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• Why is 'using namespace std;' considered a bad practice in C++?

  - by Mana

  Okay, sorry for the simplistic question, but this has been bugging me ever since I finished high school C++ last year. I've been told by others on numerous occasions that my teacher was wrong in saying that we should have "using namespace std;" in our programs, and that std::cout and std::cin are more proper. However, they would always be vague as to why this is a bad practice. So, I'm asking now: Why is "using namespace std;" considered bad? Is it really that inefficient, or risk declaring ambiguous vars(variables that share the same name as a function in std namespace) that much? Or does this impact program performance noticeably as you get into writing larger applications? I'm sorry if this is something I should have googled to solve; I figured it would be nice to have this question on here regardless in case anyone else was wondering.

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• How do you get 100% code coverage with guards in Haskell?

  - by dan_waterworth

  I'm trying to get (and prove) 100% test coverage for some code I'm writing in Haskell using HPC. However if I write something like this: fac n | n > 0 = n * (fac (n - 1)) | otherwise = 1 Then the second expression of the guard statement has always True tagged to it. What is the easiest way to overcome this in the general case? edit: Just to clarify. This code: fac n = if n > 0 then n * (fac (n - 1)) else 1 Works fine with HPC, (running it gives 100% code coverage). I'm basically suffering from this problem: http://hackage.haskell.org/trac/ghc/ticket/3175

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• Best data recovery tools?

  - by Nonick

  So due to a recent act of stupidity and bravado, I uttered the words "backups! who needs backups?!" and what followed was the tragic loss of 260gb of data. This scenario in particular is requiring me to recover a repartitioned hard disk, but I was wondering what tools people here use in general to recover lost data. I'm sure everyone has been there, either accidentally rewriting files, resaving an old version, computer crash, hard disk death, user deletes an important document etc. So was thinking it might be an interesting point of discussion as to what you guys use to recover lost data. I appologise if this is considered irrelevant, but considering there has been a few recovery questions, I think this might be interesting.

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• Find and sort by number of ocurrences of tag with Active Admin and act_as_taggable_on

  - by nunopolonia

  I'm using act_as_taggable_on and Active Admin on a Rails project. In that project there are Posts and each Post has Tags. I want to show a list of Tags in Active Admin and the number of ocurrences of each one. The way I found to do this was: index do column :name column :ocurrences do |tag| ocurrences = Post.tag_counts.find(tag.id).count end default_actions end Which will search the Tag List every time for every Post, which performance wise looks really bad. I would also like to be able to sort the tags by ocurrence. Any idea of how I can do it?

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• html - how do I make a page load in a new tab in IE8?

  - by erynion

  My website works in Firefox - pages on the site load in the current tab, and links off site load a new tab. IE8 won't behave: target="_blank" opens a whole new window; the other options, _self _top _parent, all open the page in the current tab. I have Firefox set to "Open new windows in a new tab." The links to pages on my site all have target="_self" and Firefox keeps these in the current tab. On the external links I don't have a target set (I added _blank to see if it fixed IE8, and doing that didn't affect Firefox). I can't find an equivalent setting in IE8. Tools-Internet Options-General-Tabs/Settings has an enable tabs box, and a sub-option to automatically switch to newly opened tabs. Is there some html that will work? An IE8 setting I'm missing? Any help appreciated.

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• How to deal with a coworker who keeps asking instead of searching herself?

  - by mafutrct

  I'm lucky enough to share a room with 3 other people at work. One of them, a senior programmer who's very talkative in general, tends to ask me various questions throughout the day. While some of them are surely ' legitimate', many questions could have been answered by putting in just slightly more search effort on their part. I really don't mind be asked stuff, and I can also cope with beginner questions, but this is seriously interrupting my flow. I clearly remember Joel talking about how private offices increase productivity because they prevent too easy questions from being asked. How should I deal with this situation? Getting a private office is out of the question, sadly. It's difficult to approach him directly, and he blissfully ignored the slight hints I tried to give.

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• Database design: one huge table or separate tables?

