asked on

c# randomize duplicates using now.datetime.milliseconds seed

I have the following code I am using as an asp upload form. This line :

int randomNum = new Random().Next(1000000, 9000000);

is generating duplicate numbers if run very quickly due to the fact that it uses the system time as a seed. How can I fix this? Please provide code I can test and points will be awarded quickly! Thanks!

<%@ Import Namespace="System"%>
<%@ Import Namespace="System.IO"%>
<%@ Import Namespace="System.Net"%>
<%@ Import NameSpace="System.Web"%>
 
<Script language="C#" runat=server>
void Page_Load(object sender, EventArgs e) {
	
int randomNum = new Random().Next(1000000, 9000000);
    
   foreach(string f in Request.Files.AllKeys) {
       HttpPostedFile file = Request.Files[f];
       file.SaveAs("Z:\\ThreatUploads\\ScanMe\\" + file.FileName);
   }
}
</Script>

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JimBrandley

Try using system ticks for the seed as:

int randomNum = new Random(unchecked((int)DateTime.Now.Ticks)).Next(1000000, 9000000);

Page events should take more than a single tick.

Jim

bluedragon99

ASKER

Just tried it, still getting occasional duplicates...not sure exactly why as you would think there would be enough of a delay

JimBrandley

One tick is 100ns. I do not understand how you are firing successive page load events in less time than that unless you have a very fast server and lots of users.

The code you posted doesn't seem to be using the value returned. How do you intend to use it?

Jim

bluedragon99

ASKER

<%@ Import Namespace="System"%>
<%@ Import Namespace="System.IO"%>
<%@ Import Namespace="System.Net"%>
<%@ Import NameSpace="System.Web"%>
 
<Script language="C#" runat=server>
void Page_Load(object sender, EventArgs e) {
	
int randomNum = new Random(unchecked((int)DateTime.Now.Ticks)).Next(1000000, 9000000);
 
    
   foreach(string f in Request.Files.AllKeys) {
       HttpPostedFile file = Request.Files[f];
        file.SaveAs("Z:\\ThreatUploads\\ScanMe\\ScanThis_55185588\\" + randomNum + "_" + file.FileName);
   }
}
</Script>

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bluedragon99

ASKER

1066211
1563676
2775668
2775668
8568747

JimBrandley

I will scratch my head for a time and see if I can think of an alternative.

Jim

JimBrandley

I think I have a solution. Try the code below.

Jim

<%@ Import Namespace="System"%>
<%@ Import Namespace="System.IO"%>
<%@ Import Namespace="System.Net"%>
<%@ Import NameSpace="System.Web"%>
 
<Script language="C#" runat=server>
void Page_Load(object sender, EventArgs e) {
   
   int seed = 0;
   Object seedObject = Application["RndFileSeed"];
   if (seedObject == null)
      seed = unchecked((int)DateTime.Now.Ticks);
   else
      seed = (int)seedObject;
 
   int randomNum = new Random(seed).Next(1000000, 9000000);
 
    
   foreach(string f in Request.Files.AllKeys) {
       HttpPostedFile file = Request.Files[f];
        file.SaveAs("Z:\\ThreatUploads\\ScanMe\\ScanThis_55185588\\" + randomNum + "_" + file.FileName);
   }
   Application.Lock();
   Application["RndFileSeed"] = randomNum.Next();
   Application.UnLock();
 
}
</Script>

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bluedragon99

ASKER

trying...

bluedragon99

ASKER

Server Error in '/' Application.
--------------------------------------------------------------------------------
 
Compilation Error 
Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately. 
 
Compiler Error Message: CS0117: 'int' does not contain a definition for 'Next'
 
Source Error:
 
 
 
Line 22:    }
Line 23:    Application.Lock();
Line 24:    Application["RndFileSeed"] = randomNum.Next();
Line 25:    Application.UnLock();
Line 26:

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JimBrandley

Sorry. This will fix it.

