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• Node & Redis: Crucial Design Issues in Production Mode

  - by Ali

  This question is a hybrid one, being both technical and system design related. I'm developing the backend of an application that will handle approx. 4K request per second. We are using Node.js being super fast and in terms of our database struction we are using MongoDB, with Redis being a layer between Node and MongoDB handling volatile operations. I'm quite stressed because we are expecting concurrent requests that we need to handle carefully and we are quite close to launch. However I do not believe I've applied the correct approach on redis. I have a class Student, and they constantly change stages(such as 'active', 'doing homework','in lesson' etc. Thus I created a Redis DB for each state. (1 for being 'active', 2 for being 'doing homework'). Above I have the structure of the 'active' students table; xa5p - JSON stringified object #1 pQrW - JSON stringified object #2 active_student_table - {{studentId:'xa5p'}, {studentId:'pQrW'}} Since there is no 'select all keys method' in Redis, I've been suggested to use a set such that when I run command 'smembers' I receive the keys and later on do 'get' for each id in order to find a specific user (lets say that age older than 15). I've been also suggested that in fact I used never use keys in production mode. My question is, no matter how 'conceptual' it is, what specific things I should avoid doing in Node & Redis in production stage?. Are they any issues related to my design? Students must be objects and I sure can list them in a list but I haven't done yet. Is it that crucial in production stage?

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• Problems running XNA game on 64-bit Windows 7

  - by Tesserex

  I'm having problems getting my game engine to run on my brother's machine, which is running 64-bit Windows 7. I'm developing on 32-bit XP SP2. My app uses XNA, FMOD.NET, and another dll I wrote entirely in C#. Everything is targeted to x86, not AnyCPU. I've read that this is required for XNA to work because there is no 64-bit xna framework. I recompiled FMOD.NET as x86 as well and made sure to be using the 32-bit version of the native dll. So I don't see any problems there. However when he tries to run my app, it gives an error which is mysterious, but not unheard of. A FileNotFoundException with an empty file name, and the top of the stack trace is in my main form constructor. The message is The specified module could not be found. (Exception from HRESULT: 0x8007007E) I found some threads online about this error, all with very vague, mixed, and fuzzy responses that don't really help me. Most remind people to target x86. Some say check that they have all the dlls necessary. I gave my brother Microsoft.Xna.Framework.dll, but does he need to install the entire XNA redistributable package? When I take everything I sent him and stick it in a random directory, it still runs fine for me. I developed the game in VS2008, not in game studio, using XNA 3.0 and a Windows Forms control that uses XNA drawing which I found in an msdn tutorial. I would also like to avoid requiring a full installer if possible. Any insight? Please?

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• What happens when value types are created?

  - by Bob

  I'm developing a game using XNA and C# and was attempting to avoid calling new struct() type code each frame as I thought it would freak the GC out. "But wait," I said to myself, "struct is a value type. The GC shouldn't get called then, right?" Well, that's why I'm asking here. I only have a very vague idea of what happens to value types. If I create a new struct within a function call, is the struct being created on the stack? Will it simply get pushed and popped and performance not take a hit? Further, would there be some memory limit or performance implications if, say, I need to create many instances in a single call? Take, for instance, this code: spriteBatch.Draw(tex, new Rectangle(x, y, width, height), Color.White); Rectangle in this case is a struct. What happens when that new Rectangle is created? What are the implications of having to repeat that line many times (say, thousands of times)? Is this Rectangle created, a copy sent to the Draw method, and then discarded (meaning no memory getting eaten up the more Draw is called in that manner in the same function)? P.S. I know this may be pre-mature optimization, but I'm mostly curious and wish to have a better understanding of what is happening.

