c# - 如何进行平衡组捕获？

Question

假设我有这个文本输入。

 tes{}tR{R{abc}aD{mnoR{xyz}}}

我想提取 ff 输出:

 R{abc}
 R{xyz}
 D{mnoR{xyz}}
 R{R{abc}aD{mnoR{xyz}}}

目前，我只能使用 msdn 中的平衡组方法提取{}组内的内容.这是模式:

 ^[^{}]*(((?'Open'{)[^{}]*)+((?'Target-Open'})[^{}]*)+)*(?(Open)(?!))$

有谁知道如何在输出中包含 R{} 和 D{}？

Answer 1

我认为这里需要一种不同的方法。一旦匹配到第一个较大的组 R{R{abc}aD{mnoR{xyz}}}(请参阅我对可能的拼写错误的评论)，您将无法将子组放入其中正则表达式不允许您捕获单个 R{ ... } 组。

因此，必须有某种方法来捕获而不是消耗，而做到这一点的明显方法是使用积极的前瞻。从那里，您可以使用您使用的表达式，尽管有一些变化以适应焦点的新变化，我想出了:

(?=([A-Z](?:(?:(?'O'{)[^{}]*)+(?:(?'-O'})[^{}]*?)+)+(?(O)(?!))))

[我还将“Open”重命名为“O”并删除了右括号的命名捕获以使其更短并避免匹配中的噪音]

在 regexhero.net(目前我知道的唯一免费的 .NET 正则表达式测试器)上，我得到了以下捕获组:

1: R{R{abc}aD{mnoR{xyz}}}
1: R{abc}
1: D{mnoR{xyz}}
1: R{xyz}

正则表达式分解:

(?=                         # Opening positive lookahead
    ([A-Z]                  # Opening capture group and any uppercase letter (to match R & D)
        (?:                 # First non-capture group opening
            (?:             # Second non-capture group opening
                (?'O'{)     # Get the named opening brace
                [^{}]*      # Any non-brace
            )+              # Close of second non-capture group and repeat over as many times as necessary
            (?:             # Third non-capture group opening
                (?'-O'})    # Removal of named opening brace when encountered
                [^{}]*?     # Any other non-brace characters in case there are more nested braces
            )+              # Close of third non-capture group and repeat over as many times as necessary
        )+                  # Close of first non-capture group and repeat as many times as necessary for multiple side by side nested braces
        (?(O)(?!))          # Condition to prevent unbalanced braces
    )                       # Close capture group
)                           # Close positive lookahead

---

以下在 C# 中无效

我实际上想尝试一下它应该如何在 PCRE 引擎上运行，因为可以选择递归正则表达式，而且我认为它更容易，因为我更熟悉它并且产生了更短的正则表达式: )

(?=([A-Z]{(?:[^{}]|(?1))+}))

regex101 demo

(?=                    # Opening positive lookahead
    ([A-Z]             # Opening capture group and any uppercase letter (to match R & D)
        {              # Opening brace
            (?:        # Opening non-capture group
                [^{}]  # Matches non braces
            |          # OR
                (?1)   # Recurse first capture group
            )+         # Close non-capture group and repeat as many times as necessary
        }              # Closing brace
    )                  # Close of capture group
)                      # Close of positive lookahead