Question

What s the shortest regex that can match non-zero floating point numbers with any number of decimal places?

It should accept numbers like

-1
-5.9652
-7.00002
-0.8
-0.0500
-0.58000
0.01
0.000005
0.9900
5
7.5
7.005

but reject constructions such as

.
.02
-.
-.996
0
-0
0.
-0.
-0.000
0.00
--
..
+
+0
+1
+.
+1.26
,etc

I do not need support for the scientific notation, with e , E and such.
The language I m using is C#, by the way.

Answer 1

^-?(0.d*[1-9]|[1-9]d*(.d+)?)$

EDIT Updated to reflect new requirements (last decimals can be zero)

^-?(0.d*[1-9]d*|[1-9]d*(.d+)?)$

(Shorter than using lookahead: ^-?(0.(?=[1-9])d*|[1-9]d*(.d+)?)$.)

EDIT2 If e.g. 001.000 can pass

^-?(?=.*[1-9])d+(.d+)?$

Answer 2

This is the one I always use:

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

Utilized in a PHP example:

<?php

$s=  1.234e4 ;

preg_match( ~(+|-)?([0-9]+.?[0-9]*|.[0-9]+)([eE](+|-)?[0-9]+)?~ , $s, $m);
print_r($m);

?>

Output:

Array
(
    [0] => 1.234e4
    [1] =>
    [2] => 1.234
    [3] => e4
)

Answer 3

-?(?!0)d+(.d+)?

Note: Remember to put ^ $ if it s not done by your regexp matcher.

May I ask why the "shortest"? A pre-compiler RegExp or the same with non-matching groups could be faster. Also a test for zero could possibly be faster too.

Answer 4

You might wish to consider these variations.

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