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• HTML entity encoding (convert '<' to '&lt;') on iPhone in objective-c

  - by Markus

  I'm developing an application for the iPhone that has inApp-mail sending capabilities. So far so good, but now I want to avoid html-injections as some parts of the mail are user-generated texts. Basically I search for something like this: // inits NSString *sourceString = [NSString stringWithString:@"Hello world! Grüße dich Welt <-- This is in German."]; // ----- THAT'S WHAT I'M LOOKING FOR // pseudo-code | // V NSString *htmlEncodedString = [sourceString htmlEncode]; // log NSLog(@"source string: %@", sourceString); NSLog(@"encoded string: %@", htmlEncodedString); Expected output source string: Hello world! Grüße dich Welt <-- This is in German. encoded string: Hello world! Gr&#252;&#223;e dich Welt &lt;-- This is in German. I already googled and looked through several of SO's questions and answers, but all of them seem to be related to URL-encoding and that's not what I really need (I tried stringByAddingPercentEscapesUsingEncoding with no luck - it creates %C3%BC out of an 'ü' that should be an ü). A code sample would be really great (correcting mine?)... -- Thanks in advance, Markus

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• Looping through an List to select an Element in Selenium

  - by ChrisMcLellan

  I'm attempting to write a Page Class for Links within the Header of the website I'm testing. I have the following link structure below <ul> <li><a href="/" title="Home">Home</a></li> <li><a href="/AboutUs" title="About Us">About Us</a> </li> <li><a href="/Account" title="Account">Account</a></li> <li><a href="/Account/Orders" title="Orders">Orders</a></li> <li><a href="/AdministrationPortal" title="Administration Portal">Administration Portal</a></li> </ul> What I want to do is store these into a List, then when a user select one of the links, it will take then to the page they should go to. I have started with the following code below List<IWebElement> headerElements = new List<IWebElement>(); headerElements.Add(WebDriver.FindElement(By.LinkText("Home"))); headerElements.Add(WebDriver.FindElement(By.LinkText("About Us"))); headerElements.Add(WebDriver.FindElement(By.LinkText("Account"))); headerElements.Add(WebDriver.FindElement(By.LinkText("Orders"))); headerElements.Add(WebDriver.FindElement(By.LinkText("Administration Portal"))); headerElements.Add(WebDriver.FindElement(By.LinkText("Log in / Register"))); headerElements.Add(WebDriver.FindElement(By.LinkText("Log off"))); I was thinking for using a for loop to do this, would this be the best way. I'm trying to avoid writting methods like the one below for each link public void SelectCreateNewReferralLink() { var selectAboutUsLink = ( new WebDriverWait(WebDriver, new TimeSpan(50))).Until (ExpectedConditions.ElementExists(By.CssSelector("#main > a:nth-of-type(1)"))); selectCreateNewReferralLink.Click(); } I'm using C#, with WebDriver attempting to write this Any Help would be great Thanks Chris

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• wxGraphicsContext dreadfully slow on Windows

  - by Jonatan

  I've implemented a plotter using wxGraphicsContext. The development was done using wxGTK, and the graphics was very fast. Then I switched to Windows (XP) using wxWidgets 2.9.0. And the same code is extremely slow. It takes about 350 ms to render a frame. Since the user is able to drag the plotter with the mouse to navigate it feels very sluggish with such a slow update rate. I've tried to implement some parts using wxDC and benchmarked the difference. With wxDC the code runs just about 100 times faster. As far as I know both Cairo and GDI+ are implemented in software at this point, so there's no real reason Cairo should be so much faster than GDI+. Am I doing something wrong? Or is the GDI+ implementation just not up on par with Cairo? One small note: I'm rendering to a wxBitmap now, with the wxGraphicsContext created from a wxMemoryDC. This is to avoid flicker on XP, since double buffering doesn't work there.

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• What's a way for a client to automatically resolve the ip address of a server?

  - by zooropa

  The project I am working on is a client/server architecture. In a LAN environment, I want the client's to be able to automatically determine the server's address. I want to avoid having to manually configure each client with the ip address of the server. What is the best way to do this? Some alternatives I have thought about doing are: The server could listen for broadcast packets from the clients. The message from the client would be a request for the IP address of the server. The server would respond with its address. The machine running my project's server could also have a bind server running. The LAN's router could be configured to use it as one of its DNS servers. I think I saw that there is a bind library. Does that mean I can build the bind service into my server so that bind doesn't have to be installed on the server? Any other ideas? What have you done in the past? What are the pros/cons of these approaches and others that might be suggested? Thanks for your help!

