正在分析用引号分隔的csv逗号

下面是简单而完整的CsvHelper，它实现了从csv数据行到csv数据线的解码行编码。在我的上一个项目中，我想使用FastCSVReader，但它的内部似乎相当复杂，因为我不希望获得最快、最强大的解决方案，所以我写了我的小助手。

/// <summary>
/// CsvHelper
/// </summary>
public static class CsvHelper
{
    #region Public methods
    /// <summary>
    /// Codes fields as a line for csv file
    /// </summary>
    /// <param name="fields"></param>
    /// <returns></returns>
    public static string CodeLine(string[] fields)
    {
        if (fields == null || fields.Length == 0)
            return null;
        var sb = new StringBuilder(1024);
        for (int i = 0; i < fields.Length; i++)
        {
            if (fields[i] != null)
            {
                bool mustBeQuoted = fields[i].Contains("'"") || fields[i].Contains(",");
                if (mustBeQuoted)
                {
                    sb.Append("'"");
                    sb.Append(fields[i].Replace("'"", "'"'""));
                    sb.Append("'"");
                }
                else
                {
                    sb.Append(fields[i]);
                }
            }
            if (i != fields.Length - 1)
                sb.Append(",");
        }
        return sb.ToString();
    }
    /// <summary>
    /// Decodes line from csv file into fields
    /// </summary>
    /// <param name="line"></param>
    /// <param name="fields"></param>
    /// <returns>Returns true if decoding was successful</returns>
    public static bool DecodeLine(string line, out string[] fields)
    {
        fields = null;
        if (string.IsNullOrEmpty(line))
            return false;
        int index = 0;
        var res = new List<string>();
        while (index != line.Length)
        {
            string field;
            if (ReadField(line, ref index, out field))
            {
                res.Add(field);
            }
            else
            {
                return false;
            }
        }
        if (line[line.Length - 1] == ',')
        {
            res.Add(string.Empty);
        }
        fields = res.ToArray();
        return true;
    }
    #endregion
    #region Other methods
    private static bool ReadField(string line, ref int index, out string field)
    {
        field = null;
        if (index >= line.Length)
            return false;
        var sb = new StringBuilder(512);
        int state = 0;
        while (true)
        {
            char c = line[index];
            char? c1 = (index + 1 < line.Length - 1) ? (char?)line[index + 1] : null;
            index++;
            switch (state)
            {
                case 0: // START
                    if (c == '"') //text in field starts by quotation mark, text of filed in quotation marks
                    {
                        state = 4;
                    }
                    else if (c == ',') //empty text of filed
                    {
                        field = sb.ToString();
                        return true;
                    }
                    else
                    {
                        state = 1;
                        sb.Append(c);
                    }
                    break;
                case 1: //Not quoted text in field
                    if (c == '"') // error, cannot contains " in the middle of the field
                    {
                        return false;
                    }
                    else if (c == ',')
                    {
                        field = sb.ToString();
                        return true;
                    }
                    else
                    {
                        sb.Append(c);
                    }
                    break;
                case 3: //Escaping quotation mark
                    if (c == '"') //previous quotation mark was escape char for this quotation mark
                    {
                        state = 4;
                        sb.Append(c);
                    }
                    else //error, cannot contais any other char
                    {
                        return false;
                    }
                    break;
                case 4: //Text in between quotation marks
                    if (c == '"') //closing quoted text or escape char for following qoatation mark - based on which char is following
                    {
                        if (c1 != null && c1.Value == '"') //current quotation mark is escape char for following quotation mark
                        {
                            state = 3;
                        }
                        else
                        {
                            state = 5;
                        }
                    }
                    else
                    {
                        sb.Append(c);
                    }
                    break;
                case 5: //Just after closing quotation mark of quoted text
                    if (c == ',') //closing quoted text
                    {
                        field = sb.ToString();
                        return true;
                    }
                    else //error, cannot contais any other char
                    {
                        return false;
                    }
                    break;
            }
            if (index == line.Length)
            {
                if (state == 1 || state == 5)
                {
                    field = sb.ToString();
                    return true;
                }
                return false;
            }
        }
    }
    #endregion
}

我可能会使用像(["])[^"]*'1|('d+)这样的正则表达式，但当然，这种方法可能需要考虑一些其他格式。