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• How do I create "undo" in c++?

  - by b3y4z1d

  I've got a couple of codes to do some things but I need to create a function that undoes the previous task/addition/change.How do I do this in Borland C++? (the program stores strings of text in a text file using "list",it is stored and then erased unless I use the save-function I've created) right,so I don't know if I've forgotten to mention anything of importance for you to be able to help me better,but if there's something you're wondering about the functions just ask. I meant creating an undo function in a simple consol application by the way.

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• Should every class have its own namespace?

  - by thehouse

  Something that has been troubling me for a while: The current wisdom is that types should be kept in a namespace that only contains functions which are part of the type's non-member interface (see C++ Coding Standards Sutter and Alexandrescu or here) to prevent ADL pulling in unrelated definitions. Does this imply that all classes must have a namespace of their own? If we assume that a class may be augmented in the future by the addition of non-member functions, then it can never be safe to put two types in the same namespace as either one of them may introduce non-member functions that could interfere with the other. The reason I ask is that namespaces are becoming cumbersome for me. I'm writing a header-only library and I find myself using classes names such as project::component::class_name::class_name. Their implementations call helper functions but as these can't be in the same namespace they also have to be fully qualified!

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• Two parameters in asp.net mvc route

  - by olst

  Hi. This is a modification to a question I've asked before on this forum. My controller action: public ActionResult SearchResults(string searchTerm, int page)... My view: <%= Html.PageLinks((int)ViewData["CurrentPage"], (int)ViewData["TotalPages"], i => Url.Action("SearchResults", new { page = i }))%>... The route entries: routes.MapRoute( null, "SearchResults", new { controller = "Search", action = "SearchResults", page = 1 } // Defaults ); routes.MapRoute( "Search", "SearchResults/Page{page}", new { controller = "Search", action = "SearchResults" }, new { page = @"\d+" } ); My goal is to have paging links for the search results. The problem is that when I click any page in the paging links, it gives me the search results of an empty serach term. How can I pass the search term parameter which is a string in addition to the page number parameter ? What should I put in the routing ?

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• C# is there a problem with division?

  - by Tom

  This is a piece of my code, it is called every second, after about 10 seconds the values start to become weird (see below): double a; double b; for (int i = 0; i < currAC.Length; i++ ) { a = currAC[i]; b = aveACValues[i]; divisor = (a/b); Console.WriteLine("a = " + a.ToString("N2") + "\t" + "b = " + b.ToString("N2")); Console.WriteLine("divisor = " + divisor); Console.WriteLine("a+b = " + (a+b)); } and the output: a = -0.05 b = 0.00 divisor = 41 a+b = -0.0524010372273268 currAC and aveACValues are double[] what on earth is going on???? The addition result is correct every time, but the division value is wrong, yet it is reading a and b correctly?? EDIT: '41' is the value of the first calculation, ie when a = currAC[0], but this should not remain???

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• R.matlab/readMat : Error in readTag(this)

  - by Megan

  I am trying to read a matlab file into R using R.matlab but am encountering this error: require(R.matlab) r <- readMat("file.mat", verbose=T) Trying to read MAT v5 file stream... Error in readTag(this) : Unknown data type. Not in range [1,19]: 18569 In addition: Warning message: In readMat5Header(this, firstFourBytes = firstFourBytes) : Unknown MAT version tag: 512. Will assume version 5. How can this issue be solved or is there an alternative way to load matlab files? I can use hdf5load but have heard this can mess with the data. Thanks!

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• What time function do I need to use with pthread_cond_timedwait?

  - by Vincent

  The pthread_cond_timedwait function needs an absolute time in a time timespec structure. What time function I'm suppose to use to obtain the absolute time. I saw a lot of example on the web and I found almost all time function used. (ftime, clock, gettimeofday, clock_gettime (with all possible CLOCK_...). The pthread_cond_timedwait uses an absolute time. Will this waiting time affected by changing the time of the machine? Also if I get the absolute time with one of the time function, if the time of the machine change between the get and the addition of the delta time this will affect the affect the wait time? Is there a possibility to wait for an event with a relative time instead?

