[英]Backreference in Regular Expression Quantifier
I have a string that contains a header with a length of the following field. 我有一个包含标题的字符串,该标题的长度为以下字段。
Example: 例:
fillerfillerCA20 abcdefghijklmnopqrst CA5 zyxwvfillerfiller
I need to find the two values: abcdefghijklmnopqrst and zyxwv 我需要找到两个值:abcdefghijklmnopqrst和zyxwv
I was going to use a backreference to get the length for the quantifier: 我将使用后向引用来获取量词的长度:
(?i)ca(?<length>\d+?)\x20.{\k<length>}\x20?
but apparently, using a backreference in a quantifier is not supported. 但显然,不支持在量词中使用向后引用。
How can I accomplish this? 我该怎么做?
Not in one step. 不是一步。 Regular expressions cannot be self-referential.
正则表达式不能是自引用的。 They are first built, and then used.
它们首先被构建,然后被使用。 No re-building/augmenting is possible once the regex is built.
一旦构建了正则表达式,就无法重新构建/增强。
You can match the length info as you already do and use it in a second step, while evaluating the matches. 您可以像以前一样匹配长度信息,并在评估匹配结果的第二步中使用它。
Preemptive comment: I know that one can do "(.)\\1"
to match the same character twice. 抢先评论:我知道一个人可以做
"(.)\\1"
来两次匹配相同的字符。 This is not what I mean with "self-referential", though. 但是,这并不是我所说的“自我参照”。
更好地构建解析器:查找CA
的位置,读取以下数字字符,然后读取数字值所描述的下一个x字符。
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