Regular expression for precise numerical values of a specific magnitude (any programming language)

Question

Regular expression for precise numerical values of a specific magnitude (any programming language)

I have been searching for a solution to what I thought was a common problem but haven't found one yet.

What I need is a regular expression that will fail on a specific number of significant figures (a Max), but pass for fewer than the Max. It should also work with both dot or comma (French) decimal separators.

For 15 significant figures, the following values should pass:
0
0.00
1
-1
1.23456789012345
10.2345678901234
12.3456789012345
-123.4
-12.34
-1,33
-1.33
-123456789012345
-1234567890123450
-12345678901234.50
12345678901234.50
123456789012345.00

// These values should fail:
-1234567890123456
-12345678901234.56
12345678901234.56
123456789012345.60
1.234567890123456
12.34567890123456
123456789012340.6
123456789012300.67
123456789012300000000000.67
10000000000010000000001000010000000001.22

I understand that I need to use negative lookaheads and have come close with this so far:

^(?!(?:.*?[1-9]){15,})([-+]?\s*\d+[\.\,]?\d*?)$

https://regex101.com/r/hQ1rP0/218

However, as you can see, the last few still pass. Any suggestions?

javascript regex regex-lookarounds

Answer 1

Answer №1

Code

If you are looking for actual scientific notation, where leading zeros matter before the decimal symbol, here is the regex pattern to use:

^-?(?=\d{1,15}(?:[.,]0+)?$|(?:(?=.{1,16}0*$)(?:\d+[.,]\d+)))‌.+$

However, if you need a regex that works for cases with leading zeros regardless of decimal position, this alternative will work:

You can see this regex in action here

^-?(?=\d{1,15}(?:[.,]0+)?0*$|(?:(?=.{1,16}0*$)(?:\d+[.,]\d+)‌)).+$

Explanation

^ This asserts the position at the start of the line
-? Match zero or one hyphen character literally
```
(?=\d{1,15}(?:[.,]0+)?0*$|(?:(?=.{1,16}0*$)(?:\d+[.,]\d+)))
```
Positive lookahead ensuring what follows matches the following
- \d{1,15}(?:[.,]0+)?0*$ Option 1
  - \d{1,15} Matches between 1 and 15 of any digit character
  - (?:[.,]0+)? Matches a decimal symbol ,. followed by one or more 0s literally, but either zero or one time
  - 0* Matches any number of 0s literally
  - $ Asserts the position at the end of the line
- (?:(?=.{1,16}0*$)(?:\d+[.,]\d+)) Option 2
  - (?=.{1,16}0*$) Ensures what follows matches the following
  - .{1,16} Matches any character between 1 and 16 times
  - 0* Matches any number of 0s literally
  - $ Asserts the position at the end of the line
  - (?:\d+[.,]\d+) Matches the following
  - \d+ Matches any digit between 1 and unlimited times
  - [,.] Matches a decimal character
  - \d+ Matches a digit between 1 and unlimited times
.+ Matches any character one or more times
$ Asserts the position at the end of the line (not essential but helps with readability)

Answer 2

Code

If you are looking for actual scientific notation, where leading zeros matter before the decimal symbol, here is the regex pattern to use:

^-?(?=\d{1,15}(?:[.,]0+)?$|(?:(?=.{1,16}0*$)(?:\d+[.,]\d+)))‌.+$

However, if you need a regex that works for cases with leading zeros regardless of decimal position, this alternative will work:

You can see this regex in action here

^-?(?=\d{1,15}(?:[.,]0+)?0*$|(?:(?=.{1,16}0*$)(?:\d+[.,]\d+)‌)).+$

Explanation

^ This asserts the position at the start of the line
-? Match zero or one hyphen character literally
```
(?=\d{1,15}(?:[.,]0+)?0*$|(?:(?=.{1,16}0*$)(?:\d+[.,]\d+)))
```
Positive lookahead ensuring what follows matches the following
- \d{1,15}(?:[.,]0+)?0*$ Option 1
  - \d{1,15} Matches between 1 and 15 of any digit character
  - (?:[.,]0+)? Matches a decimal symbol ,. followed by one or more 0s literally, but either zero or one time
  - 0* Matches any number of 0s literally
  - $ Asserts the position at the end of the line
- (?:(?=.{1,16}0*$)(?:\d+[.,]\d+)) Option 2
  - (?=.{1,16}0*$) Ensures what follows matches the following
  - .{1,16} Matches any character between 1 and 16 times
  - 0* Matches any number of 0s literally
  - $ Asserts the position at the end of the line
  - (?:\d+[.,]\d+) Matches the following
  - \d+ Matches any digit between 1 and unlimited times
  - [,.] Matches a decimal character
  - \d+ Matches a digit between 1 and unlimited times
.+ Matches any character one or more times
$ Asserts the position at the end of the line (not essential but helps with readability)

Regular expression for precise numerical values of a specific magnitude (any programming language)

Answer №1

Code

Explanation

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