Question

I write simple application in C++/Qt. And i have a text and some octal number in it. My app splits this text by spaces. And i need to check octal numbers from text. How can i select octal numbers from this text with regular expressions?

Thank you.

Answer 1

You can use the following regex to match only octal numbers:

^0[1-7][0-7]*$

• ^,$: Anchors
• 0: A literal 0. All octal numbers
  begin with a 0.
• [1-7]: Char class for digits from 1
  to 7 as only these are valid octal
  digits.
• * : Quantifier for zero or more of the previous thing.

So basically this regex matches only those strings that have a 0 in the beginning and contain one or more digits from 1 to 7.

If the leading 0 requirement is not there you can use the regex:

^[1-7][0-7]*$