How static variables are stored?

[Murugs]

Friends,
Jus want to know how static variables r stored and accessed.
I believe that static variable will maintain only single copy per application domain.
If so then how does it allow a single static variable to have different values for diff instance.


Cheers,
Murugs.

[r035198x]

Friends,
Jus want to know how static variables r stored and accessed.
I believe that static variable will maintain only single copy per application domain.
If so then how does it allow a single static variable to have different values for diff instance.


Cheers,
Murugs.

Statics are stored once when a class is "loaded" (on the stack). Objects of the same class share one variable that is stored in one memory location for that class. All instances created from that same class (dynamically on the heap) would all have a reference to that same (one memory location) variable which is on the stack.
A single static variable can thus not have different values for different instances of the same class.

[Murugs]

Thanks for your reply.
I meant application instance not class instance.

Class GlobalVariables
{
public static string userName;
}

consider we have one login page.
In Login.aspx.cs page i am assigning some values for userName like

GlobalVariables.userName=txtUserName.Text //saving the user entered text to that static variable.

now the single static variable can have different values for each application instance(opening 2 instance of an application in 2 diff browsers.)

can you explain the above scenario?

Thanks,
Murugs.

[r035198x]

Thanks for your reply.
I meant application instance not class instance.

Class GlobalVariables
{
public static string userName;
}

consider we have one login page.
In Login.aspx.cs page i am assigning some values for userName like

GlobalVariables.userName=txtUserName.Text //saving the user entered text to that static variable.

now the single static variable can have different values for each application instance(opening 2 instance of an application in 2 diff browsers.)

can you explain the above scenario?

Thanks,
Murugs.

Two different applications would run from different memory locations and would have therefore not share the same statics for instance variables.

[Murugs]

Same application opened in 2 different browsers.not 2 different application.
Say for example,I have opened 2 internet explorer.now i am accessing thescripts.com in both the IE's.

[Plater]

Same application opened in 2 different browsers.not 2 different application.
Say for example,I have opened 2 internet explorer.now i am accessing thescripts.com in both the IE's.

The server is running the applications, not the browser, so it doesn't care who opened what number of browsers.
Seems like you should be storing those values in the Session object, not in a static class anyway.

[r035198x]

Same application opened in 2 different browsers.not 2 different application.
Say for example,I have opened 2 internet explorer.now i am accessing thescripts.com in both the IE's.

The code for the GlobalVariables class runs on the server not the client side. So multiple clients connecting would all have the same instance of the GlobalVariables class (unless it's defined at session level: I'm not sure if that's possible or how that can be done) and therefore share the same value for the userName field.

Edit: And as usual Plater beat me to it ...

[Murugs]

HI Plater,
You have misunderstood my question.
As you said server is running the application,how does the server handles static variable in the above scenorio.Thats my question.
Yes you are correct.we can use session object for that purpose.
My next question is which one is performance wise better (session or static variable) if both can able to maintain instance specific data's.
Thats why i am little bit confused :(

Regards,
Murugs.

[Murugs]

Hi r035198x ,
Yes that is possible.we can store instance specific data in static variables.
I have done a small poc on that and its working.

-Murugs

[r035198x]

HI Plater,
You have misunderstood my question.
As you said server is running the application,how does the server handles static variable in the above scenorio.Thats my question.
Yes you are correct.we can use session object for that purpose.
My next question is which one is performance wise better (session or static variable) if both can able to maintain instance specific data's.
Thats why i am little bit confused :(

Regards,
Murugs.

Read Plater's response again and the one I made after that. The statics are handled in the same way that I've been describing above. Storing values as static variables of a class and storing them in the session are not the same thing. Storing in the static variables is not "able to store instance specific data".

[r035198x]

Hi r035198x ,
Yes that is possible.we can store instance specific data in static variables.
I have done a small poc on that and its working.

-Murugs

I give up then.
You simply can't have two diffrent instances of the same class having different values of the same static variable at the same time in the same application.

[Plater]

If you have a web application (ASP.NET)
And you have code like:

public class myclass
{
   public static int Myint=30;
}
 

It is my understanding that there is only ONE instance of that Myint variable, regardless fo what client opens how many browsers.
So setting that value should change it for everyone.