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• When designing an event, is it a good idea to prevent listeners from being added twice?

  - by Matt

  I am creating an event-based API where a user can subscribe to an event by adding listener objects (as is common in Java or C#). When the event is raised, all subscribed listeners are invoked with the event information. I initially decided to prevent adding an event listener more than once. If a listener is added that already exists in the listener collection, it is not added again. However, after thinking about it some more, it doesn't seem that most event-based structures actually prevent this. Was my initial instinct wrong? I'm not sure which way to go here. I guess I thought that preventing addition of an existing listener would help to avoid a common programming error. Then again, it could also hide a bug that would lead to code being run multiple times when it shouldn't.

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• Why Use java.lang.reflect.Array For Anything Other Than Array Creation?

  - by dimo414

  Java Class java.lang.reflect.Array provides a set of tools for creating an array dynamically. However in addition to that it has a whole set of methods for accessing (get, set, and length) an array. I don't understand the point of this, since you can (and presumably would) cast your dynamically generated array as an array upon creation, which means you can use the normal array access (bracket notation) functionality. In fact, looking at the source code you can see that is all the class does, cast the array, and throw an exception if the cast fails. So what's the point / usefulness of all of these extra methods?

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• Confused by "let" in Clojure

  - by Tom Dalling

  I just started playing with Clojure, and I wrote a small script to help me understand some of the functions. It begins like this: (def *exprs-to-test* [ "(filter #(< % 3) '(1 2 3 4 3 2 1))" "(remove #(< % 3) '(1 2 3 4 3 2 1))" "(distinct '(1 2 3 4 3 2 1))" ]) Then it goes through *exprs-to-test*, evaluates them all, and prints the output like this: (doseq [exstr *exprs-to-test*] (do (println "===" (first (read-string exstr)) "=========================") (println "Code: " exstr) (println "Eval: " (eval (read-string exstr))) ) ) The above code is all working fine. However, (read-string exstr) is repeated so I tried to use let to eliminate the repetition like so: (doseq [exstr *exprs-to-test*] (let [ex (read-string exstr)] ( (do (println "===" (first ex) "=========================") (println "Code: " exstr) (println "Eval: " (eval ex)) ) )) ) But this works once for the first item in *exprs-to-test*, then crashes with a NullPointerException. Why is the addition of let causing the crash?

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• Cannot see index view of my controller - routing related

  - by olst

  Hi. I have a controller named Content, which has an Index action, which is associated with a view. I would like the simple route "content" to show me the index view of the content controller, so I use the following code (with the addition of the default site home route): routes.MapRoute( "ContentIndex", "content", new { controller = "Content", action = "Index"} ); routes.MapRoute( "Default", "{controller}/{action}", new { controller = "Home", action = "Index" } ); when I type the url : "http://localhost/content/", I get an error 404 saying the resource cannot be found, but when I type "http://localhost/content/index", it shows the content index view. How can I get rid of the index in the url ? Thanks !

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• Hashing a python function to regenerate output when the function is modified

  - by Seth Johnson

  I have a python function that has a deterministic result. It takes a long time to run and generates a large output: def time_consuming_function(): # lots_of_computing_time to come up with the_result return the_result I modify time_consuming_function from time to time, but I would like to avoid having it run again while it's unchanged. [time_consuming_function only depends on functions that are immutable for the purposes considered here; i.e. it might have functions from Python libraries but not from other pieces of my code that I'd change.] The solution that suggests itself to me is to cache the output and also cache some "hash" of the function. If the hash changes, the function will have been modified, and we have to re-generate the output. Is this possible or ridiculous? Updated: based on the answers, it looks like what I want to do is to "memoize" time_consuming_function, except instead of (or in addition to) arguments passed into an invariant function, I want to account for a function that itself will change.

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• Combining XmlSerializer and XmlWriter?

