获取输入字符串的位置然后在两端获取子字符串答案

【问题标题】：getting position of input string then get substring on both ends获取输入字符串的位置然后在两端获取子字符串
【发布时间】：2017-07-19 02:14:57
【问题描述】：

我有一个搜索功能，可以在文本块中搜索关键字并显示结果的截断版本。我的问题是，如果它接近尾声，它不会显示搜索到的关键字。

例如。

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引用块。通常，文本采用正方形或矩形块的形状"

我用

搜索“时代”

 text = text.Substring(0, 100) + "...";

它会返回

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

有没有办法在搜索到的关键字前后返回100个字符？

【问题讨论】：

设置最后 100 个字符：text.Substring(text.Length - 100, 100)。 text.Substring(0, 100) 返回前 100 个是正确的。
这适用于某些情况。但是，如果文本块的长度为 500 个字符，并且搜索的关键字位于位置 100 的中间位置怎么办？在这种情况下这是行不通的。
如果你不想在超过 100 个字符限制的情况下截断单词，我建议你使用StringBuilder & Split by whitespace 结合关键字搜索：joelabrahamsson.com/…。跨度>
@KevinC 你为什么删除答案

标签： c# string truncate

【解决方案1】：

       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);
            }
        }

【讨论】：

谢谢，这似乎对我有用。我确实修改了代码 ----- before = s.Substring(firstfound - 99, firstfound - (firstfound - 99));

【解决方案2】：

你可以这样做，

    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);         
    }

DEMO

【讨论】：

为了使其更通用，将“0”替换为：Math.Max(0, firstfound - 100)

【解决方案3】：

您也可以这样做，使其更具可重用性并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);
}

给你一个输出

...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...

【讨论】：