  - by littlegreen

  Currently I am designing a database for use in our company. We are using SQL Server 2008. The database will hold data gathered from several customers. The goal of the database is to acquire aggregate benchmark numbers over several customers. Recently, I have become worried with the fact that one table in particular will be getting very big. Each customer has approximately 20.000.000 rows of data, and there will soon be 30 customers in the database (if not more). A lot of queries will be done on this table. I am already noticing performance issues and users being temporarily locked out. My question, will we be able to handle this table in the future, or is it better to split this table up into smaller tables for each customer?

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• public (static) swap() method vs. redundant (non-static) private ones...

  - by Helper Method

  I'm revisiting data structures and algorithms to refresh my knowledge and from time to time I stumble across this problem: Often, several data structures do need to swap some elements on the underlying array. So I implement the swap() method in ADT1, ADT2 as a private non-static method. The good thing is, being a private method I don't need to check on the parameters, the bad thing is redundancy. But if I put the swap() method in a helper class as a public static method, I need to check the indices every time for validity, making the swap call very unefficient when many swaps are done. So what should I do? Neglect the performance degragation, or write small but redundant code?

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• iPhone "multi-threading" question

  - by MrDatabase

  I have a simple iPhone game consisting of two "threads": the main game loop where all updating and rendering happen 30 times per second (NSTimer)... and the "thread" that calls the accelerometer delegate 100 times per second. I have a variable "xPosition" that's updated in the accelerometer delegate function and used in the game loop. Is there a possibility of the two "threads" trying to use xPosition at the same time (hence causing a crash or some other problem). If so how can I fix this w/ minimal impact to the game's performance? I've been using this set-up for many months of development and incremental testing and I've never run into any problems. Cheers!

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• How does ‘Servers’ view work underlying in Eclipse?

  - by Michael Lu

  ‘Servers’ is built-in view in Eclipse. We could integrate jee server into Eclipse easily. It could start/stop server both in normal and debug modes. Moreover, we could even set timeout and deployment path, things like that. Various types of server tomcat, jboss, websphere are supported, no intrusive to server. I am just curious about how these cool things happen behind the scene. The complete mechanism is large and complex, so I just want to know general mechanism about it, an article also could be fine for me. Thank you!

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• NSCurrentLocaleDidChangeNotification on iPhone OS

  - by 0xced

  While the NSCurrentLocaleDidChangeNotification perfectly makes sense on Mac OS X, I don't see how you can possibly receive it on iPhone OS. In order to change the locale, you have to quit the running application, then change it in Settings ? General ? International ? Region Format. At that point, your app is not running, so how could it receive the notification? I first thought this notification was leftover from the Mac OS X documentation, but then I found this in Apple Push Notification Service Programming Guide: The application might send its provider the preferred language every time the user changes something in the current locale. To do this, you can listen for the notification named NSCurrentLocaleDidChangeNotification and, in your notification-handling method, get the code identifying the preferred language and send that to your provider. So, how do you trigger this notification on iPhone OS?

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• how can I open eclipse and see the project view I last looked at?

  - by Stato Machino

  I'm completely mystified. I do not understand why Eclipse does not show me my list of projects! And all the answers I've seen to similar questions do not mention any 'go here and do that' type of answers. I tried 'Import/General/Existing Projects into Workspace/browse-to...' but that told me the project was already in the workspace. But I KNEW THAT! The project menu does not have an 'open project' option!!!! There is no 'open workspace' option. How do people open Eclipse and 'resume working'??? What is the single, dependable, repeatable option for opening the 'project tree' to show my project? [or tell me my expectations that Java people are smarter are way off base!] Thanks, Kimball

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• Is it possible to use the values method for a HashMap if the values are ArrayLists?

  - by Denman

  I'm stuck trying to get something to work in an assignment. I have a HashMap<Integer, ArrayList<Object>> called sharedLocks and I want to check whether a certain value can be found in any ArrayList in the HashMap. The following code obviously wouldn't work because Object[] can't be cast to ArrayList[], but it is a demonstration of the general functionality that I want. ArrayList[] values = (ArrayList[]) sharedLocks.values().toArray(); boolean valueExists = false; for (int i = 0; i < values.length; i++) { if (values[i].contains(accessedObject)) { valueExists = true; } } Is there a way for me to check every ArrayList in the HashMap for a certain value? I'm not sure how to use the values method for HashMaps in this case. Any help would be much appreciated.