  - by num3ric

  In addition to a list of objects I am serializing to an xml file using C#'s XmlSerializer, I would like to store a few more independent elements (mainly strings from textboxes) in the same xml. public static void SaveBehaviors(ObservableCollection<Param> listParams) { XmlSerializer _paramsSerializer = new XmlSerializer(listParams.GetType()); string path = Environment.GetFolderPath(Environment.SpecialFolder.Desktop); path += "\\test.xml"; using (TextWriter writeFileStream = new StreamWriter(path)) { _paramsSerializer.Serialize(writeFileStream, listParams); using (XmlWriter writer = XmlWriter.Create(writeFileStream)) { writer.WriteStartElement("Foo"); //test entry... writer.WriteAttributeString("Bar", "Some & value"); writer.WriteElementString("Nested", "data"); writer.WriteEndElement(); } } } However, deserializing "test.xml" results in an error because of the added element. I suppose writing in the serialized xml file is prohibited and should be avoided?

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• lwjgl isKeyDown canceling out other keys

  - by AKrush95

  While trying to create a simple game where a square is manipulated via the keyboard keys, I have come across a small, rather irritating problem. I would like it to work so that when the opposite directional key is pressed, the character will stop; the character may move the other two directions while stopped in this situation. This works perfectly with LEFT and RIGHT held down; the player may move UP or DOWN. If UP and DOWN are held down, however, the player will not move, nor will Java recognize that the LEFT or RIGHT keys were pressed. import java.util.ArrayList; import java.util.Random; import org.lwjgl.*; import org.lwjgl.input.Keyboard; import org.lwjgl.opengl.*; import static org.lwjgl.opengl.GL11.*; public class Main { private Man p; private ArrayList<Integer> keysDown, keysUp; public Main() { try { Display.setDisplayMode(new DisplayMode(640, 480)); Display.setTitle("LWJGLHelloWorld"); Display.create(); } catch (LWJGLException e) { e.printStackTrace(); } p = new Man(0, 0); keysDown = new ArrayList<>(); keysUp = new ArrayList<>(); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho(0, 640, 480, 0, 1, -1); glMatrixMode(GL_MODELVIEW); while (!Display.isCloseRequested()) { glClear(GL_COLOR_BUFFER_BIT); checkKeys(); p.draw(); Display.update(); Display.sync(60); } Display.destroy(); } public void checkKeys() { ArrayList<Integer> keys = new ArrayList<>(); keys.add(Keyboard.KEY_A); keys.add(Keyboard.KEY_D); keys.add(Keyboard.KEY_W); keys.add(Keyboard.KEY_S); for (int key : keys) { if (Keyboard.isKeyDown(key)) keysDown.add(key); else keysUp.add(key); } keysDown.removeAll(keysUp); keysUp = new ArrayList<>(); int speed = 4; int dx = 0; int dy = 0; if (keysDown.contains(keys.get(2))) { System.out.println("keyUP"); dy -= speed; } if (keysDown.contains(keys.get(3))) { System.out.println("keyDOWN"); dy += speed; } if (keysDown.contains(keys.get(0))) { System.out.println("keyLEFT"); dx -= speed; } if (keysDown.contains(keys.get(1))) { System.out.println("keyRIGHT"); dx += speed; } //if (keysDown.contains(keys.get(0)) && keysDown.contains(keys.get(1))) dx = 0; //if (keysDown.contains(keys.get(2)) && keysDown.contains(keys.get(3))) dy = 0; p.update(dx, dy); } public static void main(String[] args) { new Main(); } class Man { public int x, y, w, h; public float cR, cG, cB; public Man(int x, int y) { this.x = x; this.y = y; w = 50; h = 50; Random rand = new Random(); cR = rand.nextFloat(); cG = rand.nextFloat(); cB = rand.nextFloat(); } public void draw() { glColor3f(cR, cG, cB); glRecti(x, y, x+w, y+h); } public void update(int dx, int dy) { x += dx; y += dy; } } } That is the code that I am working with. In addition, I am unsure how to compile an executable jar that is using the lwjgl library in addition to slick-util.

