blocks|key|2989191|text|使用String.Substring()+(details+here)切割左侧部分，然后替换，然后是右侧部分。使用索引，直到正确为止:)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2989192|类似于：|2989193|string+replacement=original.Substring(0,start)%2B
++++rep%2Boriginal.Substring(start%2Brep.Length);|code-block|syntax|javascript|2989194|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/system.string.substring.aspx^0|2|I|U|4|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@$9|X|A|Y|1|Z]]|E|$]]|$1|F|3|G|5|6|7|10|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|11|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

Use <code>String.Substring()</code> (details <a href="http://msdn.microsoft.com/en-us/library/system.string.substring.aspx" rel="noreferrer">here</a>) to cut left part, then your replacement, then right part. Play with indexes until you get it right :)

Something like:

<pre><code>string replacement=original.Substring(0,start)+
 rep+original.Substring(start+rep.Length);
</code></pre>

blocks|key|3202774|text|在字符串中添加和删除范围的最简单方法是使用StringBuilder。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3202775|var+theString+=+"ABCDEFGHIJ";
var+aStringBuilder+=+new+StringBuilder(theString);
aStringBuilder.Remove(3,+2);
aStringBuilder.Insert(3,+"ZX");
theString+=+aStringBuilder.ToString();|code-block|syntax|javascript|3202776|另一种选择是使用String.Substring，但我认为StringBuilder代码更具可读性。|3202777|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/system.text.stringbuilder.aspx|1|http://msdn.microsoft.com/en-us/library/aka44szs.aspx^0|L|D|L|D|0|0|0|8|G|T|D|8|G|1|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|F|3|G|5|H|7|12|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|13|8|@$9|14|A|15|B|C]|$9|16|A|17|B|C]]|D|@$9|18|A|19|1|1A]]|E|$]]|$1|M|3|-4|5|6|7|1B|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]|U|$5|P|Q|R|E|$S|V]]]]

The easiest way to add and remove ranges in a string is to use the <a href="http://msdn.microsoft.com/en-us/library/system.text.stringbuilder.aspx"><code>StringBuilder</code></a>.

<pre><code>var theString = "ABCDEFGHIJ";
var aStringBuilder = new StringBuilder(theString);
aStringBuilder.Remove(3, 2);
aStringBuilder.Insert(3, "ZX");
theString = aStringBuilder.ToString();
</code></pre>

An alternative is to use <a href="http://msdn.microsoft.com/en-us/library/aka44szs.aspx"><code>String.Substring</code></a>, but I think the <code>StringBuilder</code> code gets more readable.

blocks|key|2989280|text|您可以尝试链接以下内容：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2989281|string+str+=+"ABCDEFGHIJ";
str+=+str.Substring(0,+2)+%2B+"ZX"+%2B+str.Substring(5);|code-block|syntax|javascript|2989282|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 could try something link this:

<pre><code>string str = "ABCDEFGHIJ";
str = str.Substring(0, 2) + "ZX" + str.Substring(5);
</code></pre>

blocks|key|3202856|text|++++++++string+s+=+"ABCDEFG";
++++++++string+t+=+"st";
++++++++s+=+s.Remove(4,+t.Length);
++++++++s+=+s.Insert(4,+t);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|3202857|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 s = "ABCDEFG";
 string t = "st";
 s = s.Remove(4, t.Length);
 s = s.Insert(4, t);
</code></pre>

blocks|key|3202859|text|string+s+=+"ABCDEFGH";
s=+s.Remove(3,+2).Insert(3,+"ZX");|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|3202860|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 s = "ABCDEFGH";
s= s.Remove(3, 2).Insert(3, "ZX");
</code></pre>

blocks|key|3202881|text|我相信最简单的方法是这样的：(没有字符串构建器)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3202882|string+myString+=+"ABCDEFGHIJ";
char[]+replacementChars+=+{'Z',+'X'};
byte+j+=+0;

for+(byte+i+=+3;+i+<=+4;+i%2B%2B,+j%2B%2B)++
{+++++++++++++++++++
myString+=+myString.Replace(myString[i],+replacementChars[j]);++
}|code-block|syntax|javascript|3202883|这是因为string类型的变量可以被视为char变量的数组。例如，您可以将名为"myString“的字符串变量的第二个字符引用为myString1|3202884|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I believe the simplest way would be this:(without stringbuilder)

<pre><code>string myString = "ABCDEFGHIJ";
char[] replacementChars = {'Z', 'X'};
byte j = 0;

for (byte i = 3; i &lt;= 4; i++, j++) 
{ 
myString = myString.Replace(myString[i], replacementChars[j]); 
}
</code></pre>

