Parsing a csv comma delimited with quotes

Question

Suppose I have an input string:

 String test = "\"item one\",\"item,2\",12345";
 String[] arr = test.Split(',');

The result is:

[0]: "item one"
[1]: "item"
[2]: "2"
[3]: "12345"

But I want:

[0]: "item one"
[1]: "item, 2"
[2]: "12345"

Basically, my input string will have quotes to allow a comma between quotes, that is not a delimiter.

Whats the best way to parse this this line into an array?

Answer 1

I would probably use Regular Expression like (["])[^"]*\1|(\d+) but of course it is possible some other formats might need to be consider with this approach.

Answer 2

Below is simple and complete CsvHelper which implements coding an decoding lines from/to csv data lines. In my last project I wanted to use FastCSVReader but it seemed to be quite complicated inside and because I was not aspiring on fastest and the most robust solution as possible I wrote my little helper.

/// <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
}