Jim

<%@ Import Namespace="System"%>
<%@ Import Namespace="System.IO"%>
<%@ Import Namespace="System.Net"%>
<%@ Import NameSpace="System.Web"%>
 
<Script language="C#" runat=server>
void Page_Load(object sender, EventArgs e) {
   
   int seed = 0;
   Object seedObject = Application["RndFileSeed"];
   if (seedObject == null)
      seed = unchecked((int)DateTime.Now.Ticks);
   else
      seed = (int)seedObject;
 
   Random rnd = new Random(seed);
   int randomNum = rnd.Next(1000000, 9000000);
 
    
   foreach(string f in Request.Files.AllKeys) {
       HttpPostedFile file = Request.Files[f];
        file.SaveAs("Z:\\ThreatUploads\\ScanMe\\ScanThis_55185588\\" + randomNum + "_" + file.FileName);
   }
   Application.Lock();
   Application["RndFileSeed"] = rnd.Next();
   Application.UnLock();
 
}
</Script>

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bluedragon99

ASKER

1999892
5073422
6839206
7176987
7600909
7600909

<%@ Import Namespace="System"%>
<%@ Import Namespace="System.IO"%>
<%@ Import Namespace="System.Net"%>
<%@ Import NameSpace="System.Web"%>
 
<Script language="C#" runat=server>
void Page_Load(object sender, EventArgs e) {
   
   int seed = 0;
   Object seedObject = Application["RndFileSeed"];
   if (seedObject == null)
      seed = unchecked((int)DateTime.Now.Ticks);
   else
      seed = (int)seedObject;
 
   Random rnd = new Random(seed);
   int randomNum = rnd.Next(1000000, 9000000);
    
   foreach(string f in Request.Files.AllKeys) {
       HttpPostedFile file = Request.Files[f];
        file.SaveAs("Z:\\ThreatUploads\\ScanMe\\ScanThis_433609376\\" + randomNum + "_" + file.FileName);
   
}
   Application.Lock();
   Application["RndFileSeed"] = rnd.Next();
   Application.UnLock();
 
}
</Script>

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JimBrandley

Are you testing this on a web farm?

Jim

bluedragon99

ASKER

1 IIS 6.0 server

JimBrandley

Is the 7 digit randomizer a requirement, or could you take any random value? I'm wobdering if a GUID would better serve your needs.

Jim

bluedragon99

ASKER

any random number would be perfectly fine..

JimBrandley

Excellect! Then this will work.

Jim

<%@ Import Namespace="System"%>
<%@ Import Namespace="System.IO"%>
<%@ Import Namespace="System.Net"%>
<%@ Import NameSpace="System.Web"%>
 
<Script language="C#" runat=server>
void Page_Load(object sender, EventArgs e) {
   string guid = System.Guid.NewGuid().ToString("N")).ToUpper();
 
   foreach(string f in Request.Files.AllKeys) {
       HttpPostedFile file = Request.Files[f];
        file.SaveAs("Z:\\ThreatUploads\\ScanMe\\ScanThis_55185588\\" + guid + "_" + file.FileName);
   }
}
</Script>

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bluedragon99

ASKER

misising semi colon somewhere?

Compilation Error 
Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately. 
 
Compiler Error Message: CS1002: ; expected
 
Source Error:
 
 
 
Line 6:  <Script language="C#" runat=server>
Line 7:  void Page_Load(object sender, EventArgs e) {
Line 8:     string guid = System.Guid.NewGuid().ToString("N")).ToUpper();
Line 9:   
Line 10:    foreach(string f in Request.Files.AllKeys) {

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JimBrandley

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bluedragon99

ASKER

mid(System.Guid.NewGuid().ToString("N").ToUpper(),1,5);

how do I capture the first five characters? (using as a filename)

JimBrandley

(System.Guid.NewGuid().ToString("N").ToUpper()).Substring(0,5);

Jim