How to read text file by particular line separator character?

Question

Reading a text file using streamreader.

using (StreamReader sr = new StreamReader(FileName, Encoding.Default))
{
     string line = sr.ReadLine();
}
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Answer 1

I needed a solution that reads until "\r\n", and does not stop at "\n". jp1980's solution worked, but was extremely slow on a large file. So, I converted Mike Sackton's solution to read until a specified string is found.

public static string ReadLine(this StreamReader sr, string lineDelimiter)
    {
        StringBuilder line = new StringBuilder();
        var matchIndex = 0;

        while (sr.Peek() > 0)
        {
            var nextChar = (char)sr.Read();
            line.Append(nextChar);

            if (nextChar == lineDelimiter[matchIndex])
            {
                if (matchIndex == lineDelimiter.Length - 1)
                {
                    return line.ToString().Substring(0, line.Length - lineDelimiter.Length);
                }
                matchIndex++;
            }
            else
            {
                matchIndex = 0;
                //did we mistake one of the characters as the delimiter? If so let's restart our search with this character...
                if (nextChar == lineDelimiter[matchIndex])
                {
                    if (matchIndex == lineDelimiter.Length - 1)
                    {
                        return line.ToString().Substring(0, line.Length - lineDelimiter.Length);
                    }
                    matchIndex++;
                }
            }
        }

        return line.Length == 0
            ? null
            : line.ToString();
    }

And it is called like this...

using (StreamReader reader = new StreamReader(file))
{
    string line;
    while((line = reader.ReadLine("\r\n")) != null)
    {
        Console.WriteLine(line);
    }
}