C# third index of a character in a string

Question

is there a command that can get the third index of a character in a string? For example:

error: file.ext: line 10: invalid command [test:)]

In the above sentence, I want to the index of the 3rd colon, the one next to the 10. How could I do that? I know of string.IndexOf and string.LastIndexOf, but in this case I want to get the index of a character when it is used the third time.

Answer 1

String.IndexOf will get you the index of the first, but has overloads giving a starting point. So you can use a the result of the first IndexOf plus one as the starting point for the next. And then just accumulate indexes a sufficient number of times:

var offset = myString.IndexOf(':');
offset = myString.IndexOf(':', offset+1);
var result = myString.IndexOf(':', offset+1);

Add error handling unless you know that myString contains at least three colons.

Answer 2

You could write something like:

    public static int CustomIndexOf(this string source, char toFind, int position)
    {
        int index = -1;
        for (int i = 0; i < position; i++)
        {
            index = source.IndexOf(toFind, index + 1);

            if (index == -1)
                break;
        }

        return index;
    }

EDIT: Obviously you have to use it as follows:

int colonPosition = myString.CustomIndexOf(',', 3);