C# 使用正则表达式从字符串中提取子字符串
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Extract substring from string with Regex
提问by Nelson Reis
Imagine that users are inserting strings in several computers.
想象一下，用户在多台计算机中插入字符串。
On one computer, the pattern in the configuration will extract some characters of that string, lets say position 4 to 5. On another computer, the extract pattern will return other characters, for instance, last 3 positions of the string.
在一台计算机上，配置中的模式将提取该字符串的一些字符，比如说位置 4 到 5。在另一台计算机上，提取模式将返回其他字符，例如，字符串的最后 3 个位置。
These configurations (the Regex patterns) are different for each computer, and should be available for change by the administrator, without having to change the source code.
这些配置（Regex 模式）对于每台计算机都是不同的，管理员应该可以更改，而无需更改源代码。
Some examples:
一些例子：
Original_String Return_Value
User1 - abcd78defg123 78
User2 - abcd78defg123 78g1
User3 - mm127788abcd 12
User4 - 123456pp12asd ppsd
Can it be done with Regex? Thanks.
可以用正则表达式完成吗？谢谢。
采纳答案by Greg Domjan
To have a regex capture values for further use you typically use (), depending on the regex compiler it might be () or for microsoft MSVC I think it's []
要获得正则表达式捕获值以供进一步使用，您通常使用 ()，具体取决于正则表达式编译器，它可能是 () 或对于 microsoft MSVC 我认为它是 []
Example
例子
User4 - 123456pp12asd ppsd
is most interesting in that you have here 2 seperate capture areas. Is there some default rule on how to join them together, or would you then want to be able to specify how to make the result?
最有趣的是这里有 2 个单独的捕获区域。是否有一些关于如何将它们连接在一起的默认规则，或者您是否希望能够指定如何生成结果？
Perhaps something like
也许像
r/......(..)...(..)// for ppsd
r/......(..)...(..)/-/ for sd-pp
do you want to run a regex to get the captures and handle them yourself, or do you want to run more advanced manipulation commands?
您是要运行正则表达式来获取捕获并自己处理它们，还是要运行更高级的操作命令？
回答by Marc Gravell
Why do you want to use regex for this? What is wrong with:
为什么要为此使用正则表达式？出什么问题了：
string foo = s.Substring(4,2);
string bar = s.Substring(s.Length-3,3);
(you can wrap those up to do a bit of bounds-checking on the length easily enough)
（你可以把它们包起来，很容易地对长度进行一些边界检查）
If you really want, you could wrap it up in a Func<string,string>to put somewhere - not sure I'd bother, though:
如果你真的想要，你可以把它包起来Func<string,string>放在某个地方 - 不过我不确定我会打扰：
Func<string, string> get4and5 = s => s.Substring(4, 2);
Func<string,string> getLast3 = s => s.Substring(s.Length - 3, 3);
string value = "abcd78defg123";
string foo = getLast3(value);
string bar = get4and5(value);
回答by kgrad
I'm not sure what you are hoping to get by using RegEx. RegEx is used for pattern matching. If you want to extract based on position, just use substring.
我不确定您希望通过使用 RegEx 获得什么。RegEx 用于模式匹配。如果要根据位置提取，只需使用子字符串。
回答by Noldorin
It seems to me that Regex really isn't the solution here. To return a section of a string beginning at position pos(starting at 0) and of length length, you simply call the Substring function as such:
在我看来，Regex 真的不是这里的解决方案。要返回从位置pos（从 0 开始）和长度为length的字符串的一部分，您只需像这样调用 Substring 函数：
string section = str.Substring(pos, length)
回答by annakata
Grouping. You could match on /^.{3}(.{2})/ and then look at group $1 for example.
分组。例如，您可以匹配 /^.{3}(.{2})/ 然后查看组 $1。
The question is why? Normal string handling i.e. actual substring methods are going to be faster and clearer in intent.
问题是为什么？正常的字符串处理，即实际的子字符串方法在意图上会更快更清晰。
回答by Gumbo
If you really want to use regex:
如果你真的想使用正则表达式：
^...(..)
And:
和：
.*(...)$
