What’s a Better Regex for Validating Floats?

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Asked By CuriousCoder92 On

I'm trying to improve my regex for identifying float numbers in a string. I currently have this regex: `^-?(d+.d*|d*.d+)$`, which works for inputs like `-90.`, `.67`, and `42.6`, but it fails to recognize just a decimal point `.` or a negative decimal `-.` as invalid. I'm looking for a regex that accommodates numbers that can have digits on either side of the decimal point while enforcing the rule that there must be at least one digit present. Any suggestions?

4 Answers

Answered By RegexMaster3000 On

Your regex isn't bad, but keep in mind that various programming languages interpret regex differently. There are many ways to construct a float-checking regex, and you might want to optimize for readability and maintainability.

PatternPal -

Good point! It can be tricky to ensure portability across platforms.

Answered By SmartCoder On

Just a reminder: it's worth noting that a float might start with a + sign or have an exponent like `+1.21E-6`. Additionally, numbers like `10` without a decimal are still considered valid floats in many languages, so keep that in consideration when forming your regex.

CuriousCoder92 -

Hmm, I'm not sure if I need to accommodate exponent formats for my project.

Answered By FloatChecker2021 On

Yours is probably the most readable one I've seen so far. You might also consider something like `^-?d*(d.|.d)d*$` for clarity and to satisfy more cases.

CuriousCoder92 -

Thanks for the suggestion! I find mine much easier to read too.

Answered By RegexFanatic87 On

Instead of getting too deep into regex, you might want to consider just converting the string to a float and handling exceptions. If it throws an error, then it’s not a valid float. Some languages also offer a method like TryParse() which is cleaner and provides a success flag plus the result. If you're preparing data for another system, matching its float rules is better, but otherwise, using built-in checks is usually sufficient.

TechieTom -

I love out-of-the-box thinking!

CodeNinja99 -

Exactly! It keeps things simple and efficient.

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