C# 获取输入字符串的位置，然后获取两端的子字符串

我有一个搜索功能，可以搜索文本块中的关键字，并显示结果的截断版本。我的问题是，它不会显示搜索的关键字，如果它接近尾声

比如说

Text=“文本块是以某种方式组合在一起的文本，例如在网页上使用段落或块引号。通常情况下，文本呈现方形或矩形块的形状”

我搜索“时代”与

它会回来的

"A block of text is text that is grouped together in some way, such as with the use of paragraphs or..."

有没有办法在搜索的关键字前后返回100个字符？

您可以这样做

    string s = "A block of text is text that is grouped together in some way, such as with the use of paragraphs or";
    string toBeSearched = "grouped";
    int firstfound = s.IndexOf(toBeSearched);       
    if (firstfound != -1 )
    {
        string before = s.Substring(0 , firstfound);
        string after = s.Substring(firstfound + toBeSearched.Length);         
    }

---

您也可以这样做，使其更易于重用，并且能够匹配关键字的多个实例

string input = "A block of text is text that is grouped together in some way, such as with the use of paragraphs or blockquotes on a Web page. Often times, the text takes on the shape of a square or rectangular block";
int buffer = 30; // how much do you want to show before/after
string match = "times";

int location = input.IndexOf(match);
while (location != -1) {
    // take buffer before and after:
    int start = location - Math.Min (buffer , location); // don't take before start
    int end = location + match.Length 
            + Math.Min( buffer,  input.Length - location - match.Length); // don't take after end
    Console.WriteLine("..." + input.Substring(start, end-start) + "...");
    location = input.IndexOf(match,location+1);
}

给你一个

...A block of text is text that is gro...
...with the use of paragraphs or blockquotes on a Web page. Often ...
...pe of a square or rectangular block...

string s=“文本块是以某种方式组合在一起的文本，例如使用段落或”；
字符串wordtoSearch=“block”；
int firstfound=s.IndexOf（wordtoSearch）；
//如果找到的第一个字母的索引大于100，则获取找到的单词前的100个字母和找到的单词后的100个字母
如果（首次发现>100）
{
字符串before=s.Substring（firstfound，firstfound-100）；
后面的字符串=s.Substring（firstfound+wordtoSearch.Length，100）；
控制台写入线（之前）；
控制台写入线（后）；
}
////如果找到的第一个字母的索引小于100，则获取找到的单词前的字母和找到的单词后的100个字母
如果（首次发现<100）
{
字符串before=s.Substring（0，firstfound）；
控制台写入线（之前）；
如果（s.长度>100）
{
后面的字符串=s.Substring（firstfound+wordtoSearch.Length，100）；
控制台写入线（后）；
}
其他的
{
后面的字符串=s.Substring（firstfound+wordtoSearch.Length）；
控制台写入线（后）；
}
}

设置最后100个字符：

text.Substring（text.Length-100100）

<代码>文本。子字符串（01100）对于返回前100个是正确的。这在某些情况下适用。然而，如果文本块长500个字符，并且搜索关键字位于位置100的中间，该怎么办？在这种情况下，这不起作用。如果您不想在单词超过100个字符限制的情况下截断单词，我建议您使用

StringBuilder

&

Split

和关键字搜索：。@KevinC为什么要删除答案为了使其更通用，请将“0”替换为：Math.Max（0，firstfind-100）谢谢，这似乎对我有用。我确实修改了代码abit---before=s.Substring（firstfound-99，firstfound-（firstfound-99））；

...A block of text is text that is gro...
...with the use of paragraphs or blockquotes on a Web page. Often ...
...pe of a square or rectangular block...

       string s = "A block of text is text that is grouped together in some way, such as with the use of paragraphs or";
       string wordtoSearch = "block";
       int firstfound = s.IndexOf(wordtoSearch);

        // If the index of the first letter found is greater than 100, get the 100 letters before the found word and 100 letters after the found word
        if (firstfound > 100)
        {
            string before = s.Substring(firstfound , firstfound-100);
            string after = s.Substring(firstfound + wordtoSearch.Length, 100);
            Console.WriteLine(before);
            Console.WriteLine(after);
        }
    //// If the index of the first letter found is less than 100, get the letters before the found word and 100 letters after the found word 
        if(firstfound < 100)
        {
            string before = s.Substring(0, firstfound);
            Console.WriteLine(before);
            if(s.Length >100)
            {
            string after = s.Substring(firstfound + wordtoSearch.Length, 100);
            Console.WriteLine(after);
            }
            else
            {
                string after = s.Substring(firstfound + wordtoSearch.Length);
                Console.WriteLine(after);
            }
        }