Regular expression that recognises 3.1 and 3. as well as .1 as double

Asked May 31 '17 at 20:01

Active May 31 '17 at 20:01

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What is the right regular expression to identify a floating point number such that only the decimal point and one number is required.

re = QRegExp("[-+]?[0-9]*\\.[0-9]+");
if (re.exactMatch(s))
    std::cout<< "Double"<<std::endl;

This code identifies 3.1 and .1 as double but not 3.. The trouble is, that if I make the second number block optional (replacing + with a *) then . would also be a double. How can I fix that?

I use Qts regular expression library, but I guess std::regex would work the same.

asked May 31 '17 at 20:01

dani

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See https://regex101.com/r/6y0dn5/1 – Wiktor Stribiżew May 31 '17 at 20:05
@WiktorStribizew that would also catch integers which shouldn't be: 3 is not a double (although not stated in my question) – dani May 31 '17 at 20:16
Trying to solve a problem using regular expression just means that you now have two problems – Support Ukraine May 31 '17 at 20:19
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It is even easier then, remove the optional group - https://regex101.com/r/bcU1fT/1 – Wiktor Stribiżew May 31 '17 at 20:20

Regular expression that recognises 3.1 and 3. as well as .1 as double

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