How to convert a DataTable to a string in C#?

Late but this is what I use

 public static string ConvertDataTableToString(DataTable dataTable)
    {
        var output = new StringBuilder();

        var columnsWidths = new int[dataTable.Columns.Count];

        // Get column widths
        foreach (DataRow row in dataTable.Rows)
        {
           for(int i = 0; i < dataTable.Columns.Count; i++)
           {
               var length = row[i].ToString().Length;
               if (columnsWidths[i] < length)
                   columnsWidths[i] = length;
           }     
        }

        // Get Column Titles
        for (int i = 0; i < dataTable.Columns.Count; i++)
        {
            var length = dataTable.Columns[i].ColumnName.Length;
               if (columnsWidths[i] < length)
                   columnsWidths[i] = length;
        }

        // Write Column titles
        for (int i = 0; i < dataTable.Columns.Count; i++)
        {
            var text = dataTable.Columns[i].ColumnName;
            output.Append("|" + PadCenter(text, columnsWidths[i] + 2));
        }
        output.Append("|\n" + new string('=', output.Length) + "\n");

        // Write Rows
        foreach (DataRow row in dataTable.Rows)
        {
            for (int i = 0; i < dataTable.Columns.Count; i++)
            {
                var text = row[i].ToString();
                output.Append("|" + PadCenter(text,columnsWidths[i] + 2));
            }
            output.Append("|\n");
        }
        return output.ToString();
    }

    private static string PadCenter(string text, int maxLength)
    {
        int diff = maxLength - text.Length;
        return new string(' ', diff/2) + text + new string(' ', (int) (diff / 2.0 + 0.5));

    } 

Prerequisite

using System.Linq;

then ...

string res = string.Join(Environment.NewLine, 
    results.Rows.OfType<DataRow>().Select(x => string.Join(" ; ", x.ItemArray)));

using(var writer = new StringWriter()) {
    results.WriteXml(writer);
    Console.WriteLine(writer.ToString());
}

Of course the usefulness of this depends on how important the formatting is. If it's just a debug dump, I find XML outputs like this very readable. However, if the formatting is important to you, then you have no choice but to write your own method to do it.