This works because a variable of type string can be treated as an array of char variables.
You can, for example refer to the second character of a string variable with name "myString" as myString[1]

blocks|key|283464|text|就像其他人提到的那样，Substring()函数的存在是有原因的：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|283465|static+void+Main(string[]+args)
{
++++string+input+=+"ABCDEFGHIJ";

++++string+output+=+input.Overwrite(3,+"ZX");+//+4th+position+has+index+3
++++//+ABCZXFGHIJ
}

public+static+string+Overwrite(this+string+text,+int+position,+string+new_text)
{
++++return+text.Substring(0,+position)+%2B+new_text+%2B+text.Substring(position+%2B+new_text.Length);
}|code-block|syntax|javascript|283466|此外，我将其与StringBuilder解决方案进行了对比，得到了900次测试，而不是875次。所以它稍微慢一点。|283467|entityMap^0|B|B|0|0|7|D|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|N|$]]

Like other have mentioned the <code>Substring()</code> function is there for a reason:

<pre><code>static void Main(string[] args)
{
 string input = "ABCDEFGHIJ";

 string output = input.Overwrite(3, "ZX"); // 4th position has index 3
 // ABCZXFGHIJ
}

public static string Overwrite(this string text, int position, string new_text)
{
 return text.Substring(0, position) + new_text + text.Substring(position + new_text.Length);
}
</code></pre>

Also I timed this against the <code>StringBuilder</code> solution and got 900 tics vs. 875. So it is slightly slower.

blocks|key|2989390|text|作为一种扩展方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2989391|public+static+class+StringBuilderExtension
{
++++public+static+string+SubsituteString(this+string+OriginalStr,+int+index,+int+length,+string+SubsituteStr)
++++{
++++++++return+new+StringBuilder(OriginalStr).Remove(index,+length).Insert(index,+SubsituteStr).ToString();
++++}
}|code-block|syntax|javascript|2989392|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|$]]

As an extension method.

<pre><code>public static class StringBuilderExtension
{
 public static string SubsituteString(this string OriginalStr, int index, int length, string SubsituteStr)
 {
 return new StringBuilder(OriginalStr).Remove(index, length).Insert(index, SubsituteStr).ToString();
 }
}
</code></pre>

blocks|key|281465|text|ReplaceAt(整型索引，整型长度，字符串替换)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|281466|下面是一个不使用StringBuilder或子字符串的扩展方法。此方法还允许替换字符串超出源字符串的长度。|281467|////+str+-+the+source+string
////+index-+the+start+location+to+replace+at+(0-based)
////+length+-+the+number+of+characters+to+be+removed+before+inserting
////+replace+-+the+string+that+is+replacing+characters
public+static+string+ReplaceAt(this+string+str,+int+index,+int+length,+string+replace)
{
++++return+str.Remove(index,+Math.Min(length,+str.Length+-+index))
++++++++++++.Insert(index,+replace);
}|code-block|syntax|javascript|281468|使用此函数时，如果希望整个替换字符串替换尽可能多的字符，则将长度设置为替换字符串的长度：|281469|"0123456789".ReplaceAt(7,+5,+"Hello")+=+"0123456Hello"|281470|否则，您可以指定要删除的字符数：|281471|"0123456789".ReplaceAt(2,+2,+"Hello")+=+"01Hello456789"|281472|如果将长度指定为0，则此函数的作用与insert函数相同：|281473|"0123456789".ReplaceAt(4,+0,+"Hello")+=+"0123Hello456789"|281474|我猜这会更有效，因为StringBuilder类不需要初始化，而且它使用了更基本的操作。如果我错了，请纠正我。:)|281475|entityMap^0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Z|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|10|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|11|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|12|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|13|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|14|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|15|8|@]|9|@]|A|$]]|$1|S|3|T|5|F|7|16|8|@]|9|@]|A|$G|H]]|$1|U|3|V|5|6|7|17|8|@]|9|@]|A|$]]|$1|W|3|-4|5|6|7|18|8|@]|9|@]|A|$]]]|X|$]]

