从技术角度而言，正则表达式是表示某种模式的字符串(也就是说，由字母、数字和符号组成的字符序列)，用于定义零或更长的字符串。

Technically speaking, a regular expression is a string (that is, a sequence of characters composed of letters, Numbers, and symbols) that represents a pattern defining zero or more strings.

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放在表达式前表示被开方根的符号。

The root of a quantity as indicated by the radical sign .

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如果你在你的表达式中用到ul(表示无符号长整型)，那么你有了一个好的起点。

If you in your expression used UL (said unsigned long integer), then you have a good starting point.

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