Question

How can I convert a single datarow (of a datatable) into a CSV like string with only few C# commands.
In other words into a string like “value_1;value_2;…;value_n”

Answer 1

Quick and dirty for a single DataRow:

System.Data.DataRow row = ...;

string csvLine = String.Join(
    CultureInfo.CurrentCulture.TextInfo.ListSeparator,
    row.ItemArray);

If you do not care about the culture specific separator you may do this to convert a full DataTable:

public static string ToCsv(System.Data.DataTable table)
{
    StringBuilder csv = new StringBuilder();

    foreach (DataRow row in table.Rows)
        csv.AppendLine(String.Join(";", row.ItemArray));

    return csv.ToString();
}

Here a more complex example if you need to handle a little bit of formatting for the values (in case they’re not just numbers).

public static string ToCsv(DataTable table)
{
    StringBuilder csv = new StringBuilder();
    
    foreach (DataRow row in table.Rows)
    {
        for (int i = 0; i < row.ItemArray.Length; ++i)
        {
            if (i > 0)
                csv.Append(CultureInfo.CurrentCulture.TextInfo.ListSeparator);
    
            csv.Append(FormatValue(row.ItemArray[i]));
        }
    
        csv.AppendLine();
    }
    
    return csv.ToString();
}

Or, if you prefer LINQ (and assuming table is not empty):

public static string ToCsv(DataTable table, string separator = null)
{
    if (separator == null)
        separator = CultureInfo.CurrentCulture.TextInfo.ListSeparator;

    return table.Rows
        .Cast<DataRow>()
        .Select(r => String.Join(separator, r.ItemArray.Select(c => FormatValue(c)))
        .Aggregate(new StringBuilder(), (result, line) => result.AppendLine(line))
        .ToString();
}

Using this private function to format a value. It’s a very naive implementation, for non primitive types you should use TypeConverter (if any, see this nice library: Universal Type Converter) and quote the text only if needed (2.6):

private static string FormatValue(object value)
{
    if (Object.ReferenceEquals(value, null))
        return "";

    Type valueType = value.GetType();

    if (valueType.IsPrimitive || valueType == typeof(DateTime))
        return value.ToString();

    return String.Format("\"{0}\"",
        value.ToString().Replace("\"", "\"\"");
}

Notes
Even if there is a RFC for CSV many applications does not follow its rules and they handle special cases in their very own way (Microsoft Excel, for example, uses the locale list separator instead of comma and it doesn’t handle newlines in strings as required by the standard).