<h2>ReplaceAt(int index, int length, string replace)</h2>
Here's an extension method that doesn't use StringBuilder or Substring. This method also allows the replacement string to extend past the length of the source string.
<pre><code>//// str - the source string
//// index- the start location to replace at (0-based)
//// length - the number of characters to be removed before inserting
//// replace - the string that is replacing characters
public static string ReplaceAt(this string str, int index, int length, string replace)
{
 return str.Remove(index, Math.Min(length, str.Length - index))
 .Insert(index, replace);
}
</code></pre>
When using this function, if you want the entire replacement string to replace as many characters as possible, then set length to the length of the replacement string:
<pre><code>&quot;0123456789&quot;.ReplaceAt(7, 5, &quot;Hello&quot;) = &quot;0123456Hello&quot;
</code></pre>
Otherwise, you can specify the amount of characters that will be removed:
<pre><code>&quot;0123456789&quot;.ReplaceAt(2, 2, &quot;Hello&quot;) = &quot;01Hello456789&quot;
</code></pre>
If you specify the length to be 0, then this function acts just like the insert function:
<pre><code>&quot;0123456789&quot;.ReplaceAt(4, 0, &quot;Hello&quot;) = &quot;0123Hello456789&quot;
</code></pre>
I guess this is more efficient since the StringBuilder class need not be initialized and since it uses more basic operations. Please correct me if I am wrong. :)

blocks|key|3202981|text|在这篇文章的帮助下，我创建了以下带有附加长度检查的函数|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3202982|public+string+ReplaceStringByIndex(string+original,+string+replaceWith,+int+replaceIndex)
{
++++if+(original.Length+>=+(replaceIndex+%2B+replaceWith.Length))
++++{
++++++++StringBuilder+rev+=+new+StringBuilder(original);
++++++++rev.Remove(replaceIndex,+replaceWith.Length);
++++++++rev.Insert(replaceIndex,+replaceWith);
++++++++return+rev.ToString();
++++}
++++else
++++{
++++++++throw+new+Exception("Wrong+lengths+for+the+operation");
++++}
}|code-block|syntax|javascript|3202983|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|$]]

With the help of this post, I create following function with additional length checks

<pre><code>public string ReplaceStringByIndex(string original, string replaceWith, int replaceIndex)
{
 if (original.Length &gt;= (replaceIndex + replaceWith.Length))
 {
 StringBuilder rev = new StringBuilder(original);
 rev.Remove(replaceIndex, replaceWith.Length);
 rev.Insert(replaceIndex, replaceWith);
 return rev.ToString();
 }
 else
 {
 throw new Exception("Wrong lengths for the operation");
 }
}
</code></pre>

blocks|key|279738|text|又是另一个|type|unstyled|depth|inlineStyleRanges|entityRanges|data|279739|++++public+static+string+ReplaceAtPosition(this+string+self,+int+position,+string+newValue)++++++++
++++{
++++++++return+self.Remove(position,+newValue.Length).Insert(position,+newValue);+
++++}|code-block|syntax|javascript|279740|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|$]]

Yet another

<pre><code> public static string ReplaceAtPosition(this string self, int position, string newValue) 
 {
 return self.Remove(position, newValue.Length).Insert(position, newValue); 
 }
</code></pre>

blocks|key|281509|text|最好使用String.substr()。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|281510|如下所示：|281511|ReplString+=+GivenStr.substr(0,+PostostarRelStr)
+++++++++++%2B+GivenStr(PostostarRelStr,+ReplString.lenght());|code-block|syntax|javascript|281512|entityMap^0|4|F|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|R|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|S|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

It's better to use the <code>String.substr()</code>. 

Like this:

<pre><code>ReplString = GivenStr.substr(0, PostostarRelStr)
 + GivenStr(PostostarRelStr, ReplString.lenght());
</code></pre>

blocks|key|283573|text|如果字符串包含Unicode+char+(如Emojis)，则所有其他答案都不起作用，因为Unicode+char比char重了更多字节。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|283574|283575|示例:表情符号'‘转换为字节后，其权重将相当于2个字符。因此，如果unicode字符被放在字符串的开头，offset参数将被移位)。|blockquote|offset|length|style|CODE|283576|283577|283578|使用this+topic，我扩展了StringInfo类，通过保持Nick+Miller算法的位置来替换，以避免这种情况：|283579|public+static+class+StringInfoUtils
{
++++public+static+string+ReplaceByPosition(this+string+str,+string+replaceBy,+int+offset,+int+count)
++++{
++++++++return+new+StringInfo(str).ReplaceByPosition(replaceBy,+offset,+count).String;
++++}

++++public+static+StringInfo+ReplaceByPosition(this+StringInfo+str,+string+replaceBy,+int+offset,+int+count)
++++{
++++++++return+str.RemoveByTextElements(offset,+count).InsertByTextElements(offset,+replaceBy);
++++}