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• MYSQL - SELECT ALL FROM TABLE if...

  - by hornetbzz

  Hello I have a (nice) mysql table built like this : Fields Datas id (pk) 1 2 3 4 5 6 master_id 1000 1000 1000 2000 2000 2000 ... master_name home home home shop shop shop ... type_data value common client value common client ... param_a foo_a 1 0 bar_a 0 1 ... param_b foo_b 1 0 bar_b 1 0 ... param_c foo_c 0 1 bar_c 0 1 ... ... ... ... ... ... ... ... ... All these datas are embed in a single table. Each datas are dispatched on 3 "columns" set (1 for the values, 1 for identifying if these are common values and one for identifying client values). It's not the best I got but many other scripts depends on this structure. I'd need sthg like this: SELECT parameters name (eg param_a, param_b..) and their values (eg foo_a, foo_b..) WHEN master_id=? AND type_data=(common or client) (eg for values=1 on the 2nd column) . in order to get the parameters hash like param_a => foo_a param_b => foo_b param_c => foo_c ... I could not succeed in self joining on the same table till now but I guess it should be feasible. (I'd like to avoid to do several queries) Thx in advance

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• Why does this test fail?

  - by Tomas Lycken

  I'm trying to test/spec the following action method public virtual ActionResult ChangePassword(ChangePasswordModel model) { if (ModelState.IsValid) { if (MembershipService.ChangePassword(User.Identity.Name, model.OldPassword, model.NewPassword)) { return RedirectToAction(MVC.Account.Actions.ChangePasswordSuccess); } else { ModelState.AddModelError("", "The current password is incorrect or the new password is invalid."); } } // If we got this far, something failed, redisplay form return RedirectToAction(MVC.Account.Actions.ChangePassword); } with the following MSpec specification: public class When_a_change_password_request_is_successful : with_a_change_password_input_model { Establish context = () => { membershipService.Setup(s => s.ChangePassword(Param.IsAny<string>(), Param.IsAny<string>(), Param.IsAny<string>())).Returns(true); controller.SetFakeControllerContext("POST"); }; Because of = () => controller.ChangePassword(inputModel); ThenIt should_be_a_redirect_result = () => result.ShouldBeARedirectToRoute(); ThenIt should_redirect_to_success_page = () => result.ShouldBeARedirectToRoute().And().ShouldRedirectToAction<AccountController>(c => c.ChangePasswordSuccess()); } where with_a_change_password_input_model is a base class that instantiates the input model, sets up a mock for the IMembershipService etc. The test fails on the first ThenIt (which is just an alias I'm using to avoid conflict with Moq...) with the following error description: Machine.Specifications.SpecificationException: Should be of type System.RuntimeType but is [null] But I am returning something - in fact, a RedirectToRouteResult - in each way the method can terminate! Why does MSpec believe the result to be null?

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• Symbian: clear buffer of RSocket object

  - by Heinz

  Hi, I have to come back once again to sockets in Symbian. Code to set up a connection to a remote server looks as follows: TInetAddr serverAddr; TUint iPort=111; TRequestStatus iStatus; TSockXfrLength len; TInt res = iSocketSrv.Connect(); res = iSocket.Open(iSocketSrv,KAfInet,KSockStream, KProtocolInetTcp); res = iSocket.SetOpt(KSoTcpSendWinSize, KSolInetTcp, 0x10000); serverAddr.SetPort(iPort); serverAddr.SetAddress(INET_ADDR(11,11,179,154)); iSocket.Connect(serverAddr,iStatus); User::WaitForRequest(iStatus); Over the iSocket i receive packets of variable size. On very few occurences it happens that such a packet is corrupted. What I would like to do then is to clear all the data that is currently in the iSocket buffer and ready to be read. I have not seen any method of RSocket that allows me to clear the content of the buffer. Does anyone know how to do that? If possible, I would like to avoid using RecvOneOrMore() or similar recv function clear the buffer Thanks

