c# - Better way to detect XML?

Question

Currently, I have the following c# code to extract a value out of text. If its XML, I want the value within it - otherwise, if its not XML, it can just return the text itself.

String data = "..."
try
{
    return XElement.Parse(data).Value;
}
catch (System.Xml.XmlException)
{
    return data;
}

I know exceptions are expensive in C#, so I was wondering if there was a better way to determine if the text I'm dealing with is xml or not?

I thought of regex testing, but I dont' see that as a cheaper alternative. Note, I'm asking for a less expensive method of doing this.

Answer 1

You could do a preliminary check for a < since all XML has to start with one and the bulk of all non-XML will not start with one.

(Free-hand written.)

// Has to have length to be XML
if (!string.IsNullOrEmpty(data))
{
    // If it starts with a < after trimming then it probably is XML
    // Need to do an empty check again in case the string is all white space.
    var trimmedData = data.TrimStart();
    if (string.IsNullOrEmpty(trimmedData))
    {
       return data;
    }

    if (trimmedData[0] == '<')
    {
        try
        {
            return XElement.Parse(data).Value;
        }
        catch (System.Xml.XmlException)
        {
            return data;
        }
    }
}
else
{
    return data;
}

I originally had the use of a regex but Trim()[0] is identical to what that regex would do.