C# 正则表达式 - 在字符之前匹配模式
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Regex - Match a Pattern Before a Character
提问by bplus
I'm currently building a toy assembler in c# (going through The Elements Of Computing Systemsbook).
我目前正在用 c# 构建一个玩具汇编器（通过计算系统的元素书）。
I need to match a very simple pattern, I thought this would be a good time to learn some regex but I'm struggling!
我需要匹配一个非常简单的模式，我认为这是学习一些正则表达式的好时机，但我很挣扎！
In the following examples I'd just like to match the letters before the '='
在以下示例中，我只想匹配 '=' 之前的字母
M=A
M=A
D=M
D=M
MD=A
MD=A
A=D
A=D
AD=M
AD=M
AMD=A
AMD=A
I've come up with the following:
我想出了以下几点：
([A-Z]{1,3})=
However this also matches the '=' which I don't want.
但是，这也与我不想要的 '=' 匹配。
I also tried:
我也试过：
([A-Z^\=]{1,3})=
But I still have the same problem - it a matches the '=' sign as well.
但我仍然有同样的问题 - 它也匹配 '=' 符号。
I'm using this siteto test my regexes.
我正在使用这个站点来测试我的正则表达式。
Any help would be really appreciated. Thank you in advance.
任何帮助将非常感激。先感谢您。
采纳答案by RichieHindle
回答by Conspicuous Compiler
What you want is called a zero-width, lookahead assertion. You do:
你想要的是一个零宽度的前瞻断言。你做：
(Match this and capture)(?=before this)
In your case, this would be:
在您的情况下，这将是：
([A-Z^]{1,3})(?==)
回答by Nippysaurus
The following will group everything before the "=" and everything after.
下面将对“=”之前的所有内容和之后的所有内容进行分组。
([^=]*)=([^=]*)
it reads something like this:
它是这样写的：
match any amount of characters thats not a "=", followed by a "=", then any amount of characters thats not a "=".
匹配任何数量的不是“=”的字符，后跟一个“=”，然后是任何数量的不是“=”的字符。
回答by Dinah
You can also put the equals sign in a non-capturing parans with (?: ... )
您还可以使用 (?: ... ) 将等号放在非捕获参数中
([ADM]{1,3})(?:=)
It's been a bit since I did this chapter of the book but I think that since you need both parts of the expression anyway, I did a split on the = resulting in myArray[0] == M, myArray[1] == A
自从我完成本书的这一章以来已经有一段时间了，但我认为因为无论如何你都需要表达式的两个部分，所以我对 = 进行了拆分，导致 myArray[0] == M, myArray[1] == A
回答by Tola
I needed to match every character before the '=' so I came up with this
我需要匹配 '=' 之前的每个字符，所以我想出了这个
.*(?==)=
Matches every character before '=' but not "="
匹配 '=' 之前的每个字符，但不匹配“=”
