System.IO.StreamReader.ReadLine C# (CSharp) Method

        public override string ReadLine()
        {
            if (_stream == null)
            {
                throw new ObjectDisposedException(null, SR.ObjectDisposed_ReaderClosed);
            }

            CheckAsyncTaskInProgress();

            if (_charPos == _charLen)
            {
                if (ReadBuffer() == 0)
                {
                    return null;
                }
            }

            StringBuilder sb = null;
            do
            {
                int i = _charPos;
                do
                {
                    char ch = _charBuffer[i];
                    // Note the following common line feed chars:
                    // \n - UNIX   \r\n - DOS   \r - Mac
                    if (ch == '\r' || ch == '\n')
                    {
                        string s;
                        if (sb != null)
                        {
                            sb.Append(_charBuffer, _charPos, i - _charPos);
                            s = sb.ToString();
                        }
                        else
                        {
                            s = new string(_charBuffer, _charPos, i - _charPos);
                        }
                        _charPos = i + 1;
                        if (ch == '\r' && (_charPos < _charLen || ReadBuffer() > 0))
                        {
                            if (_charBuffer[_charPos] == '\n')
                            {
                                _charPos++;
                            }
                        }
                        return s;
                    }
                    i++;
                } while (i < _charLen);
                i = _charLen - _charPos;
                if (sb == null)
                {
                    sb = new StringBuilder(i + 80);
                }
                sb.Append(_charBuffer, _charPos, i);
            } while (ReadBuffer() > 0);
            return sb.ToString();
        }

        private static void ReadStudentsInfoFromFile(string filePath, SortedDictionary<string, SortedSet<Student>> courses)
        {
            using (StreamReader reader = new StreamReader(filePath))
            {
                string line = reader.ReadLine();
                while (line != string.Empty && line != null)
                {
                    string[] data = line.Split('|');
                    string firstName = data[0].Trim();
                    string lastName = data[1].Trim();
                    string courseName = data[2].Trim();

                    if (courses.ContainsKey(courseName))
                    {
                        courses[courseName].Add(new Student(firstName, lastName));
                    }
                    else
                    {
                        courses[courseName] = new SortedSet<Student>();
                        courses[courseName].Add(new Student(firstName, lastName));
                    }

                    line = reader.ReadLine();
                }
            }
        }