Question

I have a problem to define a regexp that matches floating point numbers but do NOT identify integers.

I have the following regular expression, which matches floating numbers.

(\+|-)?([0-9]+\.?[0-9]*|\.[0-9]+)([eE](\+|-)?[0-9]+)?

How can I modify the expression above so that it doesn’t match integers?

Here is a example of what should be matched:

3.3
.3
5E6
.2e-14
7E+3
4.
5.E2
1e2

Answer 1

If your regex flavor supports lookaheads, require one of the floating-point characters before the end of the number:

((\+|-)?(?=\d*[.eE])([0-9]+\.?[0-9]*|\.[0-9]+)([eE](\+|-)?[0-9]+)?

Additional reading.

Here is also a slightly optimized version:

[+-]?(?=\d*[.eE])(?=\.?\d)\d*\.?\d*(?:[eE][+-]?\d+)?

We start with an optional + or -. Then we require one of the characters ., e or E after an arbitrary amount of digits. Then we also require at least one digit, either before or after the string. The we just match digits, an optional . and more digits. Then (completely optional) an e or an E and optional + or - and then one or more digits.