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• floating point equality in Python and in general

  - by eric.frederich

  I have a piece of code that behaves differently depending on whether I go through a dictionary to get conversion factors or whether I use them directly. The following piece of code will print 1.0 == 1.0 -> False But if you replace factors[units_from] with 10.0 and factors[units_to ] with 1.0 / 2.54 it will print 1.0 == 1.0 -> True #!/usr/bin/env python base = 'cm' factors = { 'cm' : 1.0, 'mm' : 10.0, 'm' : 0.01, 'km' : 1.0e-5, 'in' : 1.0 / 2.54, 'ft' : 1.0 / 2.54 / 12.0, 'yd' : 1.0 / 2.54 / 12.0 / 3.0, 'mile' : 1.0 / 2.54 / 12.0 / 5280, 'lightyear' : 1.0 / 2.54 / 12.0 / 5280 / 5.87849981e12, } # convert 25.4 mm to inches val = 25.4 units_from = 'mm' units_to = 'in' base_value = val / factors[units_from] ret = base_value * factors[units_to ] print ret, '==', 1.0, '->', ret == 1.0 Let me first say that I am pretty sure what is going on here. I have seen it before in C, just never in Python but since Python in implemented in C we're seeing it. I know that floating point numbers will change values going from a CPU register to cache and back. I know that comparing what should be two equal variables will return false if one of them was paged out while the other stayed resident in a register. Questions What is the best way to avoid problems like this?... In Python or in general. Am I doing something completely wrong? Side Note This is obviously part of a stripped down example but what I'm trying to do is come with with classes of length, volume, etc that can compare against other objects of the same class but with different units. Rhetorical Questions If this is a potentially dangerous problem since it makes programs behave in an undetermanistic matter, should compilers warn or error when they detect that you're checking equality of floats Should compilers support an option to replace all float equality checks with a 'close enough' function? Do compilers already do this and I just can't find the information.

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• Strange layout behaviour

  - by andrii

  I am a little bit confused. Here is an small web page. There are two main div-s: top and mainBlock. First contain image. The problem is that firebug shows that div#top's height is equal to 0 and because of that the next div mainBlock moves up. If I would delete this peace of code: div#logo{ float: left; } everything will start working fine and div#mainBlock will be below the div#top. Could you, please, explain me how it works and how to avoid this in proper way? Here is my code: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/> <title>Paralab - Website &amp; interface design, web apps development, usability</title> <style text="text/css"> html, body{ } div#logo{ float: left; } #top{ width: 100%; } #mainBlock{ width:100%; } </style> </head> <body> <div id="top"> <div id="logo"> <img alt="logo" src="img/logo.png" /> </div> </div> <div id="mainBlock"> Contact Us </div> </body> </html>

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• How can I sign a Windows Mobile application for internal use?

  - by AR

  I'm developing a Windows Mobile application for internal company use, using the Windows Mobile 6 Professional SDK. Same old story: I've developed and tested on the emulator and all is well, but as soon as I deploy to advice I get an UnauthorizedAccessException when writing files or creating directories. I'm aware that an application installed to a device needs to be signed but I'm running into roadblocks at every turn: Using the project properties 'Devices' window I select 'Sign the project output with this certificate, and choose one of the sample certificates from the SDK. This results in a build error: "The signer's certificate is not valid for signing" when running SignTool. If I try to run SignTool.exe from the commandline, I get an error telling me to run SignTool.exe from a location in the system's PATH. I can't use the 'Signing' tab in the Project Properties to create a test certificate - this is greyed out (presumably for WinMobile projects?). If at all possible, I would like to avoid having to go through Versign or the like to get a Mobile2Market certificate. If I have to go this route for a final version that's fine, but I need to at least be able to test the app on real devices. Any advice would be most welcome!

