Escape invalid XML characters in C#

Question

I have a string that contains invalid XML characters. How can I escape (or remove) invalid XML characters before I parse the string?

Answer 1

As the way to remove invalid XML characters I suggest you to use XmlConvert.IsXmlChar method. It was added since .NET Framework 4 and is presented in Silverlight too. Here is the small sample:

void Main() {     string content = "\v\f\0";     Console.WriteLine(IsValidXmlString(content)); // False      content = RemoveInvalidXmlChars(content);     Console.WriteLine(IsValidXmlString(content)); // True }  static string RemoveInvalidXmlChars(string text) {     var validXmlChars = text.Where(ch => XmlConvert.IsXmlChar(ch)).ToArray();     return new string(validXmlChars); }  static bool IsValidXmlString(string text) {     try {         XmlConvert.VerifyXmlChars(text);         return true;     } catch {         return false;     } } 

And as the way to escape invalid XML characters I suggest you to use XmlConvert.EncodeName method. Here is the small sample:

void Main() {     const string content = "\v\f\0";     Console.WriteLine(IsValidXmlString(content)); // False      string encoded = XmlConvert.EncodeName(content);     Console.WriteLine(IsValidXmlString(encoded)); // True      string decoded = XmlConvert.DecodeName(encoded);     Console.WriteLine(content == decoded); // True }  static bool IsValidXmlString(string text) {     try {         XmlConvert.VerifyXmlChars(text);         return true;     } catch {         return false;     } } 

Update: It should be mentioned that the encoding operation produces a string with a length which is greater or equal than a length of a source string. It might be important when you store a encoded string in a database in a string column with length limitation and validate source string length in your app to fit data column limitation.

Answer 2

Use SecurityElement.Escape

using System; using System.Security;  class Sample {   static void Main() {     string text = "Escape characters ： < > & \" \'";     string xmlText = SecurityElement.Escape(text); //output: //Escape characters ： &lt; &gt; &amp; &quot; &apos;     Console.WriteLine(xmlText);   } } 

Answer 3

If you are writing xml, just use the classes provided by the framework to create the xml. You won't have to bother with escaping or anything.

Console.Write(new XElement("Data", "< > &"));

Will output

<Data>&lt; &gt; &amp;</Data>

If you need to read an XML file that is malformed, do not use regular expression. Instead, use the Html Agility Pack.