Session is certainly prefered over statics for maintaining information that is only relevant to the "current user"

[Murugs]

Please just do this sample page

class GlobalVariables
{
public static string userName;
public static string sessionValue;
}

aspx page
//Have a textbox by the name txtUserName to allow the user to enter somevalue
//Have a button by the name btnSubmit
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class Default6 : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{

}
protected void btnSubmit_Click(object sender, EventArgs e)
{
GlobalVariables.sessionValue=Session.SessionID;
Response.Write(GlobalVariables.sessionValue);
Response.Write("<br>");
GlobalVariables.userName=txtUserName.Text;
Response.Write(GlobalVariables.userName);
}
}
now run http://localhost/test/Default6.aspx in two IE.
Enter some name in the textbox in both the ie's and click the submit button.Now you can able to see GlobalVariables.sessionValue and GlobalVariables.userName has two different values.
How does the static variable can able to maintain 2 different values?
I hope now u can understand my question.
Please run the above sample and send me ur replies.

Cheers,
Murugs.

[r035198x]

Please just do this sample page

class GlobalVariables
{
public static string userName;
public static string sessionValue;
}

aspx page
//Have a textbox by the name txtUserName to allow the user to enter somevalue
//Have a button by the name btnSubmit
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class Default6 : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{

}
protected void btnSubmit_Click(object sender, EventArgs e)
{
GlobalVariables.sessionValue=Session.SessionID;
Response.Write(GlobalVariables.sessionValue);
Response.Write("<br>");
GlobalVariables.userName=txtUserName.Text;
Response.Write(GlobalVariables.userName);
}
}
now run http://localhost/test/Default6.aspx in two IE.
Enter some name in the textbox in both the ie's and click the submit button.Now you can able to see GlobalVariables.sessionValue and GlobalVariables.userName has two different values.
How does the static variable can able to maintain 2 different values?
I hope now u can understand my question.
Please run the above sample and send me ur replies.

Cheers,
Murugs.

I can't try that code now with the way I've setup my mono (but mostly because I hate .NET programs passionately) but it doesn't look like you have a static variable holding two different values for different instance objects. All I see is something with the following structure

string myVal = "first";
myVal = "second";
myVal = "third";
//...

at any one point the variable myVal is always storing one value.
The previous value is being overwritten bythe new value. That is all you are doing in your program. Simple overwritting of the same variable with different values.

[Murugs]

As you said,after execution of line 3 the variable myVal will hold only the value "third".But in my case its maintaining different values.
Thats why i confused abt the storage of Static variables...

[Plater]

That doesn't actually have two different values.
Each page load stores it's value in that static, then spits it back out to the page.
The next page overwrites that value with it's own, then shows it again.
That is not a valid test.

[Murugs]

Hi Plater,
Just update the static variable on some condition and check it again.
its maintaining different values.
check the below code.

GlobalVariables.userName = "Value not changed";
Response.Write(GlobalVariables.userName);
if (Request.QueryString["Id"] == "1")
{
GlobalVariables.userName="value changed";
Response.Write(GlobalVariables.userName);
}

run the application in two ies.
Now pass the Id =1 as querystring in one ie.

Now check you can have different values.
Let me know if you are not understand my question..pls do some sample before reply so u can able to know my question well.
Thanks..

-Murugs

[Plater]

Hi Plater,
Just update the static variable on some condition and check it again.
its maintaining different values.
check the below code.

GlobalVariables.userName = "Value not changed";
Response.Write(GlobalVariables.userName);
if (Request.QueryString["Id"] == "1")
{
GlobalVariables.userName="value changed";
Response.Write(GlobalVariables.userName);
}

run the application in two ies.
Now pass the Id =1 as querystring in one ie.

Now check you can have different values.
Let me know if you are not understand my question..pls do some sample before reply so u can able to know my question well.
Thanks..

-Murugs

AGAIN, you are SETTING the value each time and overwriting the previous value. You don't see it happening because it will print it out before the next page is loaded

Create a page with two buttons and label.

protected void Page_Load(object sender, EventArgs e)
{
   MyLabel.Text=GlobalVars.thinger;
}
protected void btChange_Click(object sender, EventArgs e)
{
   GlobalVars.thinger = Request.RawUrl;
}
protected void btView_Click(object sender, EventArgs e)
{//do nothing
}
 

Make sure you have something like:

public static class GlobalVars
{
   public static string thinger="";
}
 

Then you can do your two broswers test, changing the querystring and using the "change" button to set the global variable and use the View button to view it.

[Murugs]

Atlast got it.its all coz of wrong testing..
Thanks Plater..