DataSet.WriteXml to string

StringWriter sw = new StringWriter();
dataSet.WriteXml(sw);
string result = sw.ToString();

Write to a StringWriter, and then call ToString on that.

Note that if you want the generated XML declaration to specify UTF-8 instead of UTF-16, you'll need something like my Utf8StringWriter.

here is the vb.net code:

 Private Function GenerateXML(ByVal ds As DataSet) As String
    Dim obj As New StringWriter()
    Dim xmlstring As String
    ds.WriteXml(obj)
    xmlstring  = obj.ToString()
    Return xmlstring 
End Function

public string ConvertDatatableToXML(DataTable dt)

        MemoryStream str = new MemoryStream();
        dt.WriteXml(str, true);
        str.Seek(0, SeekOrigin.Begin);
        StreamReader sr = new StreamReader(str);
        string xmlstring = "";
        xmlstring = sr.ReadToEnd();
        return (xmlstring);