在线等 正则表达式小问题

Question

本帖最后由 ceirel01 于 2010-12-05 23:28:27 编辑

Answer 1

1、提取正则：(?<=<div\s+class=\\"propDescValue_p\\">)(?:(?!</div>)[\s\S])+string pattern = "(?<=<div\\s+class=\\\\\"propDescValue_p\\\\\">)(?:(?!</div>)[\\s\\S])+";
2、可以过滤所有html标签，就是把"<xxx>"都替换成空字符串""。。

Answer 2

不知楼上是哪位朋友的马甲。
至少是阅读了过客兄博客很仔细的朋友。
稍微的一点建议，
因为是做捕获，环视效率并不高，并且class未必会是第一个attribute，不如直接写
<div[^>]+?class=\W*propDescValue_p\b[^>]*>([\s\S]+?)</div>
取分组1
string result = Regex.Match(html,@"<div[^>]+?class=\W*propDescValue_p\b[^>]*>[\s\S]+?</div>").Groups[1].Value;
(?!</div>)
的写法很好，第一次看到类似写法也是在过客兄博客上，这种写法只应当在很少的一些情况使用，例如他例子中的平衡组中，这样做效率不高，我做过测试，下面来说一下原因。
你每匹配一个字符，都被拆成2个部分，一个是后面不是</div>的一个“位置”，一个是实际匹配的字符，匹配一个字符，需要先环视，环视的结果是一个位置，得到这个位置后，再匹配位置后面的表达式[\s\S]。
这样效率不如.+?来的直接，.+?尽可能少匹配，当匹配后，尝试后面的表达式，后面如果是写</div，则非<的大多数情况只尝试一次匹配，发现失配后，回溯到.+?继续匹配下一个字符，直到完整的匹配到</div>才停止。.+?在这个情况下比较合理。
(ps: [\s\S]写的麻烦，我这里假定环境为单行模式了，.表示所有字符包含换行符 )

Answer 3

发完上面的回复，我想了想，不是很严谨，从字面上说(?:(?</div>)[\s\S].)+的写法，实际上和.+?</div>的匹配过程、顺序似乎是一致的，都是在下一次的匹配之前，先尝试</div>，当然，如果不是<的大多数字符，两者失配都应该是发生在第一个字符<的判断上，但效率的确差很远，做了一个简单测试字符串<div>$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F$GPGGA,031910.00,2308.3445,N,11320.1198,E,1,11,0.8,62.4,M,-6.5,M,,*4F</div>匹配结果一共用时：18637毫秒(18.637秒) [10000次]表达式1：<div>(?:(?!</div>)[\s\S])+</div>
执行时间：11536毫秒(11.536秒) 占总时间61.90%表达式2：<div>[\s\S]+?</div>
执行时间：7101毫秒(7.101秒) 占总时间38.10%
没实际看过.net正则引擎如何实现的，只是猜测，环视在匹配顺序上和非环视一致，但实现上，估计增加了开销。所以尽量少用环视，而是用全部匹配，通过分组返回结果。

Answer 4

楼上的楼上的楼上不是马甲。。过客兄博客昨晚才发现。。刚看了.NET正则第一个委托。。
用了环视是因为某某一天在论坛某某问题中看到某某大神既不包含xxx，又不包含xxx，也不包含xxx的做法现学现用，用的环视，之前一直用的非贪婪匹配。。
而且对于[\s\S]，之前一直用(?:.|\n)。。