++++public+static+StringInfo+RemoveByTextElements(this+StringInfo+str,+int+offset,+int+count)
++++{
++++++++return+new+StringInfo(string.Concat(
++++++++++++str.SubstringByTextElements(0,+offset),
++++++++++++offset+%2B+count+<+str.LengthInTextElements
++++++++++++++++?+str.SubstringByTextElements(offset+%2B+count,+str.LengthInTextElements+-+count+-+offset)
++++++++++++++++:+""
++++++++++++));
++++}
++++public+static+StringInfo+InsertByTextElements(this+StringInfo+str,+int+offset,+string+insertStr)
++++{
++++++++if+(string.IsNullOrEmpty(str?.String))
++++++++++++return+new+StringInfo(insertStr);
++++++++return+new+StringInfo(string.Concat(
++++++++++++str.SubstringByTextElements(0,+offset),
++++++++++++insertStr,
++++++++++++str.LengthInTextElements+-+offset+>+0+?+str.SubstringByTextElements(offset,+str.LengthInTextElements+-+offset)+:+""
++++++++));
++++}
}|code-block|syntax|javascript|283580|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/5656472/what-does-the-net-string-length-property-return-surrogate-neutral-length-or-co^0|0|0|1G|6|0|0|0|2|A|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|11|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|12|8|@$F|13|G|14|H|I]]|9|@]|A|$]]|$1|J|3|-4|5|6|7|15|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|16|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|17|8|@]|9|@$F|18|G|19|1|1A]]|A|$]]|$1|N|3|O|5|P|7|1B|8|@]|9|@]|A|$Q|R]]|$1|S|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]]|T|$U|$5|V|W|X|A|$Y|Z]]]]

All others answers don't work if the string contains Unicode char (like Emojis) because an Unicode char weight more bytes than a char.

<blockquote>
 Example : the emoji '' converted to bytes, will weight the equivalent of 2 chars. So, if the unicode char is placed at the beginning of your string, <code>offset</code> parameter will be shifted).
</blockquote>

With <a href="https://stackoverflow.com/questions/5656472/what-does-the-net-string-length-property-return-surrogate-neutral-length-or-co">this topic</a>, i extend the StringInfo class to Replace by position keeping the Nick Miller's algorithm to avoid that :

<pre><code>public static class StringInfoUtils
{
 public static string ReplaceByPosition(this string str, string replaceBy, int offset, int count)
 {
 return new StringInfo(str).ReplaceByPosition(replaceBy, offset, count).String;
 }

 public static StringInfo ReplaceByPosition(this StringInfo str, string replaceBy, int offset, int count)
 {
 return str.RemoveByTextElements(offset, count).InsertByTextElements(offset, replaceBy);
 }

 public static StringInfo RemoveByTextElements(this StringInfo str, int offset, int count)
 {
 return new StringInfo(string.Concat(
 str.SubstringByTextElements(0, offset),
 offset + count &lt; str.LengthInTextElements
 ? str.SubstringByTextElements(offset + count, str.LengthInTextElements - count - offset)
 : ""
 ));
 }
 public static StringInfo InsertByTextElements(this StringInfo str, int offset, string insertStr)
 {
 if (string.IsNullOrEmpty(str?.String))
 return new StringInfo(insertStr);
 return new StringInfo(string.Concat(
 str.SubstringByTextElements(0, offset),
 insertStr,
 str.LengthInTextElements - offset &gt; 0 ? str.SubstringByTextElements(offset, str.LengthInTextElements - offset) : ""
 ));
 }
}
</code></pre>