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• Best way to have unique key over 500M varchar(255) records in mysql/innodb?

  - by taw

  I have url column with unique key over it - but its performance on updates is absolutely atrocious. I suspect that's because the index doesn't all fit in memory. So I was thinking, how about adding a column of md5(url) with 16 bytes of binary data and unique-keying that instead. What would be the best datatype for that? I'd love to be able to just see 32-character hex hash, while mysql would convert it to/from 16 binary bytes and index that, as programs using the database might have some troubles with arbitrary binary data that I'd rather avoid if possible (also I'm a bit afraid that mysql might get some strange ideas about character sets and for example overalocating storage for that by 3:1 because it thinks it might need utf8, how do I avoid that for cure?).

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• How to generate JSON object on client side and send it to server?

  - by EugeneS

  I have ExtJS based application. I have compound object on the server side, and have ExtJS window with few tabs for editing different parts of this one object. For example: I Have Compound object "Car" public class Car { public string Name; public string Color; public List Wheels; public List Doors; } And on my ExtJS window i have tabs ("General Info", "Wheels", "Doors") for editing different parts of this object. So what i want: When i want to create a new car i want to generate JSON configuration for my class "Car" like {Name:null; Color:null; Wheels:[]; Doors:[]} then sent it to the client, fill it on the client (without callbacks to server) and after user finishes creating his Car object (he added wheels, doors, set name and color) and press save, I want to sent this filled(generated) JSON object to server and save it to DB. Is it possible? Thanks

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• Dividing n-bit binary integers

  - by Julian

  Was wondering if anyone could help me with creating a pseudocode for how to go about dividing n-bit binary integers. Here is what I'm thinking could possibly work right now, could someone correct this if I'm wrong: divide (x,y) if x=0: return (0,0) //(quotient, remainder) (q,r) = divide(floor(x/2), y) q=2q, r=2r if x is odd: r = r+1 if r >= y: r = r-y, q = q+1 return (q,r) Would you guys say that this general pseudocode algorithm would accomplish the intended task of dividing n-bit numbers or am I missing something in my psuedocode before I start coding up something that's wrong?

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• MATLAB pdist function

  - by James

  Hi, I am using the pdist command to find the distance between x and y coordinates stored in a matrix. X = [100 100; 0 100; 100 0; 500 400; 300 600;]; D = pdist(X,'euclidean') Which returns a 15 element vector. : [0.734979755525412 3.40039811339820 2.93175207511321 1.83879677592575 2.40127440268306 2.75251513299386 2.21488402640753 1.10610649500317 1.81674017301699 0.903207751535635 1.99116952754924 1.05069952386082 1.24122819418333 1.08583377275532 1.38729428638035] Is there a way to associate these distances with the coordinates they were derived from, i.e. store them in a matrix with the general row form: [Length xcoordinate1 ycoordinate1 xcoordinate2 ycoordinate2] Where there is a row for each length found? Thanks in advance

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• "Volkswagen Passat" Navigation

  - by joe_midi

  http://web.vw.com/all-new-passat-experience/ The navigation on this .swf is very impressive, and I was wondering how I would go about replicating it. The way each of the sections Design / Technology / Safety / Performance I want to know how each section can expand and still fit together. I've started with MOUSE_OVER events, but I'm not entirely sure how to order them so each section is the right size for every mouse over Event. This is the code I have for each "Section", I have created a movie clip with a Mask that expands on mouse over and brings the selected clip to the highest depth. this.firstButton01.addEventListener(MouseEvent.MOUSE_OVER, firstButton01OVER) function firstButton01OVER(e:Event):void { this.firstButton01.gotoAndPlay(2); this.setChildIndex(firstButton01,this.numChildren-1); }

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• Two part form in Rails

  - by samuel02

  I have some two nested resources, so that a Product can have many Bookings. On one page in a different controller I want to create a new booking and since it's a "general" booking I want a select menu to appear in a modal window where the user is able to pick one of the existing products and then go to the booking page. How can I do this? I have no problem setting up the modal and the "New booking" page is already there. What I need is a form that generates a list of existing products, picks the selected product id and then gets /products/:product_id/bookings/new . Any help appreciated! I realize my title does not describe my problem very good so better suggestions are highly welcome!