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• MySql Query lag time?

  - by Click Upvote

  When there are multiple PHP scripts running in parallel, each making an UPDATE query to the same record in the same table repeatedly, is it possible for there to be a 'lag time' before the table is updated with each query? I have basically 5-6 instances of a PHP script running in parallel, having been launched via cron. Each script gets all the records in the items table, and then loops through them and processes them. However, to avoid processing the same item more than once, I store the id of the last item being processed in a seperate table. So this is how my code works: function getCurrentItem() { $sql = "SELECT currentItemId from settings"; $result = $this->db->query($sql); return $result->get('currentItemId'); } function setCurrentItem($id) { $sql = "UPDATE settings SET currentItemId='$id'"; $this->db->query($sql); } $currentItem = $this->getCurrentItem(); $sql = "SELECT * FROM items WHERE status='pending' AND id > $currentItem'"; $result = $this->db->query($sql); $items = $result->getAll(); foreach ($items as $i) { //Check if $i has been processed by a different instance of the script, and if so, //leave it untouched. if ($this->getCurrentItem() > $i->id) continue; $this->setCurrentItem($i->id); // Process the item here } But despite of all the precautions, most items are being processed more than once. Which makes me think that there is some lag time between the update queries being run by the PHP script, and when the database actually updates the record. Is it true? And if so, what other mechanism should I use to ensure that the PHP scripts always get only the latest currentItemId even when there are multiple scripts running in parrallel? Would using a text file instead of the db help?

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• Tree data in MySql database table

  - by Robert Koritnik

  I have a table that uses Adjacency list model for hierarchy storage. My most relevant columns in this table are therefore: ItemId // is auto_increment ParentId Level ParentTrail // in the form of "parentId/../parentId/itemId" then I created a before insert tigger, that populates columns Level and ParentTrail. Since the last column also includes current item's ID I had to use a trick in my trigger because auto_increment columns are not available in the before insert trigger. So I get that value from the information_schema.tables table. All works fine, until I try to write an update trigger, that would update my item and its descendants when the item changes its parent (ParentId has changed). But I can't make an update on my table inside the update trigger. All I can do is to change current record's values but not other's. I could use a separate table for hierarchy data, but that would mean that I would also have to create a view that would combine these two tables (1:1 relation) and I would like to avoid this is at all possible. Is there a way to have all these in the same table so that these fields (Level and ParetTrail) set/update themselves automagically using triggers?

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• Trouble creating a SQL query

  - by JoBu1324

  I've been thinking about how to compose this SQL query for a while now, but after thinking about it for a few hours I thought I'd ask the SO community to see if they have any ideas. Here is a mock up of the relevant portion of the tables: contracts id date ar (yes/no) term payments contract_id payment_date The object of the query is to determine, per month, how many payments we expect, vs how many payments we received. conditions for expecting a payment Expected payments begin on contracts.term months after contracts.date, if contracts.ar is "yes". Payments continue to be expected until the month after the first missed payment. There is one other complication to this: payments might be late, but they need to show up as if they were paid on the date expected. The data is all there, but I've been having trouble wrapping my head around the SQL query. I am not an SQL guru - I merely have a decent amount of experience handling simpler queries. I'd like to avoid filtering the results in code, if possible - but without your help that may be what I have to do. Expected Output Month Expected Payments Received Payments January 500 450 February 498 478 March 234 211 April 987 789 ... SQL Fiddle I've created an SQL Fiddle: http://sqlfiddle.com/#!2/a2c3f/2

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• When downloading a file using FileStream, why does page error message refers to aspx page name, not

