Part 1 covered converting the contents of a DataTable into CSV format; this part explains reading a CSV file back into a DataTable.
using System.Collections;
using System.Data;
using System.Text;
using System.IO;
namespace CsvParser
{
Like the CsvWriter class, all methods in the CsvParser class are static. There are four parser methods that return a DataTable from either a string or text stream, and expecting a header line in the CSV source or not. Only one method has a real body, all others just adjust their parameter signature. The implementation is simple: the method reads one "row" of the CSV source at a time and populates a row in the DataTable. The real meat is the private class CsvStream explained below. There is one utility method that returns an unused column name for a DataTable, in case there are no headers in the CSV source or the headers are not unique.
{
public static DataTable Parse(string data, bool headers)
{
return Parse(new StringReader(data), headers);
}
public static DataTable Parse(string data)
{
return Parse(new StringReader(data));
}
public static DataTable Parse(TextReader stream)
{
return Parse(stream, false);
}
public static DataTable Parse(TextReader stream, bool headers)
{
DataTable table = new DataTable();
CsvStream csv = new CsvStream(stream);
string[] row = csv.GetNextRow();
if (row == null)
return null;
if (headers)
{
foreach (string header in row)
{
if (header != null && header.Length > 0 && !table.Columns.Contains(header))
table.Columns.Add(header, typeof(string));
else
table.Columns.Add(GetNextColumnHeader(table), typeof(string));
}
row = csv.GetNextRow();
}
while (row != null)
{
while (row.Length > table.Columns.Count)
table.Columns.Add(GetNextColumnHeader(table), typeof(string));
table.Rows.Add(row);
row = csv.GetNextRow();
}
return table;
}
private static string GetNextColumnHeader(DataTable table)
{
int c = 1;
while (true)
{
string h = "Column" + c++;
if (!table.Columns.Contains(h))
return h;
}
}
The CsvStream class does the actual work – read the CSV source in one character at a time and return meaningful chunks of decoded data, namely data items and rows.
{
private TextReader stream;
public CsvStream(TextReader s)
{
stream = s;
}
public string[] GetNextRow()
{
ArrayList row = new ArrayList();
while (true)
{
string item = GetNextItem();
if (item == null)
return row.Count == 0 ? null : (string[])row.ToArray(typeof(string));
row.Add(item);
}
}
private bool EOS = false;
private bool EOL = false;
private string GetNextItem()
{
if (EOL)
{
// previous item was last in line, start new line
EOL = false;
return null;
}
bool quoted = false;
bool predata = true;
bool postdata = false;
StringBuilder item = new StringBuilder();
while (true)
{
char c = GetNextChar(true);
if (EOS)
return item.Length > 0 ? item.ToString() : null;
if ((postdata || !quoted) && c == ',')
// end of item, return
return item.ToString();
if ((predata || postdata || !quoted) && (c == '\x0A' || c == '\x0D'))
{
// we are at the end of the line, eat newline characters and exit
EOL = true;
if (c == '\x0D' && GetNextChar(false) == '\x0A')
// new line sequence is 0D0A
GetNextChar(true);
return item.ToString();
}
if (predata && c == ' ')
// whitespace preceeding data, discard
continue;
if (predata && c == '"')
{
// quoted data is starting
quoted = true;
predata = false;
continue;
}
if (predata)
{
// data is starting without quotes
predata = false;
item.Append(c);
continue;
}
if (c == '"' && quoted)
{
if (GetNextChar(false) == '"')
// double quotes within quoted string means add a quote
item.Append(GetNextChar(true));
else
// end-quote reached
postdata = true;
continue;
}
// all cases covered, character must be data
item.Append(c);
}
}
private char[] buffer = new char[4096];
private int pos = 0;
private int length = 0;
private char GetNextChar(bool eat)
{
if (pos >= length)
{
length = stream.ReadBlock(buffer, 0, buffer.Length);
if (length == 0)
{
EOS = true;
return '\0';
}
pos = 0;
}
if (eat)
return buffer[pos++];
else
return buffer[pos];
}
}
}
}
And that's about it. In an upcoming part of this article I'll share some NUnit test cases for these classes.
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