What does [++]*+ stand for in regexp

Question

I'm using libphonenumber and I try to check some phone numbers if they are valid with regexp pattern VALID_PHONE_NUMBER which can be found here and it looks like this

private static final String VALID_PHONE_NUMBER =
      DIGITS + "{" + MIN_LENGTH_FOR_NSN + "}" + "|" +
      "[" + PLUS_CHARS + "]*+(?:[" + VALID_PUNCTUATION + STAR_SIGN + HASH_SIGN +"]*" + DIGITS + "){3,}[" +
      VALID_PUNCTUATION + STAR_SIGN + HASH_SIGN + VALID_ALPHA + DIGITS + "]*";

On my Android phone this expression is compiled to following

\p{Nd}{1}|[++]*+(?:[-x--?-?--/  ?? ()()[].\[\]/~?~~*#]*\p{Nd}){3,}[-x--?-?--/  ?? ()()[].\[\]/~?~~*#DEFGABCLMNOHIJKUTWVQPSRYXZdefgabclmnohijkutwvqpsryxz\p{Nd}]*

What does it mean [++]*+

Does it mean "plus-or-plus zero-or-more-times and then plus?

Does it make any sense to have two pluses next to each other?

I checked the regex at the link you gave and there is no `[++]*+` but there is `[+]*+` which is a possessive quantifier since you are using Java. — Ibrahim Najjar, Aug 14 '13 at 13:48
well I see static final String PLUS_CHARS = "+\uFF0B"; and I belive that it's ++ — Marian Paździoch, Aug 14 '13 at 14:15

score 3 · Accepted Answer · answered Aug 14 '13 at 13:42

3

[++] matches a + or a +

*+ matches the [++] zero or more times, possessively

See: http://www.regular-expressions.info/possessive.html

answered Aug 14 '13 at 13:42

Bart Kiers

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score 2 · Answer 2 · edited May 23 '17 at 12:28

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The rightmost + is fairly new. As others have said, [++] means "find a single +". with the * quantifier: [++]* means "zero or more plus signs".

The extra rightmost + in [++]*+ is not supported by all Regular Expression engines, but means "do not do any backtracking", i.e. do a "maximum match". Contrast with ?, which does a minimum match.

See also this question

edited May 23 '17 at 12:28

Community

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answered Aug 14 '13 at 13:42

cdarke

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score 2 · Answer 3 · answered Aug 14 '13 at 13:43

2

+ within character class is treated as a literal..It should be [+]*+

*+ is Possessive Quantifier..It doesn't backtrack..

answered Aug 14 '13 at 13:43

Anirudha

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SLaks · Answer 4 · 2013-08-14T13:44:30.117

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Yes
No

A character class ([...]) ignores duplicate characters.
Therefore, [++] is equivalent to \+.

edited Aug 14 '13 at 13:44

answered Aug 14 '13 at 13:36

SLaks

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I think the final `+` is a possessive quantifier. – johnchen902 Aug 14 '13 at 13:40
In most popular regex implemetations, the `+` in `*+` denotes `*` is possessive: http://www.regular-expressions.info/possessive.html – Bart Kiers Aug 14 '13 at 13:41

Ravi K Thapliyal · Answer 5 · 2013-08-14T13:45:23.583

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The second + is redundant both inside and outside the character class.

Within the character class [++] it's just ignored. Outside the character class it acts as a quantifier (one or more) ~~but isn't valid because~~ except when preceded with another quantifier like * here (for zero or more) as then it denotes possessiveness.

More info at Possessive Quantifiers

You can make a quantifier possessive by placing an extra + after it. E.g. * is greedy, *? is lazy, and *+ is possessive. ++, ?+ and {n,m}+ are all possessive as well.

edited Aug 14 '13 at 13:45

answered Aug 14 '13 at 13:40

Ravi K Thapliyal

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I think the final `+` is a possessive quantifier. – johnchen902 Aug 14 '13 at 13:41

What does [++]*+ stand for in regexp

5 Answers5