  - by StuperUser

  After building a filepath (path, below) in a string (I am aware of Path in System.IO, but am using someone else's code and do not have the opportunity to refactor it to use Path). I am using a FileStream to deliver the file to the user (see below): FileStream myStream = new FileStream(path, FileMode.Open, FileAccess.Read); long fileSize = myStream.Length; byte[] Buffer = new byte[(int)fileSize + 1]; myStream.Read(Buffer, 0, (int)myStream.Length); myStream.Close(); Response.ContentType = "application/csv"; Response.AddHeader("content-disposition", "attachment; filename=" + filename); Response.BinaryWrite(Buffer); Response.Flush(); Response.End(); I have seen from: http://stackoverflow.com/questions/736301/asp-net-how-to-stream-file-to-user reasons to avoid use of Response.End() and Response.Close(). I have also seen several articles about different ways to transmit files and have diagnosed and found a solution to the problem (https and http headers) with a colleague. However, the error message that was being displayed was not about access to the file at path, but the aspx file. Edit: Error message is: Internet Explorer cannot download MyPage.aspx from server.domain.tld Internet Explorer was not able to open this Internet site. The requested site is either unavailable or cannot be found. Please try again later. (page name and address anonymised) Why is this? Is it due to the contents of the file coming from the HTTP response .Flush() method rather than a file being accessed at its address?

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• What is the proper way to code a read-while loop in Scala?

  - by ARKBAN

  What is the "proper" of writing the standard read-while loop in Scala? By proper I mean written in a Scala-like way as opposed to a Java-like way. Here is the code I have in Java: MessageDigest md = MessageDigest.getInstance( "MD5" ); InputStream input = new FileInputStream( "file" ); byte[] buffer = new byte[1024]; int readLen; while( ( readLen = input.read( buffer ) ) != -1 ) md.update( buffer, 0, readLen ); return md.digest(); Here is the code I have in Scala: val md = MessageDigest.getInstance( hashInfo.algorithm ) val input = new FileInputStream( "file" ) val buffer = new Array[ Byte ]( 1024 ) var readLen = 0 while( readLen != -1 ) { readLen = input.read( buffer ) if( readLen != -1 ) md.update( buffer, 0, readLen ) } md.digest The Scala code is correct and works, but feels very un-Scala-ish. For one it is a literal translation of the Java code, taking advantage of none of the advantages of Scala. Further it is actually longer than the Java code! I really feel like I'm missing something, but I can't figure out what. I'm fairly new to Scala, and so I'm asking the question to avoid falling into the pitfall of writing Java-style code in Scala. I'm more interested in the Scala way to solve this kind of problem than in any specific helper method that might be provided by the Scala API to hash a file. (I apologize in advance for my ad hoc Scala adjectives throughout this question.)

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• simplemodal - IE8 $.support.boxModel is not NULL and no object

  - by tom007

  Hi, I try to use the simplmodal script from: http://www.ericmmartin.com/projects/simplemodal/ I got this error $.support.boxModel is not NULL.. in IE8. jquery.simplemodal-1.3.4.min.js?F This is my implementation scipt.. what I have to change to avoid this error? function loadIframe(url){ $.modal('<iframe src="' + url + '" height="700px" width="600px" scrolling="no">', { containerCss:{ backgroundColor:"#fff", borderColor:"#333", }, overlayClose:true, opacity:70, overlayCss: { backgroundColor:"#000" }, onOpen: function (dialog) { dialog.overlay.fadeIn('slow', function () { dialog.container.toggleClass("preloader"); dialog.data.hide(); dialog.container.fadeIn('slow', function () { dialog.container.toggleClass("preloader"); dialog.data.slideDown('slow'); }); }); }, onClose: function (dialog) { dialog.data.fadeOut('slow', function () { dialog.container.slideUp('slow', function () { dialog.overlay.fadeOut('slow', function () { $.modal.close(); // must call this! }); }); }); } }); } $(document).ready(function(){ $("img").click(function(){ var baseurl = location.host; var url = $(this).attr("target"); var url = 'http://' + baseurl + url; loadIframe(url); }); });

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• what does this attempted trojan horse code do?

