简单的电话号码正则表达式以匹配数字，空格等

Question

I'm trying to modify a fairly basic regex pattern in C# that tests for phone numbers.

The patterns is -

[0-9]+(\.[0-9][0-9]?)?

I have two questions -

1) The existing expression does work (although it is fairly restrictive) but I can't quite understand how it works. Regexps for similar issues seem to look more like this one -

/^[0-9()]+$/

2) How could I extend this pattern to allow brackets, periods and a single space to separate numbers. I tried a few variations to include -

[0-9().+\s?](\.[0-9][0-9]?)?

Although i can't seem to create a valid pattern.

Any help would be much appreciated.

Thanks,

Answer 1

The + after the character set is a quantifier (meaning the preceeding character, character set or group is repeated) at least one, and unlimited number of times and it's greedy (matched the most possible).

Then [0-9().+\\s]+ will match any character in set one or more times.

Answer 2

[0-9]+(\.[0-9][0-9]?)?

First of all, I recommend checking out either regexr.com or regex101.com, so you yourself get an understanding of how regex works. Both websites will give you a step-by-step explanation of what each symbol in the regex does.

Now, one of the main things you have to understand is that regex has special characters . This includes, among others, the following: []().-+*?\\^$ . So, if you want your regex to match a literal . , for example, you would have to escape it, since it's a special character. To do so, either use \\. or [.] . Backslashes serve to escape other characters, while [] means "match any one of the characters in this set". Some special characters don't have a special meaning inside these brackets and don't require escaping.

Therefore, the regex above will match any combination of digits of length 1 or more, followed by an optional suffix (foobar)? , which has to be a dot, followed by one or two digits. In fact, this regex seems more like it's supposed to match decimal numbers with up to two digits behind the dot - not phone numbers.

/^[0-9()]+$/

What this does is pretty simple - match any combination of digits or round brackets that has the length 1 or greater.

[0-9().+\s?](\.[0-9][0-9]?)?

What you're matching here is:

• one of: a digit, round bracket, dot, plus sign, whitespace or question mark; but exactly once only!
• optionally followed by a dot and one or two digits

A suitable regex for your purpose could be:

(\+\d{2})?((\(0\)\d{2,3})|\d{2,3})?\d+

Enter this in one of the websites mentioned above to understand how it works. I modified it a little to also allow, for example +49 123 4567890. Also, for simplicity, I didn't include spaces - so when using this regex, you have to remove all the spaces in your input first. In C#, that should be possible with yourString.Replace(" ", ""); (simply replacing all spaces with nothing = deleting spaces)