正则表达式量词中的反向引用 [英] Backreference in Regular Expression Quantifier

问题描述

我有一个字符串，其中包含一个长度为以下字段的标题.

I have a string that contains a header with a length of the following field.

示例:

fillerfillerCA20 abcdefghijklmnopqrst CA5 zyxwvfillerfiller

我需要找到两个值:abcdefghijklmnopqrst和zyxwv

I need to find the two values: abcdefghijklmnopqrst and zyxwv

我打算使用反向引用来获取量词的长度:

I was going to use a backreference to get the length for the quantifier:

(?i)ca(?<length>\d+?)\x20.{\k<length>}\x20?

但显然，不支持在量词中使用反向引用.

but apparently, using a backreference in a quantifier is not supported.

我怎样才能做到这一点?

How can I accomplish this?

推荐答案

不是一步到位.正则表达式不能是自引用的.它们首先被构建，然后被使用.一旦构建了正则表达式，就无法重新构建/扩充.

Not in one step. Regular expressions cannot be self-referential. They are first built, and then used. No re-building/augmenting is possible once the regex is built.

您可以像之前一样匹配长度信息，并在第二步中使用它，同时评估匹配.

You can match the length info as you already do and use it in a second step, while evaluating the matches.

先发制人的评论:我知道可以用 "(.)\1" 来匹配同一个字符两次.不过，这不是我所说的自我参照".

Preemptive comment: I know that one can do "(.)\1" to match the same character twice. This is not what I mean with "self-referential", though.

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