  - by bstullkid

  It looks like this just sends a ping, but whats the point of that when you can just use ping? /* WARNING: this is someone's attempt at writing a malware trojan. Do not compile and *definitely* don't install. I added an exit as the first line to avoid mishaps - msw */ int main (int argc, char *argv[]) { exit(1); unsigned int pid = 0; char buffer[2]; char *args[] = { "/bin/ping", "-c", "5", NULL, NULL }; if (argc != 2) return 0; args[3] = strdup(argv[1]); for (;;) { gets(buffer); /* FTW */ if (buffer[0] == 0x6e) break; switch (pid = fork()) { case -1: printf("Error Forking\n"); exit(255); case 0: execvp(args[0], args); exit(1); default: break; } } return 255; }

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• Can I specify default value?

  - by atch

  Why is it that for user defined types when creating an array of objects every element of this array is initialized with default ctor but when I create built-in type this isn't the case? And second question: is it possible to specify default value to be used while initialize? Something like this (not valid): char* p = new char[size]('\0'); And another question in this topic while I'm with arrays. I suppose that when creating an array of user defined type and knowing the fact that every elem. of this array will be initialized with default value firstly why? If arrays for built in types do not initialize their elems. with their dflts why do they do it for UDT, and secondly: is there a way to switch it off/avoid/circumvent somehow? It seems like bit of a waste if I for example have created an array with size 10000 and then 10000 times dflt ctor will be invoked and I will (later on) overwrite this values anyway. I think that behaviour should be consistent, so either every type of array should be initialized or none. And I think that the behaviour for built-in arrays is more appropriate.

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• how to use a parameterized function for the Default Binding of a Sql Server column

  - by Walt Gaber

  I have a table that catalogs selected files from multiple sources. I want to record whether a file is a duplicate of a previously cataloged file at the time the new file is cataloged. I have a column in my table (“primary_duplicate”) to record each entry as ‘P’ (primary) or ‘D’ (duplicate). I would like to provide a Default Binding for this column that would check for other occurrences of this file (i.e. name, length, timestamp) at the time the new file is being recorded. I have created a function that performs this check (see “GetPrimaryDuplicate” below). But I don’t know how to bind this function which requires three parameters to the table’s “primary_duplicate” column as its Default Binding. I would like to avoid using a trigger. I currently have a stored procedure used to insert new records that performs this check. But I would like to ensure that the flag is set correctly if an insert is performed outside of this stored procedure. How can I call this function with values from the row that is being inserted? USE [MyDatabase] GO SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE TABLE [dbo].[FileCatalog]( [id] [uniqueidentifier] NOT NULL, [catalog_timestamp] [datetime] NOT NULL, [primary_duplicate] nchar NOT NULL, [name] nvarchar NULL, [length] [bigint] NULL, [timestamp] [datetime] NULL ) ON [PRIMARY] GO ALTER TABLE [dbo].[FileCatalog] ADD CONSTRAINT [DF_FileCatalog_id] DEFAULT (newid()) FOR [id] GO ALTER TABLE [dbo].[FileCatalog] ADD CONSTRAINT [DF_FileCatalog_catalog_timestamp] DEFAULT (getdate()) FOR [catalog_timestamp] GO ALTER TABLE [dbo].[FileCatalog] ADD CONSTRAINT [DF_FileCatalog_primary_duplicate] DEFAULT (N'GetPrimaryDuplicate(name, length, timestamp)') FOR [primary_duplicate] GO USE [MyDatabase] GO SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE FUNCTION [dbo].[GetPrimaryDuplicate] ( @name nvarchar(255), @length bigint, @timestamp datetime ) RETURNS nchar(1) AS BEGIN DECLARE @c int SELECT @c = COUNT(*) FROM FileCatalog WHERE name=@name and length=@length and timestamp=@timestamp and primary_duplicate = 'P' IF @c > 0 RETURN 'D' -- Duplicate RETURN 'P' -- Primary END GO

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• C# Fun with Generics - Mutual Dependencies