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• specyfic syntax question

  - by bua

  Hi there, Is it possible to create template to the initialization like: template <typename C> typename C::value_type fooFunction(C& c) {...}; std::vector<string> vec_instance; fooFunction(cont<0>(vec_instance)); fooFunction(cont<1>(vec_instance)); In general i'm interested is it possible to specify template using integer (ie. 0) instead of true type name. And how to achieve above?

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• Java : VolatileImage slower than BufferedImage.

  - by Norswap

  I'm making a game in java and in used BufferedImages to render content to the screen. I had performance issues on low end machines where the game is supposed to run, so I switched to VolatileImage which are normally faster. Except they actually slow the whole thing down. The images are created with GraphicsConfiguration.createCompatibleVolatileImage(...) and are drawn to the screen with Graphics.drawImage(...) (follow link to see which one specifically). They are drawn upon a Canvas using double buffering. Does someone has an idea of what is going wrong here ?

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• Any good class diagram editors out there for Java (not UML)

  - by user85116

  I'm looking for an editor that can create class diagrams, similar to the typical UML class diagram, but specifically for java (so using java terminology; instead of terms like "generalization, realization etc", we use the java equivalents "interface, abstract class, extends etc"). I've looked into UML several times, but each time I've been turned off by the shear amount of "stuff" that comes with UML. I just want to be able to model my java classes quickly and intuitively, without getting bogged down by all the cruft that comes with UML. Preferably, it would come with a source reader that can keep the diagram up to date, and with a few nice features like "show only public methods in this class" etc. As well, it would automatically "know" about the classes in the standard java library, and possibly even be able to read classes from jars. Performance is also a big thing for me, I don't like having to wait 2 seconds for a popup menu to appear, or watch the diagram jerk crazily while resizing an element in the model. What do you think, am I asking too much?

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• What is the difference between these two ways of creating NSStrings?

  - by adame

  NSString *myString = @"Hello"; NSString *myString = [NSString stringWithString:@"Hello"]; I understand that using method (1) creates a pointer to a string literal that is defined as static memory (and cannot be deallocated) and that using (2) creates an NSString object that will be autoreleased. Is using method (1) bad? What are the major differences? Is there any instances where you would want to use (1)? Is there a performance difference? P.S. I have searched extensively on Stack Overflow and while there are questions on the same topic, none of them have answers to the questions I have posted above.

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• Hudson's FindBugs plugin reports line number "-1" for bugs. Ideas?

  - by John B.

  Greetings, I have a simple test project set up in Hudson and the project's build process (a batch file) generates a findbugs.xml file. This is processed by Hudson's FindBugs plugin but it shows the line number of the bugs as "-1" instead of their actual line number. A coworker suggested I enable debug info for the compiler. I used the -g "Generate all debugging info" option for javac but nothing seemed to change. My build command is: javac -g -classpath C:\testWebApp1\src -d C:\testWebApp1\build C:\testWebApp1\src\*.java The only other thing in the build.bat file is a call to the FindBug tool (text UI). Here is what the FindBugs Plugin says about the first bug: File: GenerateHellos.java, Line: -1, Type: UUF_UNUSED_FIELD, Priority: Normal, Category: PERFORMANCE Any ideas? Thanks a ton!

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• Simulators for thread scheduling on multicore

  - by shijie xu

  I am seeking a simulator for thread scheduling at multi-core architecture, that is mapping threads to the cores at runtime. During runtime, simulator collects overall cache and IPC statistics. I checked below simulators, but seems there are not sufficient for me: Simplescalar: A simulator only for single core. SESC: multiprocessor simulator with detailed power, thermal, and performance models, QSim: provides instruction-level control of the emulated environment and detailed information about the executing instruction stream. It seems both SESC and QSim supports instructions scheduling instead of thread scheduling on the cores? Anyone can help provide some clues or share experience for this part?

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