Get Second to last character position from string

Question

I have a dynamically formed string like - part1.abc.part2.abc.part3.abc

In this string I want to know position of second to last \".\" so that i can split string as

Answer 1

This would be the solution, with the best possible performance (it probably won't get much faster and memory lightweight than this, unless you want to go the unsafe route):

public static int LastIndexOf(this string str, char charToSearch, int repeatCound)
{
    int index = -1;
    for(int i = str.Length - 1; i >= 0, numfound < repeatCound)
    {
        if(str[i] == charToSearch)
        {
            index = i; 
            numfound++;
        }
    }

    return index;
}

Answer 2

string str = "part1.abc.part2.abc.part3.abc";
int ix1 = str.LastIndexOf('.');
int ix2 = ix1 > 0 ? str.LastIndexOf('.', ix1 - 1) : -1;

There are always lovers of Regexes (and jQuery), so I'll give a Regex solution (for the jQuery solution you'll have to wait :-) ):

var match = Regex.Match(str, @"\.[^\.]*\.", RegexOptions.RightToLeft);
int ix = match.Success ? match.Index : -1;

(note that I'm an hater of Regexes, I'm giving it to you so that you can have enough rope to hang yourself if you so choose).

Be aware that I'm using the RegexOptions.RightToLeft option so that the Regex starts at the last character.

Answer 3

Here is another solution:

         string aString = "part1.abc.part2.abc.part3.abc";
        // Getting string until last dot
        var untilLastDot = aString.Substring(0, aString.LastIndexOf("."));
        // Now we have string until last dot and last dot here will be last but one 
        // and getting text from last but one dot to end
        string lastWordButOne = aString.Substring(untilLastDot.LastIndexOf(".") + 1);
        // Result: part3.abc

hope helps, Thanks!

Answer 4

LastIndexOf should do what you want. Just do it twice.