  - by Kenneth Cochran

  As an experiment I'm trying to write a generic MVP framework. I started with: public interface IPresenter<TView> where TView: IView<IPresenter<... { TView View { get; set;} } public interface IView<TPresenter> where TPresenter:IPresenter<IView<... { TPresenter Presenter { get; set; } } Obviously this can't work because the types of TView and TPresenter can't be resolved. You'd be writing Type<Type<... forever. So my next attempt looked like this: public interface IView<T> where T:IPresenter { ... } public interface IView:IView<IPresenter> { } public interface IPresenter<TView> where TView: IView { ... } public interface IPresenter: IPresenter<IView> { ... } This actually compiles and you can even inherit from these interfaces like so: public class MyView : IView, IView<MyPresenter> { ... } public class MyPresenter : IPresenter, IPresenter<MyView> { ... } The problem is in the class definition you have to define any members declared in the generic type twice. Not ideal but it still compiles. The problem's start creeping up when you actually try to access the members of a Presenter from a View or vice versa. You get an Ambiguous reference when you try to compile. Is there any way to avoid this double implementation of a member when you inherit from both interfaces? Is it even possible to resolve two mutually dependent generic types at compile time?

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• C++: is it safe to work with std::vectors as if they were arrays?

  - by peoro

  I need to have a fixed-size array of elements and to call on them functions that require to know about how they're placed in memory, in particular: functions like glVertexPointer, that needs to know where the vertices are, how distant they are one from the other and so on. In my case vertices would be members of the elements to store. to get the index of an element within this array, I'd prefer to avoid having an index field within my elements, but would rather play with pointers arithmetic (ie: index of Element *x will be x - & array[0]) -- btw, this sounds dirty to me: is it good practice or should I do something else? Is it safe to use std::vector for this? Something makes me think that an std::array would be more appropriate but: Constructor and destructor for my structure will be rarely called: I don't mind about such overhead. I'm going to set the std::vector capacity to size I need (the size that would use for an std::array, thus won't take any overhead due to sporadic reallocation. I don't mind a little space overhead for std::vector's internal structure. I could use the ability to resize the vector (or better: to have a size chosen during setup), and I think there's no way to do this with std::array, since its size is a template parameter (that's too bad: I could do that even with an old C-like array, just dynamically allocating it on the heap). If std::vector is fine for my purpose I'd like to know into details if it will have some runtime overhead with respect to std::array (or to a plain C array): I know that it'll call the default constructor for any element once I increase its size (but I guess this won't cost anything if my data has got an empty default constructor?), same for destructor. Anything else?

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• UnicodeEncodeError: 'ascii' codec can't encode character [...]

  - by user1461135

  I have read the HOWTO on Unicode from the official docs and a full, very detailed article as well. Still I don't get it why it throws me this error. Here is what I attempt: I open an XML file that contains chars out of ASCII range (but inside allowed XML range). I do that with cfg = codecs.open(filename, encoding='utf-8, mode='r') which runs fine. Looking at the string with repr() also shows me a unicode string. Now I go ahead and read that with parseString(cfg.read().encode('utf-8'). Of course, my XML file starts with this: <?xml version="1.0" encoding="utf-8"?>. Although I suppose it is not relevant, I also defined utf-8 for my python script, but since I am not writing unicode characters directly in it, this should not apply here. Same for the following line: from __future__ import unicode_literals which also is right at the beginning. Next thing I pass the generated Object to my own class where I read tags into variables like this: xmldata.getElementsByTagName(tagName)[0].firstChild.data and assign it to a variable in my class. Now what perfectly works are those commands (obj is an instance of the class): for element in obj: print element And this command does work as well: print obj.__repr__() I defined __iter__() to just yield every variable while __repr__() uses the typical printf stuff: "%s" % self.varname Both commands print perfectly and can output the unicode character. What does not work is this: print obj And now I am stuck because this throws the dreaded UnicodeEncodeError: 'ascii' codec can't encode character u'\xfc' in position 47: So what am I missing? What am I doing wrong? I am looking for a general solution, I always want to handle strings as unicode, just to avoid any possible errors and write a compatible program. Edit: I also defined this: def __str__(self): return self.__repr__() def __unicode__(self): return self.__repr__() From documentation I got that this

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