what's about "/" ?? it's also invalid

also:

• @
• [
• ]
• "whitespace"

...and a multitude of others...these 5 are helpful but I could just as easily use a switch statement to escape those 5. perhaps a more comprehensive method could be provided....

using System;
using System.IO;
using System.Security;
using System.Xml;

namespace ReadXMLSalesDataAPI
{
public class PreProcessXML// : IPreProcessXML
{
private string xmlFilename;

/// <param name="_xmlFilename">The filename of the XML document to be converted.</param>
public PreProcessXML(string _xmlFilename)
{
xmlFilename = _xmlFilename;
}

/// <summary>Read the XML file.</summary>
public void ConvertXMLDocument(long linenumber, int lineposition, string exception)
{
try
{
string filepath = xmlFilename;

StreamReader strm;
string strline;
string tempfile = "C:\\Temp.xml";//temporay XML document, for reading from

try
{
File.Copy(filepath, tempfile, true);
}
catch (Exception ex)
{
Console.WriteLine(ex.ToString());
}

StreamWriter strmwriter = new StreamWriter(filepath);
strmwriter.AutoFlush = true;
strm = new StreamReader(tempfile);
int i = 0;

//get the first part of the XML document, upto the invalid character
string line = "";
string errorLine = "";
while ((line = strm.ReadLine()) != null)
{
//get a string containing the correct line
if (i == (linenumber - 1))
{
errorLine = line;
Console.WriteLine("Line num " + i + ", where invalid character is: " + errorLine);
break;
}
else
{
strline = line;
strmwriter.WriteLine(strline);
}

i++;
}
strm.Close();

//check that an invalid characters such as '£' pound sign has not been found
if (!exception.Contains("Invalid character in the given encoding"))
{
//next get the correct line position, which is to be replaced with an XML safe equivalent
string strToReplace = errorLine.Substring(lineposition - 2, 1);
//Console.WriteLine("Char to replace is: " + strToReplace);

//line with the valid character replaced
string newLine = errorLine.Substring(0, lineposition - 2);
// Console.WriteLine("First part is: " + newLine);

//check that a pound sign has not been found
if (SecurityElement.Escape(strToReplace).Trim() != string.Empty)
{
newLine += SecurityElement.Escape(strToReplace);
}
else
{
newLine += strToReplace;
}

//Console.WriteLine("Escape character added is: " + SecurityElement.Escape(strToReplace));
newLine += errorLine.Substring(lineposition - 1);
//Console.WriteLine("Finally Converted line is: " + newLine);

strmwriter.WriteLine(newLine);

strToReplace = SecurityElement.Escape(strToReplace);

//Console.WriteLine("After Conversion, Char to replace with is: " + strToReplace);
}
else
{
strmwriter.WriteLine(errorLine);
}

line = "";
strm = new StreamReader(tempfile);
i = 0;

//get the rest of the XML document after the XML character
while ((line = strm.ReadLine()) != null)
{
//get the rest of the document
if (i >= linenumber)
{
strline = line;
strmwriter.WriteLine(strline);
}

i++;
}

strm.Close();
strm = null;

strmwriter.Flush();
strmwriter.Close();
strmwriter = null;

//finally delete the temporary XML file to free resources, as it is finished with
File.Delete(tempfile);
}
catch(Exception e)
{
Console.WriteLine(e.ToString());
}
}

/// <summary>Attempt to load the XML document. This will determine if the document,
/// contains any errors or not.</summary>
public XmlDocument LoadXMLDoc()
{
XmlDocument xdoc;
int lineNum;
int linePos;

xdoc = new XmlDocument();

try
{
xdoc.Load(xmlFilename);
}
catch (XmlException ex)
{
Console.WriteLine("Exception: " + ex.Message);
lineNum = ex.LineNumber;
linePos = ex.LinePosition;

if (lineNum != 0)
{
if (linePos != 0)
{
ConvertXMLDocument(lineNum, linePos, ex.Message);

LoadXMLDoc();
}
}
}

return (xdoc);
}
}
}