blocks|key|279809|text|我正在寻找一个满足以下要求的解决方案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|279810|279811|仅使用单行表达式|ordered-list-item|279812|仅使用系统内置方法(无自定义实现的实用程序)|279813|279814|解决方案1|279815|最适合我的解决方案是：|279816|//+replace+`oldString[i]`+with+`c`
string+newString+=+new+StringBuilder(oldString).Replace(oldString[i],+c,+i,+1).ToString();|code-block|syntax|javascript|279817|这使用StringBuilder.Replace(oldChar,+newChar,+position,+count)|offset|length|style|CODE|279818|解决方案2|279819|另一种满足我要求的解决方案是使用Substring进行连接：|279820|string+newString+=+oldStr.Substring(0,+i)+%2B+c+%2B+oldString.Substring(i%2B1,+oldString.Length);|279821|这也没问题。我猜它在性能方面不如第一个(由于不必要的字符串连接)。但是过早的优化是万恶之源。|279822|所以选一个你最喜欢的:)|279823|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.microsoft.com/en-us/dotnet/api/system.text.stringbuilder.replace?view=netframework-4.7.1#System_Text_StringBuilder_Replace_System_Char_System_Char_System_Int32_System_Int32_^0|0|0|0|0|0|0|0|0|3|1K|3|1K|0|0|0|G|9|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1F|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|1G|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|1H|8|@]|9|@]|A|$]]|$1|F|3|G|5|E|7|1I|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|1J|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|1K|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|1L|8|@]|9|@]|A|$]]|$1|M|3|N|5|O|7|1M|8|@]|9|@]|A|$P|Q]]|$1|R|3|S|5|6|7|1N|8|@$T|1O|U|1P|V|W]]|9|@$T|1Q|U|1R|1|1S]]|A|$]]|$1|X|3|Y|5|6|7|1T|8|@]|9|@]|A|$]]|$1|Z|3|10|5|6|7|1U|8|@$T|1V|U|1W|V|W]]|9|@]|A|$]]|$1|11|3|12|5|O|7|1X|8|@]|9|@]|A|$P|Q]]|$1|13|3|14|5|6|7|1Y|8|@]|9|@]|A|$]]|$1|15|3|16|5|6|7|1Z|8|@]|9|@]|A|$]]|$1|17|3|-4|5|6|7|20|8|@]|9|@]|A|$]]]|18|$19|$5|1A|1B|1C|A|$1D|1E]]]]

I was looking for a solution with following requirements:

<ol>
<li>use only a single, one-line expression</li>
<li>use only system builtin methods (no custom implemented utility)</li>
</ol>

<h1>Solution 1</h1>

The solution that best suits me is this:

<pre><code>// replace `oldString[i]` with `c`
string newString = new StringBuilder(oldString).Replace(oldString[i], c, i, 1).ToString();
</code></pre>

This uses <a href="https://docs.microsoft.com/en-us/dotnet/api/system.text.stringbuilder.replace?view=netframework-4.7.1#System_Text_StringBuilder_Replace_System_Char_System_Char_System_Int32_System_Int32_" rel="nofollow noreferrer"><code>StringBuilder.Replace(oldChar, newChar, position, count)</code></a>

<h1>Solution 2</h1>

The other solution that satisfies my requirements is to use <code>Substring</code> with concatenation:

<pre><code>string newString = oldStr.Substring(0, i) + c + oldString.Substring(i+1, oldString.Length);
</code></pre>

This is OK too. I guess it's not as efficient as the first one performance wise (due to unnecessary string concatenation). But premature optimization is the root of all evil. 

So pick the one that you like the most :)

blocks|key|281548|text|如果你关心的是性能，那么这里你要避免的就是分配。如果您使用的是.Net核心2.1%2B+(或尚未发布的.Net标准2.1)，则可以使用the+string.Create+method|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|281549|public+static+string+ReplaceAt(this+string+str,+int+index,+int+length,+string+replace)
{
++++return+string.Create(str.Length+-+length+%2B+replace.Length,+(str,+index,+length,+replace),
++++++++(span,+state)+=>
++++++++{
++++++++++++state.str.AsSpan().Slice(0,+state.index).CopyTo(span);
++++++++++++state.replace.AsSpan().CopyTo(span.Slice(state.index));
++++++++++++state.str.AsSpan().Slice(state.index+%2B+state.length).CopyTo(span.Slice(state.index+%2B+state.replace.Length));
++++++++});
}|code-block|syntax|javascript|281550|这种方法比其他方法更难理解，但它是唯一一种每次调用只分配一个对象的方法:新创建的字符串。|281551|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.microsoft.com/en-us/dotnet/api/system.string.create?view=netcore-2.1^0|1X|D|1T|O|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@$9|X|A|Y|1|Z]]|E|$]]|$1|F|3|G|5|H|7|10|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|11|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

If you care about performance, then the thing you want to avoid here are allocations. And if you're on .Net Core 2.1+ (or the, as yet unreleased, .Net Standard 2.1), then you can, by using <a href="https://docs.microsoft.com/en-us/dotnet/api/system.string.create?view=netcore-2.1" rel="noreferrer">the <code>string.Create</code> method</a>:

<pre><code>public static string ReplaceAt(this string str, int index, int length, string replace)
{
 return string.Create(str.Length - length + replace.Length, (str, index, length, replace),
 (span, state) =&gt;
 {
 state.str.AsSpan().Slice(0, state.index).CopyTo(span);
 state.replace.AsSpan().CopyTo(span.Slice(state.index));
 state.str.AsSpan().Slice(state.index + state.length).CopyTo(span.Slice(state.index + state.replace.Length));
 });
}
</code></pre>

