<pre><code> public static string SubStringN(this string Message, int Len = 499) =&gt; !String.IsNullOrEmpty(Message) ? (Message.Length &gt;= Len ? Message.Substring(0, Len) : Message) : "";
</code></pre>

blocks|key|947040|text|.NET子串方法充满了危险。我开发了处理各种场景的扩展方法。好的是它保留了原来的行为，但是当你添加一个额外的"true“参数时，它会求助于扩展方法来处理异常，并根据索引和长度返回最具逻辑性的值。例如，如果长度为负，则向后计数。您可以在以下位置查看测试结果：https://dotnetfiddle.net/m1mSH9上的各种值。这将使您清楚地了解它是如何解析子字符串的。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|947041|我总是将这些方法添加到我的所有项目中，并且从不担心代码崩溃，因为有些东西发生了变化，索引是无效的。下面是代码。|947042|++++public+static+String+Substring(this+String+val,+int+startIndex,+bool+handleIndexException)
++++{
++++++++if+(!handleIndexException)
++++++++{+//handleIndexException+is+false+so+call+the+base+method
++++++++++++return+val.Substring(startIndex);
++++++++}
++++++++if+(string.IsNullOrEmpty(val))
++++++++{
++++++++++++return+val;
++++++++}
++++++++return+val.Substring(startIndex+<+0+?+0+:+startIndex+>+(val.Length+-+1)+?+val.Length+:+startIndex);
++++}

++++public+static+String+Substring(this+String+val,+int+startIndex,+int+length,+bool+handleIndexException)
++++{
++++++++if+(!handleIndexException)
++++++++{+//handleIndexException+is+false+so+call+the+base+method
++++++++++++return+val.Substring(startIndex,+length);
++++++++}
++++++++if+(string.IsNullOrEmpty(val))
++++++++{
++++++++++++return+val;
++++++++}
++++++++int+newfrom,+newlth,+instrlength+=+val.Length;
++++++++if+(length+<+0)+//length+is+negative
++++++++{
++++++++++++newfrom+=+startIndex+%2B+length;
++++++++++++newlth+=+-1+*+length;
++++++++}
++++++++else+//length+is+positive
++++++++{
++++++++++++newfrom+=+startIndex;
++++++++++++newlth+=+length;
++++++++}
++++++++if+(newfrom+%2B+newlth+<+0+%7C%7C+newfrom+>+instrlength+-+1)
++++++++{
++++++++++++return+string.Empty;
++++++++}
++++++++if+(newfrom+<+0)
++++++++{
++++++++++++newlth+=+newfrom+%2B+newlth;
++++++++++++newfrom+=+0;
++++++++}
++++++++return+val.Substring(newfrom,+Math.Min(newlth,+instrlength+-+newfrom));
++++}|code-block|syntax|javascript|947043|早在2010年5月，我就在http://jagdale.blogspot.com/2010/05/substring-extension-method-that-does.html上发表了关于这一点的博客|947044|entityMap|0|LINK|mutability|MUTABLE|url|https://dotnetfiddle.net/m1mSH9|1|http://jagdale.blogspot.com/2010/05/substring-extension-method-that-does.html^0|3K|V|0|0|0|0|D|25|1|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|6|7|10|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|11|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|12|8|@]|9|@$A|13|B|14|1|15]]|C|$]]|$1|M|3|-4|5|6|7|16|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]|U|$5|P|Q|R|C|$S|V]]]]

The .NET Substring method is fraught with peril. I developed extension methods that handle a wide variety of scenarios. The nice thing is it preserves the original behavior, but when you add an additional "true" parameter, it then resorts to the extension method to handle the exception, and returns the most logical values, based on the index and length. For example, if length is negative, and counts backward. You can look at the test results with wide variety of values on the fiddle at: <a href="https://dotnetfiddle.net/m1mSH9" rel="nofollow noreferrer">https://dotnetfiddle.net/m1mSH9</a>. This will give you a clear idea on how it resolves substrings.

I always add these methods to all my projects, and never have to worry about code breaking, because something changed and the index is invalid. Below is the code. 

<pre><code> public static String Substring(this String val, int startIndex, bool handleIndexException)
 {
 if (!handleIndexException)
 { //handleIndexException is false so call the base method
 return val.Substring(startIndex);
 }
 if (string.IsNullOrEmpty(val))
 {
 return val;
 }
 return val.Substring(startIndex &lt; 0 ? 0 : startIndex &gt; (val.Length - 1) ? val.Length : startIndex);
 }

 public static String Substring(this String val, int startIndex, int length, bool handleIndexException)
 {
 if (!handleIndexException)
 { //handleIndexException is false so call the base method
 return val.Substring(startIndex, length);
 }
 if (string.IsNullOrEmpty(val))
 {
 return val;
 }
 int newfrom, newlth, instrlength = val.Length;
 if (length &lt; 0) //length is negative
 {
 newfrom = startIndex + length;
 newlth = -1 * length;
 }
 else //length is positive
 {
 newfrom = startIndex;
 newlth = length;
 }
 if (newfrom + newlth &lt; 0 || newfrom &gt; instrlength - 1)
 {
 return string.Empty;
 }
 if (newfrom &lt; 0)
 {
 newlth = newfrom + newlth;
 newfrom = 0;
 }
 return val.Substring(newfrom, Math.Min(newlth, instrlength - newfrom));
 }
</code></pre>

I blogged about this back in May 2010 at: <a href="http://jagdale.blogspot.com/2010/05/substring-extension-method-that-does.html" rel="nofollow noreferrer">http://jagdale.blogspot.com/2010/05/substring-extension-method-that-does.html</a>

blocks|key|947049|text|使用C#+8|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|947050|public+static+string+TruncateLongString(this+string+str,+int+maxLength)
{
++++if+(string.IsNullOrEmpty(str))+return+str;

++++return+str[..+Math.Min(str.Length,+maxLength)];
}|code-block|syntax|javascript|947051|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-8.0/ranges^0|2|4|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]]]]

With the <a href="https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-8.0/ranges" rel="nofollow noreferrer">C# 8</a>
<pre><code>public static string TruncateLongString(this string str, int maxLength)
{
 if (string.IsNullOrEmpty(str)) return str;

 return str[.. Math.Min(str.Length, maxLength)];
}
</code></pre>

blocks|key|946737|text|substring(int+startpos,+int+lenght);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|946738|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>substring(int startpos, int lenght);
</code></pre>

blocks|key|1160695|text|string.Substring(0，n)；//+0-起始索引，n-字符数|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1160696|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|$]]

string.Substring(0,n); // 0 - start index and n - number of characters

I'd like to write an extension method to the <code>String</code> class so that if the input string to is longer than the provided length <code>N</code>, only the first <code>N</code> characters are to be displayed.

Here's how it looks like:

<pre><code>public static string TruncateLongString(this string str, int maxLength)
{
 if (str.Length &lt;= maxLength)
 return str;
 else
 //return the first maxLength characters 
}
</code></pre>

What <code>String.*()</code> method can I use to get only the first <code>N</code> characters of <code>str</code>?

What method in the String class returns only the first N characters?

我想为String类编写一个扩展方法，以便如果输入字符串to比提供的长度N长，则只显示前N字符。它看起来是这样的：public static string TruncateLongString(this string str, int maxLength){ if (str.Length <= maxLength) return str; else //re

问String类中的哪个方法只返回前N个字符？
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回答 11

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问String类中的哪个方法只返回前N个字符？
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