一种方法是使用正则表达式。请考虑以下事项：

  string  testString =  < iframe width = \395 \height = \295 \src = \// www.***.com/embed/fdbazqdXBeE\\ \\frameborder = \0 \webkitallowfullscreen mozallowfullscreen allowfullscreen>< / iframe>; 

 System.Text.RegularExpressions.Regex re =  new  System.Text.RegularExpressions.Regex（   src = \（。*？）\）; 

 if （re.IsMatch（testString））{
 System.Console.WriteLine（re.Match（testString）.Value ）; 
 System.Console.WriteLine（re.Match（testString）.Value.Substring（ 5 ）。TrimEnd（ ' '））; 
} 

输出为：

 src =// www.***.com/embed/fdbazqdXBeE
 //www.***.com/embed/fdbazqdXBeE

If i have the iframe of a video like this:

<iframe width="395" height="295" src="//www.***.com/embed/fdbazqdXBeE" frameborder="0" webkitallowfullscreen mozallowfullscreen allowfullscreen></iframe>

and I want to get the source "src" only, how can I do this using C#.

Thanks in advance.

One way is to use regular expressions. Consider the following:

string testString = "<iframe width=\"395\" height=\"295\" src=\"//www.***.com/embed/fdbazqdXBeE\" frameborder=\"0\" webkitallowfullscreen mozallowfullscreen allowfullscreen></iframe>";

System.Text.RegularExpressions.Regex re = new System.Text.RegularExpressions.Regex("src=\"(.*?)\"");

if (re.IsMatch(testString)) {
   System.Console.WriteLine(re.Match(testString).Value);
   System.Console.WriteLine(re.Match(testString).Value.Substring(5).TrimEnd('"'));
}

The output is:

src="//www.***.com/embed/fdbazqdXBeE"
//www.***.com/embed/fdbazqdXBeE