(Updated 2018-03-17)

The problem:

The problem, as you've spotted, is that String.Contains does not perform a word-boundary check, so Contains("float") will return true for both "foo float bar" (correct) and "unfloating" (which is incorrect).

The solution is to ensure that "float" (or whatever your desired class-name is) appears alongside a word-boundary at both ends. A word-boundary is either the start (or end) of a string (or line), whitespace, certain punctuation, etc. In most regular-expressions this is \b. So the regex you want is simply: \bfloat\b.

A downside to using a Regex instance is that they can be slow to run if you don't use the .Compiled option - and they can be slow to compile. So you should cache the regex instance. This is more difficult if the class-name you're looking for changes at runtime.

Alternatively you can search a string for words by word-boundaries without using a regex by implementing the regex as a C# string-processing function, being careful not to cause any new string or other object allocation (e.g. not using String.Split).

Approach 1: Using a regular-expression:

Suppose you just want to look for elements with a single, design-time specified class-name:

class Program {


private static readonly Regex _classNameRegex = new Regex( @"\bfloat\b", RegexOptions.Compiled );


private static IEnumerable<HtmlNode> GetFloatElements(HtmlDocument doc) {
return doc
.Descendants()
.Where( n => n.NodeType == NodeType.Element )
.Where( e => e.Name == "div" && _classNameRegex.IsMatch( e.GetAttributeValue("class", "") ) );
}
}

If you need to choose a single class-name at runtime then you can build a regex:

private static IEnumerable<HtmlNode> GetElementsWithClass(HtmlDocument doc, String className) {


Regex regex = new Regex( "\\b" + Regex.Escape( className ) + "\\b", RegexOptions.Compiled );


return doc
.Descendants()
.Where( n => n.NodeType == NodeType.Element )
.Where( e => e.Name == "div" && regex.IsMatch( e.GetAttributeValue("class", "") ) );
}

If you have multiple class-names and you want to match all of them, you could create an array of Regex objects and ensure they're all matching, or combine them into a single Regex using lookarounds, but this results in horrendously complicated expressions - so using a Regex[] is probably better:

using System.Linq;


private static IEnumerable<HtmlNode> GetElementsWithClass(HtmlDocument doc, String[] classNames) {


Regex[] exprs = new Regex[ classNames.Length ];
for( Int32 i = 0; i < exprs.Length; i++ ) {
exprs[i] = new Regex( "\\b" + Regex.Escape( classNames[i] ) + "\\b", RegexOptions.Compiled );
}


return doc
.Descendants()
.Where( n => n.NodeType == NodeType.Element )
.Where( e =>
e.Name == "div" &&
exprs.All( r =>
r.IsMatch( e.GetAttributeValue("class", "") )
)
);
}

Approach 2: Using non-regex string matching:

The advantage of using a custom C# method to do string matching instead of a regex is hypothetically faster performance and reduced memory usage (though Regex may be faster in some circumstances - always profile your code first, kids!)

This method below: CheapClassListContains provides a fast word-boundary-checking string matching function that can be used the same way as regex.IsMatch:

private static IEnumerable<HtmlNode> GetElementsWithClass(HtmlDocument doc, String className) {


return doc
.Descendants()
.Where( n => n.NodeType == NodeType.Element )
.Where( e =>
e.Name == "div" &&
CheapClassListContains(
e.GetAttributeValue("class", ""),
className,
StringComparison.Ordinal
)
);
}


/// <summary>Performs optionally-whitespace-padded string search without new string allocations.</summary>
/// <remarks>A regex might also work, but constructing a new regex every time this method is called would be expensive.</remarks>
private static Boolean CheapClassListContains(String haystack, String needle, StringComparison comparison)
{
if( String.Equals( haystack, needle, comparison ) ) return true;
Int32 idx = 0;
while( idx + needle.Length <= haystack.Length )
{
idx = haystack.IndexOf( needle, idx, comparison );
if( idx == -1 ) return false;


Int32 end = idx + needle.Length;


// Needle must be enclosed in whitespace or be at the start/end of string
Boolean validStart = idx == 0               || Char.IsWhiteSpace( haystack[idx - 1] );
Boolean validEnd   = end == haystack.Length || Char.IsWhiteSpace( haystack[end] );
if( validStart && validEnd ) return true;


idx++;
}
return false;
}

Approach 3: Using a CSS Selector library:

HtmlAgilityPack is somewhat stagnated doesn't support .querySelector and .querySelectorAll, but there are third-party libraries that extend HtmlAgilityPack with it: namely Fizzler and CssSelectors. Both Fizzler and CssSelectors implement QuerySelectorAll, so you can use it like so:

private static IEnumerable<HtmlNode> GetDivElementsWithFloatClass(HtmlDocument doc) {


return doc.QuerySelectorAll( "div.float" );
}

With runtime-defined classes:

private static IEnumerable<HtmlNode> GetDivElementsWithClasses(HtmlDocument doc, IEnumerable<String> classNames) {


String selector = "div." + String.Join( ".", classNames );


return doc.QuerySelectorAll( selector  );
}

You can solve your issue by using the 'contains' function within your Xpath query, as below:

var allElementsWithClassFloat =
_doc.DocumentNode.SelectNodes("//*[contains(@class,'float')]")

To reuse this in a function do something similar to the following:

string classToFind = "float";
var allElementsWithClassFloat =
_doc.DocumentNode.SelectNodes(string.Format("//*[contains(@class,'{0}')]", classToFind));

You can use the following script:

var findclasses = _doc.DocumentNode.Descendants("div").Where(d =>
d.Attributes.Contains("class") && d.Attributes["class"].Value.Contains("float")
);

I used this extension method a lot in my project. Hope it will help one of you guys.

public static bool HasClass(this HtmlNode node, params string[] classValueArray)
{
var classValue = node.GetAttributeValue("class", "");
var classValues = classValue.Split(' ');
return classValueArray.All(c => classValues.Contains(c));
}

public static List<HtmlNode> GetTagsWithClass(string html,List<string> @class)
{
// LoadHtml(html);
var result = htmlDocument.DocumentNode.Descendants()
.Where(x =>x.Attributes.Contains("class") && @class.Contains(x.Attributes["class"].Value)).ToList();
return result;
}

If you looking for class in some tag (like or any other). Try this one

 var spans = doc.DocumentNode.SelectNodes("//span"); //or other tag or all nodes


var span_with_class = spans.Where(_ => _.Attributes["class"].Value.Split(' ').Any(b => b.Equals("someClass")));