QueryString always return null after server.UrlDecode

Question

My page url is very simple EmailToFriend.aspx?PID=5&Lang=en-US

    string _pid= Server.UrlDecode(Request.QueryString["PID"]);
    string _lang = Server.UrlDecode(Request.QueryString["Lang"]);

result:

_pid=5
_lang= null

I am trying to get QueryString value of both PID and Lang but it return null for lang value while it is present in the url i.e= en-US

While debugging i noticed that it show url as PID=5&amp%3bLang=en-US for following line of code

string _lang = Server.UrlDecode(Request.QueryString["Lang"]);

I am not sure what is wrong and why it is showing %3b in place of ;

How can i resolve this so that i get the value for QueryString lang

If i use only & in my url then it works fine with request["lang"]; problem only happens when i encode url & try to decode it back

article reference http://msdn.microsoft.com/en-us/library/6196h3wt%28v=vs.110%29.aspx

doesn't work for me..

I don't think you need Server.UrlDecode because Request.QueryString will return a URL decoded value by default. — johna
– johna, Commented Feb 4, 2014 at 1:47

IronGeek · Accepted Answer · 2014-02-03 08:34:20Z

First, from Wikipedia: a query string is the part of a (URL) that contains data to be passed to web applications, it is encoded as follows:

field1=value1&field2=value2&field3=value3...

The query string is composed of a series of field-value pairs.
Within each pair, the field name and value are separated by an equals sign, '='.
The series of pairs is separated by the ampersand, '&'...

Thus, when you have a url as follows:

EmailToFriend.aspx?PID=5&Lang=en-US

You have a querystring with two field-value pairs, separated by ampersand ('&'):

"PID" => "5", and "amp;Lang" => "en-US"

...

Now, back to your problem:

I am trying to get QueryString value of both PID and Lang but it return null for lang value while it is present in the url i.e= en-US

The reason why Lang always returns null, is because the key does not exist in the qiven URL, instead the key amp;Lang exist with the value en-US. You can verify this using the following code:
```
string _amplang = Server.UrlDecode(Request.QueryString["amp;Lang"]);
```
How can i resolve this so that i get the value for QueryString lang

You've basically answered this one yourself. Its by fixing your URL and use the correct form of querystring: EmailToFriend.aspx?PID=5&Lang=en-US
article reference http://msdn.microsoft.com/en-us/library/6196h3wt%28v=vs.110%29.aspx doesn't work for me..

It does work, but unfortunately you're working it wrong. The URL encoded value of ampersand ('&') is %26 not &. The HTML encoded value of ampersand ('&'), on the other hand, is &. You're probably trying to URL-decode an HTML-encoded value.

For example, let's say you have the following URL:

EmailToFriend.aspx?PID=5&Lang=en-US&Url=EmailToFriend.aspx%3fPID%3d5%26Lang%3den-US

If you run the following code:
```
string _pid= Server.UrlDecode(Request.QueryString["PID"]);
string _lang = Server.UrlDecode(Request.QueryString["Lang"]);
string _url = Server.UrlDecode(Request.QueryString["Url"]);
```
You'll have the following value:
```
_pid=5
_lang= en-US
_url = EmailToFriend.aspx?PID=5&Lang=en-US
```
The Url value is correctly decoded from the query string.

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