This approach is harder to understand than the alternatives, but it's the only one that will allocate only one object per call: the newly created string.

blocks|key|281600|text|string+myString+=+"ABCDEFGHIJ";
string+modifiedString+=+new+StringBuilder(myString){[3]='Z',+[4]='X'}.ToString();|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|281601|让我解释一下我的解决方案。|unstyled|281602|考虑到在两个特定位置(“position+4+to+position+5”)使用两个字符‘Z’和‘X’更改字符串的问题语句，并且要求使用位置索引来更改字符串而不是string+Replace()方法(可能是因为实际字符串中某些字符重复的可能性)，我倾向于使用最低限度的方法来实现该目标，而不是使用Substring()和string+Concat()或string+Remove()和Insert()方法。尽管所有这些解决方案都将服务于实现相同目标的目的，但它仅取决于个人选择和以最低限度的方法解决问题的哲学。|offset|length|style|CODE|281603|回到上面提到的我的解决方案，如果我们仔细观察string和StringBuilder，它们都在内部将给定的字符串视为字符数组。如果我们看一下StringBuilder的实现，它维护一个类似于“internal+char[]+m_ChunkChars;”的内部变量来捕获给定的字符串。现在由于这是一个内部变量，我们不能直接访问它。对于外部世界，为了能够访问和更改字符数组，StringBuilder通过索引器属性公开它们，如下所示|281604|++++[IndexerName("Chars")]
++++public+char+this[int+index]
++++{
++++++get
++++++{
++++++++StringBuilder+stringBuilder+=+this;
++++++++do
++++++++{
++++++++++//+…+some+code
++++++++++++return+stringBuilder.m_ChunkChars[index1];
++++++++++//+…+some+more+code
++++++++}
++++++}
++++++set
++++++{
++++++++StringBuilder+stringBuilder+=+this;
++++++++do
++++++++{
++++++++++++//…+some+code
++++++++++++stringBuilder.m_ChunkChars[index1]+=+value;
++++++++++++return;
++++++++++++//+….+Some+more+code
++++++++}
++++++}
++++}|281605|上面提到的我的解决方案利用这个索引器功能来直接改变内部维护的字符数组，这是IMO的高效和最低限度的。|281606|顺便说一句，我们可以更细致地重写上面的解决方案，如下所示|281607|+string+myString+=+"ABCDEFGHIJ";
+StringBuilder+tempString+=+new+StringBuilder(myString);
+tempString[3]+=+'Z';
+tempString[4]+=+'X';
+string+modifiedString+=+tempString.ToString();|281608|在此上下文中还想提到，在string情况下，它也有索引器属性作为公开其内部字符数组的方法，但在这种情况下，它只有Getter属性(没有Setter)，因为字符串本质上是不可变的。这就是为什么我们需要使用StringBuilder来改变字符数组。|281609|[IndexerName("Chars")]
public+extern+char+this[int+index]+{+[SecuritySafeCritical,+__DynamicallyInvokable,+MethodImpl(MethodImplOptions.InternalCall)]+get;+}|281610|最后但并非最不重要的是，这个解决方案最适合于这个特定的问题，在这个问题中，要求只用一个已知的位置索引预先替换几个字符。当需要更改相当长的字符串时，它可能不是最合适的，即要更改的字符数很大。|281611|entityMap^0|0|0|44|B|4N|8|53|8|5C|8|0|M|6|T|D|1Y|D|2O|T|55|D|0|0|0|0|0|C|6|2T|D|0|0|0^^$0|@$1|2|3|4|5|6|7|14|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|15|8|@]|9|@]|A|$]]|$1|G|3|H|5|F|7|16|8|@$I|17|J|18|K|L]|$I|19|J|1A|K|L]|$I|1B|J|1C|K|L]|$I|1D|J|1E|K|L]]|9|@]|A|$]]|$1|M|3|N|5|F|7|1F|8|@$I|1G|J|1H|K|L]|$I|1I|J|1J|K|L]|$I|1K|J|1L|K|L]|$I|1M|J|1N|K|L]|$I|1O|J|1P|K|L]]|9|@]|A|$]]|$1|O|3|P|5|6|7|1Q|8|@]|9|@]|A|$B|C]]|$1|Q|3|R|5|F|7|1R|8|@]|9|@]|A|$]]|$1|S|3|T|5|F|7|1S|8|@]|9|@]|A|$]]|$1|U|3|V|5|6|7|1T|8|@]|9|@]|A|$B|C]]|$1|W|3|X|5|F|7|1U|8|@$I|1V|J|1W|K|L]|$I|1X|J|1Y|K|L]]|9|@]|A|$]]|$1|Y|3|Z|5|6|7|1Z|8|@]|9|@]|A|$B|C]]|$1|10|3|11|5|F|7|20|8|@]|9|@]|A|$]]|$1|12|3|-4|5|F|7|21|8|@]|9|@]|A|$]]]|13|$]]

