CODEWITHSUNDEEP
c#regexsubstring
xtmq
xtmq

Reputation: 3693

Regex matching string that doesn't contains substring

I try to find string that doesn't contains the same substring. This is my code: 

var regex = new Regex(@"aaa(?!.*aaa).*aaa");
var str1 = @"aaa aaa aaa";
var match = regex.Match(str1); // no
var str1 = @"aaa bbb aaa";
var match = regex.Match(str1); // yes

But this code doesn't work... What I do wrong?

Thanks!

Upvotes: 0

Views: 4051

Answers (2)

Sam Greenhalgh
Sam Greenhalgh

Reputation: 6136

Im going to take a stab in the dark here and guess that you're trying to do this.

i.e. 

`\b(\w+)\s+(?!\1\b)`

Matches a word \b(\w+) Followed by whitespace \s+ Followed by a negative look-ahead for a back reference to the previously matched word. (?!\1\b)

[Test]
public void RegexTest()
{
    var regex = new Regex(@"\b(\w+)\s+(?!\1\b)");
    var str1 = @"aaa aaa aaa";
    Assert.IsFalse(regex.IsMatch(str1)); // no
    var str2 = @"aaa bbb aaa";
    Assert.IsTrue(regex.IsMatch(str2)); // yes
}

Upvotes: 0

Qtax
Qtax

Reputation: 33908

You want an expression like this:

aaa(?:(?!aaa).)*aaa

(?:(?!aaa).)* matches strings that do not contain aaa (in whole or part).

You could also write it like this:

aaa(?:[^a]+|a(?!aa))*aaa

Upvotes: 7

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