这段代码比这里的大多数解决方案(如果不是全部的话)都快，打包为String扩展方法，它不支持递归嵌套:

public static string GetNestedString(this string str, char start, char end)
{
    int s = -1;
    int i = -1;
    while (++i < str.Length)
        if (str[i] == start)
        {
            s = i;
            break;
        }
    int e = -1;
    while(++i < str.Length)
        if (str[i] == end)
        {
            e = i;
            break;
        }
    if (e > s)
        return str.Substring(s + 1, e - s - 1);
    return null;
}

这一个稍微长一点，也慢一点，但它处理递归嵌套更漂亮:

public static string GetNestedString(this string str, char start, char end)
{
    int s = -1;
    int i = -1;
    while (++i < str.Length)
        if (str[i] == start)
        {
            s = i;
            break;
        }
    int e = -1;
    int depth = 0;
    while (++i < str.Length)
        if (str[i] == end)
        {
            e = i;
            if (depth == 0)
                break;
            else
                --depth;
        }
        else if (str[i] == start)
            ++depth;
    if (e > s)
        return str.Substring(s + 1, e - s - 1);
    return null;
}

我最近一直在使用和滥用c# 9，甚至在一些可疑的场景中，我也忍不住要加入span…只是为了好玩，以下是上述答案的变体:

var input = "User name (sales)";
var txtSpan = input.AsSpan();
var startPoint = txtSpan.IndexOf('(') + 1;
var length = txtSpan.LastIndexOf(')') - startPoint;
var output = txtSpan.Slice(startPoint, length);

对于OP的特定场景，它产生正确的输出。 (就我个人而言，我会使用其他人发布的RegEx。在上述解决方案崩溃的情况下，更容易解决更棘手的情况)。

我为自己的项目做了一个更好的版本(作为扩展方法):

//Note: This only captures the first occurrence, but 
//can be easily modified to scan across the text (I'd prefer Slicing a Span)  
public static string ExtractFromBetweenChars(this string txt, char openChar, char closeChar)
{
    ReadOnlySpan<char> span = txt.AsSpan();
    int firstCharPos = span.IndexOf(openChar);
    int lastCharPos = -1;

    if (firstCharPos != -1) 
    { 
        for (int n = firstCharPos + 1; n < span.Length; n++)
        {
            if (span[n] == openChar) firstCharPos = n; //This allows the opening char position to change
            if (span[n] == closeChar) lastCharPos = n;
            if (lastCharPos > firstCharPos) break;
            //This would correctly extract "sales" from this [contrived]
            //example: "just (a (name (sales) )))(test"
        }
        return span.Slice(firstCharPos + 1, lastCharPos - firstCharPos - 1).ToString();
    }
    return "";
}

我在寻找一个非常相似的实现的解决方案时遇到了这个问题。

下面是我的实际代码片段。从第一个字符(索引0)开始子字符串。

 string separator = "\n";     //line terminator

 string output;
 string input= "HowAreYou?\nLets go there!";

 output = input.Substring(0, input.IndexOf(separator)); 

使用这个函数:

public string GetSubstringByString(string a, string b, string c)
{
    return c.Substring((c.IndexOf(a) + a.Length), (c.IndexOf(b) - c.IndexOf(a) - a.Length));
}

用法如下:

GetSubstringByString("(", ")", "User name (sales)")

输出将是:

sales

一个非常简单的方法是使用正则表达式:

Regex.Match("User name (sales)", @"\(([^)]*)\)").Groups[1].Value

作为对(非常有趣的)评论的回应，这里是同一个正则表达式的一些解释:

\(             # Escaped parenthesis, means "starts with a '(' character"
    (          # Parentheses in a regex mean "put (capture) the stuff 
               #     in between into the Groups array" 
       [^)]    # Any character that is not a ')' character
       *       # Zero or more occurrences of the aforementioned "non ')' char"
    )          # Close the capturing group
\)             # "Ends with a ')' character"

正则表达式可能是这里最好的工具。如果你不熟悉它们，我建议你安装Expresso -一个很棒的小正则表达式工具。

喜欢的东西:

Regex regex = new Regex("\\((?<TextInsideBrackets>\\w+)\\)");
string incomingValue = "Username (sales)";
string insideBrackets = null;
Match match = regex.Match(incomingValue);
if(match.Success)
{
    insideBrackets = match.Groups["TextInsideBrackets"].Value;
}