<pre><code>string myString = "ABCDEFGHIJ";
string modifiedString = new StringBuilder(myString){[3]='Z', [4]='X'}.ToString();
</code></pre>

Let me explain my solution. 
Given the problem statement of altering a string in its two specific position (“position 4 to position 5”) with two character ‘Z’ and ‘X’ and the ask is to use the position index to alter the string and not string Replace() method(may be because of the possibility of repetition of some characters in the actual string), I would prefer to use minimalist approach to achieve the goal over using <code>Substring()</code> and string <code>Concat()</code> or string <code>Remove()</code> and <code>Insert()</code> approach. Though all those solutions will serve the purpose in attaining the same goal, but it just depends on personal choice and philosophy of settling with minimalist approach. 
Coming back to my solution mention above, if we take a closer look of <code>string</code> and <code>StringBuilder</code>, both of them internally treats a given string as an array of characters. If we look at the implementation of <code>StringBuilder</code> it maintains an internal variable something like “<code>internal char[] m_ChunkChars;</code>” to capture the given string. Now since this is an internal variable, we cannot directly access the same. For external world, to be able to access and alter that character array, <code>StringBuilder</code> exposes them through indexer property which looks something like below 

<pre><code> [IndexerName("Chars")]
 public char this[int index]
 {
 get
 {
 StringBuilder stringBuilder = this;
 do
 {
 // … some code
 return stringBuilder.m_ChunkChars[index1];
 // … some more code
 }
 }
 set
 {
 StringBuilder stringBuilder = this;
 do
 {
 //… some code
 stringBuilder.m_ChunkChars[index1] = value;
 return;
 // …. Some more code
 }
 }
 }
</code></pre>

My solution mentioned above leverage this indexer capability to directly alter the internally maintained character array which IMO is efficient and minimalist.

BTW; we can rewrite the above solution more elaborately something like below 

<pre><code> string myString = "ABCDEFGHIJ";
 StringBuilder tempString = new StringBuilder(myString);
 tempString[3] = 'Z';
 tempString[4] = 'X';
 string modifiedString = tempString.ToString();
</code></pre>

In this context also would like to mention that in case of <code>string</code> it also have indexer property as a means to expose its internal character array, but in this case it only has Getter property (and no Setter) as string is immutable in nature. And that is why we need to use <code>StringBuilder</code> to alter the character array.

<pre><code>[IndexerName("Chars")]
public extern char this[int index] { [SecuritySafeCritical, __DynamicallyInvokable, MethodImpl(MethodImplOptions.InternalCall)] get; }
</code></pre>

And last but not the least this solution is only best fit for this specific problem where the ask is to replace only few characters with a known position index upfront. It may not be the best fit when the requirement is to alter a fairly lengthy string i.e. number of characters to alter are large in numbers.

blocks|key|278018|text|String+timestamp+=+"2019-09-18+21.42.05.000705";
String+sub1+=+timestamp.substring(0,+19).replace('.',+':');+
String+sub2+=+timestamp.substring(19,+timestamp.length());
System.out.println("Original+String+"%2B+timestamp);++++++
System.out.println("Replaced+Value+"%2B+sub1%2Bsub2);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|278019|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 timestamp = "2019-09-18 21.42.05.000705";
String sub1 = timestamp.substring(0, 19).replace('.', ':'); 
String sub2 = timestamp.substring(19, timestamp.length());
System.out.println("Original String "+ timestamp); 
System.out.println("Replaced Value "+ sub1+sub2);
</code></pre>

blocks|key|281624|text|下面是一个简单的扩展方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|281625|++++public+static+class+StringBuilderExtensions
++++{
++++++++public+static+StringBuilder+Replace(this+StringBuilder+sb,+int+position,+string+newString)
++++++++++++=>+sb.Replace(position,+newString.Length,+newString);

