Understanding a regex expression

Question

This expression evaluates a string to see if every character is a digit. I don't understand the -?. I know that ? means once or no times, but I'm not sure what putting dash in front of it means.

-?\d+

Ivaylo Strandjev · Accepted Answer · 2013-01-31 14:18:45Z

7

This is needed because an integer may be negative in which case it will start with a minus (-). So what you do here is to check for sequence of 1 or more digits optionally preceded by a single minus.

answered Jan 31, 2013 at 14:18

Ivaylo Strandjev

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user879559 Over a year ago

Thank you very much. Still learning how to use regex I guess.

Stanley De Boer · Accepted Answer · 2013-01-31 14:19:33Z

6

It is not a special character. The dash is there to allow negative numbers.

answered Jan 31, 2013 at 14:19

Stanley De Boer

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