How to match string by using regular expression which will not allow same special character at same-CodePudding

I m trying to matching a string which will not allow same special character at same time

my regular expression is:

 [RegularExpression(@"^ [a-zA-Z0-9] [a-zA-Z0-9.&' '-] [a-zA-Z0-9]$")]

this solve my all requirement except the below two issues

this is my string : bracks

acceptable :

bra-cks, b-r-a-c-ks, b.r.a.c.ks,  bra cks (by the way above regular expression solved this)

not acceptable:

issue 1: b.. or bra..cks, b..racks, bra...cks (two or more any special character together),  
issue 2: bra    cks (two ore more white space together)

CodePudding user response：

To match a string using a regular expression that does not allow the same special character to appear more than once at a time, you can use a negative lookahead assertion. A negative lookahead assertion is a pattern that matches a string only if it is not followed by a certain pattern.

^(?!.*(.)\1)[^A-Za-z0-9]*$

CodePudding user response：

I don`t know why you need to use regex, but you can try to check if there are two special chars in a row using Linq.

Example with two dots in a row.

string s = "s.t.r.i..n.g";
     
bool hasTwoDotsInARow = s.ToCharArray()
   .Select((c, i) => new { c, i })
   .Any(x => x.c == '.' && x.i > 0 && s[x.i - 1] == '.');

Console.WriteLine(hasTwoDotsInARow);