regex with only numbers in a string c++

I'm looking for a regex to find numbers in a string; if I have a string like:

li 12.12 si 43,23 45 31 uf 889 uf31 3.12345

I want to find only the numbers:

12.12 45 31 889 3.12345

I tried with the following pattern:

((\\+|-)?[[:digit:]]+)(\\.(([[:digit:]]+)?))?

but the output included uf31 and 43,23.

I tried with:

(?!([a-z]*((\\+|-)?[[:digit:]]+)(\\.(([[:digit:]]+)?))?[a-z]*))?((\\+|-)?[[:digit:]]+)(\\.(([[:digit:]]+)?))?

but this gave the same result.

What is the solution?

Thank you

SOLUTION leave to posterity the solution: - if you're looking for a simple and effective solution that does not use the regex, see Johnatan post below - if you're looking for a solution using RegEx, see wonderful regex from stribizhev

R"((?:^|\s)([+-]?[[:digit:]]+(?:\.[[:digit:]]+)?)(?=$|\s))"

Thanks !!!