++++++++public+static+StringBuilder+Replace(this+StringBuilder+sb,+int+position,+int+length,+string+newString)
++++++++++++=>+(newString.Length+<=+length)
++++++++++++++++?+sb.Remove(position,+newString.Length).Insert(position,+newString)
++++++++++++++++:+sb.Remove(position,+length).Insert(position,+newString.Substring(0,+length));
++++}|code-block|syntax|javascript|281626|像这样使用它：|281627|var+theString+=+new+string('+',+10);
var+sb+=+new+StringBuilder(theString);
sb.Replace(5,+"foo");
return+sb.ToString();|281628|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Here is a simple extension method:

<pre class="lang-cs prettyprint-override"><code> public static class StringBuilderExtensions
 {
 public static StringBuilder Replace(this StringBuilder sb, int position, string newString)
 =&gt; sb.Replace(position, newString.Length, newString);

 public static StringBuilder Replace(this StringBuilder sb, int position, int length, string newString)
 =&gt; (newString.Length &lt;= length)
 ? sb.Remove(position, newString.Length).Insert(position, newString)
 : sb.Remove(position, length).Insert(position, newString.Substring(0, length));
 }
</code></pre>

Use it like this:

<pre class="lang-cs prettyprint-override"><code>var theString = new string(' ', 10);
var sb = new StringBuilder(theString);
sb.Replace(5, "foo");
return sb.ToString();
</code></pre>

blocks|key|2989705|text|我这样做|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2989706|Dim+QTT+As+Double
++++++++++++++++If+IsDBNull(dr.Item(7))+Then
++++++++++++++++++++QTT+=+0
++++++++++++++++Else
++++++++++++++++++++Dim+value+As+String+=+dr.Item(7).ToString()
++++++++++++++++++++Dim+posicpoint+As+Integer+=+value.LastIndexOf(".")
++++++++++++++++++++If+posicpoint+>+0+Then
++++++++++++++++++++++++Dim+v+As+New+Text.StringBuilder(value)
++++++++++++++++++++++++v.Remove(posicpoint,+1)
++++++++++++++++++++++++v.Insert(posicpoint,+",")
++++++++++++++++++++++++QTT+=+Convert.ToDouble(v.ToString())
++++++++++++++++++++Else
++++++++++++++++++++++++QTT+=+Convert.ToDouble(dr.Item(7).ToString())
++++++++++++++++++++End+If
++++++++++++++++++++Console.WriteLine(QTT.ToString())
++++++++++++++++End+If|code-block|syntax|javascript|2989707|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|$]]

I do this
<pre><code>Dim QTT As Double
 If IsDBNull(dr.Item(7)) Then
 QTT = 0
 Else
 Dim value As String = dr.Item(7).ToString()
 Dim posicpoint As Integer = value.LastIndexOf(&quot;.&quot;)
 If posicpoint &gt; 0 Then
 Dim v As New Text.StringBuilder(value)
 v.Remove(posicpoint, 1)
 v.Insert(posicpoint, &quot;,&quot;)
 QTT = Convert.ToDouble(v.ToString())
 Else
 QTT = Convert.ToDouble(dr.Item(7).ToString())
 End If
 Console.WriteLine(QTT.ToString())
 End If
</code></pre>

blocks|key|281655|text|假设我们知道要替换的字符串的索引。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|281656|++++string+s+=+"ABCDEFGDEJ";
++++string+z+=+"DE";
++++int+i+=+s.IndexOf(z);
++++if(i+==+3)
++++++++s+=+s.Remove(3,z.Length).Insert(3,"ZX");
++++//s+=+ABCZXFGDEJ|code-block|syntax|javascript|281657|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|$]]

Suppose we know the index of string to be replace.
<pre><code> string s = &quot;ABCDEFGDEJ&quot;;
 string z = &quot;DE&quot;;
 int i = s.IndexOf(z);
 if(i == 3)
 s = s.Remove(3,z.Length).Insert(3,&quot;ZX&quot;);
 //s = ABCZXFGDEJ
</code></pre>

I have this string: <code>ABCDEFGHIJ</code>

I need to replace from position 4 to position 5 with the string <code>ZX</code>

It will look like this: <code>ABCZXFGHIJ</code>

But not to use with <code>string.replace("DE","ZX")</code> - I need to use with position

How can I do it?

How to replace part of string by position?

我有这个字符串：ABCDEFGHIJ我需要用字符串ZX替换从位置4到位置5它看起来像这样：ABCZXFGHIJ但不能用于string.replace("DE","ZX") -我需要使用position我该怎么做呢？

问如何通过位置替换字符串的一部分？
EN

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