正则表达式：匹配所有内容，直到最后一个空格

Question

我想将输入字符串的长度减少到最多 20 个字符，但我不想在单词中间破坏字符串。

// show me 20 char:   12345678901234567890 
string inputString = "This is an example user input which has to be shorten at a white space";
if (inputString.length > 20)
{
    shortenString = inputString.SubString(0, 21); // <-- "This is an example us"
    
    // I need a regex to match everything until the last white space

    // final output: "This is an example"
}

Answer 1

(.{0,20})(\s|$)此正则表达式将捕获最多 20 个字符的组，以空格结尾（或字符串结尾）

Answer 2

我使用了来自@Ced 答案的正则表达式，这是最终的扩展方法：

public static string ShortenStringAtWhiteSpaceIfTooLong(this string str, int maxLen)
{
    if (str.Length <= maxLen)
    {
        return str;
    }

    string pattern = @"^(.{0," + maxLen.ToString() + @"})\s"; // <-- @"^(.{0,20})\s" 
    Regex regEx = new Regex(pattern);
    var matches = regEx.Matches(str);

    if (matches.Count > 0)
    {
        return matches[0].Value.Trim();
    }
    else
    {
        return str.Substring(0, maxLen).Trim();
    }
}