What is simpliest way to get Line number from char position in String?

Question

What is simpliest way to get Line number from char position in String in C#? (or get Position of line (first char in line) ) Is there any built-in function ? If there are n

Answer 1

A slight variation on Jan's suggestion, without creating a new string:

var lineNumber = input.Take(pos).Count(c => c == '\n') + 1;

Using Take limits the size of the input without having to copy the string data.

You should consider what you want the result to be if the given character is a line feed, by the way... as well as whether you want to handle "foo\rbar\rbaz" as three lines.

EDIT: To answer the new second part of the question, you could do something like:

var pos = input.Select((value, index) => new { value, index })
               .Where(pair => pair.value == '\n')
               .Select(pair => pair.index + 1)
               .Take(line - 1)
               .DefaultIfEmpty(1) // Handle line = 1
               .Last();

I think that will work... but I'm not sure I wouldn't just write out a non-LINQ approach...