如何使用indexof和substring解析特定的字符串？

Question

int firstTag = source.IndexOf("data-token=");
int lastTag = source.IndexOf("\"href", firstTag);
int startIndex = firstTag + 12;
int endIndex = lastTag + 5;
string authenticityToken = source.Substring(startIndex, endIndex - startIndex);

The string I want to parse is from here:

<a class="bizLink" data-token="-iUzEhgdscgbpj5VMi5zoh54FTeFt8M4mj5nsiodxR5VzZOhniodpj6nFQg0nce3MhUxFSgdxjM4J
jUVzZuNu8o0sREnFSUzISUXzZWh4iodGQfdxR5VzZWh4iodGQfhli6fnce_=" 
                           href="

I want to get only the string between " and " only this:

-iUzEhgdscgbpj5VMi5zoh54FTeFt8M4mj5nsiodxR5VzZOhniodpj6nFQg0nce3MhUxFSgdxjM4J
    jUVzZuNu8o0sREnFSUzISUXzZWh4iodGQfdxR5VzZWh4iodGQfhli6fnce_=

But what I get with my code is this long string I wanted, but also all the rest of the file text.

Answer 1

The sane way would be to use a HTML parser and querying library. I can suggest CsQuery , which is a jQuery-like library in .NET. You could use a selector like a[data-token] to match your anchor, then extract the attribute value.

This is the correct way of doing things.

---

But if you only ever want to get this one attribute and don't do anything with the HTML source ever again, it might be easier to just use a regex, but beware: parsing HTML with regex is evil .

So if all you want to do is just extract this one piece of information, as an exceptional measure, for your information, you could use that:

var m = Regex.Match(source, @"data-token\s*=\s*""(?<token>.+?)""");
var authenticityToken = m.Groups["token"].Value;

But try CsQuery first. It's a much better approach.

Answer 2

Working example http://ideone.com/U224iZ

string start = "data-token=";
  string end = " href";

  string source = "<a class='bizLink' data-token='-iUzEhgdscgbpj5VMi5zoh54FTeFt8M4mj5nsiodxR5VzZOhniodpj6nFQg0nce3MhUxFSgdxjM4JjUVzZuNu8o0sREnFSUzISUXzZWh4iodGQfdxR5VzZWh4iodGQfhli6fnce_=1\" href='";

  int firstTag = source.IndexOf(start);
  int lastTag = source.IndexOf(end, firstTag );
  int startIndex = firstTag + start.Length +1;
  int endIndex = lastTag;
  string authenticityToken = source.Substring(startIndex, endIndex - startIndex -1);
  Console.Write(authenticityToken);
  Console.ReadLine();