Split string after specific character or after max length

Question

i want to split a string the following way:

string s = "012345678x0123x01234567890123456789";
s.SplitString("x",10);

should be split into

012345678
x0123
x012345678
9012345678
9

eg the inputstring should be split after the character "x" or length 10 - what comes first.

here is what i've tried so far:

public static IEnumerable<string> SplitString(this string sInput, string search, int maxlength)
{
    int index = Math.Min(sInput.IndexOf(search), maxlength);
    int start = 0;
    while (index != -1)
    {
        yield return sInput.Substring(start, index-start);
        start = index;
        index = Math.Min(sInput.IndexOf(search,start), maxlength);
    }
}

Answer 1

I would go with this regular expression:

([^x]{1,10})|(x[^x]{1,9})

which means:

Match at most 10 characters that are not x OR match x followed by at most 9 characters thar are not x

Here is working example:

string regex = "([^x]{1,10})|(x[^x]{1,9})";
string input = "012345678x0123x01234567890123456789";
var results = Regex.Matches(input, regex)
                    .Cast<Match>()
                    .Select(m => m.Value);

which produces values by you.

Answer 2

Personally I don't like RegEx. It creates code that is hard to de-bug and is very hard to work out what it is meant to be doing when you first look at it. So for a more lengthy solution I would go with something like this.

    public static IEnumerable<string> SplitString(this string sInput, char search, int maxlength)
    {
        var result = new List<string>();
        var count = 0;
        var lastSplit = 0;

        foreach (char c in sInput)
        {
            if (c == search || count - lastSplit == maxlength)
            {
                result.Add(sInput.Substring(lastSplit, count - lastSplit));
                lastSplit = count;
            }

            count ++;
        }

        result.Add(sInput.Substring(lastSplit, count - lastSplit));

        return result;
    }

Note I changed the first parameter to a char (from a string). This code can probably be optimised some more, but it is nice and readable, which for me is more important.