Why is `\d` Slower Than `[0-9]` in C# Regex?

C#regular expression

Slower than slower d [0-9] This article discusses a surprising discovery in the C#regular expression engine:

character type seems to be lower than the

character range efficiency, even if d is a super set of [0-9]. [0-9] d The difference between

and

d [0-9] The main reason for the difference in efficiency is the difference between these two characters:

:

match any unicode number character. This includes not only standard numbers 0-9, but also other numbers used in different languages ​​and writing systems. For example, Persian numbers and Devanagari numbers are also
• . d : d Only match the number 0-9. It is a compact representation of the character set .
• The impact on performance [0-9] [0123456789] When matching the string with the regular expression, the regular expression engine needs to compare each character in the string with the specified character class. For , it must perform additional inspections to determine whether the character is a unicode number, which may be higher than the simple checking character in the range of 0-9.

Test verification

The test code provided by demonstrates this performance difference. On the more than 10,000 random string (each string contains about 50%of the numbers), the following results are obtained:

d regular expression

: 00: 00: 00.2141226 (slower)

Regular expression : 00: 00: 00.1357972 (Fast)

Regular expression

: 00: 00: 00.1388997 (slightly slower than

)
• d
Conclusion
• [0-9]
Although is a convenient abbreviation of
• , it is not always the best choice in terms of performance. If you only need to match the standard number 0-9, it is recommended to use the [0123456789] character range. [0-9]

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