Find Nth Occurence of character

[robertfah]

I've got a string in which I need to find the starting point of the 2nd underscore:

BBBB_BBBBB_20100101.doc

I am trying to extract BBBB_BBBBB from the file name. Is there a built in function that I can use that will search a string for the 2nd occurence of a character? Almost like IndexOf?

 

[jmeckley]

there is not a string.FindSecondIndexof(string) if that's what you're asking. building one wouldn't be difficult.

Jason Meckley
Programmer
Specialty Bakers, Inc.

faq855-7190
faq732-7259

 

[jges]

Will string.LastIndexOf() do what you want?

 

[jmeckley]

that would only work if there were exactly 2 underscores in the file name. if the file names follow the convention above it will work, other wise a string.IndexOf(string s, int occurance) will be required.

Jason Meckley
Programmer
Specialty Bakers, Inc.

faq855-7190
faq732-7259

 

[jges]

How about using a regular expression with a pattern of "^[a-zA-Z0-9]+_[a-zA-Z0-9]+_"? The match returned will have the 2nd underscore so you will have to trim that off, but should work.

 

[jmeckley]

nice. wrap that in an extension method to encapsulate the regex and you could have a nice little NthIndexOf method

pubic static class StringExtensions
{
   public static int NthIndexOf(this string s, int occurrence)
   {
      const string part = @"[a-zA-Z0-9]+_";
      var pattern = new StringBuilder("^");
      while(occurrence> 0)
      {
         pattern.Append(part);
         occurrence--;
      }
      var match = Regex.Match(pattern.ToString());
      return match.Success ? match.Index : -1;
   }
}

or something like that. you can then us it like this

var index = "hi_my_name_is_jason".NthIndexOf(2);
//index = 5

Jason Meckley
Programmer
Specialty Bakers, Inc.

faq855-7190
faq732-7259