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• jQuery sanitizing comments and linkifying URLs

  - by iWasRobbed

  In terms of jQuery (or Javascript), what happens behind the scenes when a person posts a comment on Facebook, Twitter, or a blog? For instance, do they sanitize the text first, and then pattern match URL's into an actual link? Are there other items of concern that the client-side should check in addition to doing some checks on the backend? I have found a few regex's for turning URL's into links, but I'm not sure if there are better solutions. I'm trying to wrap my head around the problem, but I'm having a difficult time knowing where to start. Any guidance you can provide is greatly appreciated!

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• Recover a deleted webpage

  - by rc

  Suppose, a blog or a nice article was hosted on a website and it got deleted or worse the website was brought down. How do you view that web page? I tried searching for the cached version in Google. But, looks like the content was deleted long ago and is not listed in the search results directly. There are annotations to the link from many other sites, but still the actual content is not fully available. Now, can anybody help me see this page... I am actually looking for http://effectize.com/become-coolest-programmer :) And, moreover, in addition to bookmarking a favorite link, is it possible to cache the content of the link as well for later reference in case it gets deleted? EDIT: Looks like a URL can be cached for future reference. Try: http://backupurl.com/

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• Separate Datasource for Gridview Footer

  - by Mike Keller

  I need to able to display the results from a seperate query in the footer of a gridview. What is the best way to go about this? I did some google searches and what I found pretty much revolves using the original datasource and doing something like addition to display the information in the footer. However I really need to be able to display this single line of information from a seperate query. Any direction given would be appreciated. Links, tips, tricks, etc. Thanks.

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• Sorting array of 1000 distinct integers in the range [1, 5000], accessing each element at most once

  - by Cronydevil

  Suppose you have an array of 1000 integers. The integers are in random order, but you know each of the integers is between 1 and 5000 (inclusive). In addition, each number appears only once in the array. Assume that you can access each element of the array only once. Describe an algorithm to sort it. How i can sorting? If you used auxiliary storage in your algorithm, can you find an algorithm that remains O(n) space complexity?

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• using helper methods in a view in rails 3

  - by Frida777

  Hello everyone, there is something that is disturbing me a bit about rails 3. i am trying to upgrade my application from rails 2 to rails 3. i followed all the steps necessary to do and things were working well for me till now except one thing: i have a helper method that is defined differently in different helpers, for example it is defined in the application_helper in one way and the same method defined in a different way in the homepage_helper, and defined differently in another helper, let's say video_helper, in addition to that, it is used in a shared view that is used throughout the application, now if i am in the homepage, i want this function to get called from the homepage_helper and if i am in the video page, the function must be called from the video_helper, based on the concept of convention in rails, this worked perfectly in rails 2 but in rails 3, the function is always called from the last helper, alphabetically ordered, that is in the example, video_helper. How can i fix this? Kindly advice. Appreciate all the help.

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• View / ViewModel - what is the sense (in a WPF control)?

  - by TomTom

  Not as funny as it sounds. Normally the View / ViewModel should decouple the presentation from the business logic. Good. Now, a Control in WPF is basically invisible unless made different (with the exceptions of UserControl and Window that have XAML directly attached). The Style is putting in the "visual presentation" - which basically means a Control does not need a view mechanism as WPF already has one? In addition. the ViewModel is actually part of the Control, or? Just fighting with that stuff. I know in ASP.NET, WinForms the separation makes a lot of sense - but there, basically, controls HAVE an intrinsic look. In WPF, I have some where it makes sense (derived from UserControl), but for the majority of the controls I write, the View & ViewModel look like pretty much totally superflous thanks to the already presenting view mechanism.

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• How to implement nested SQL transactions with ADO.NET?

  - by manza_jurjur

  I need to implement nested transactions in .NET using ADO.NET. The situation is as follows: --> Start Process (Begin Transaction) --> Begin Transaction for step 1 --> Step 1 --> Commit transaction for step 1 --> Begin transaction for step 2 --> Step 2 --> Rollback transaction for step 2 --> etc ... --> End Process (Commit or Rollback ALL commited steps) Can that be done with transaction scopes? Could anyone post an example? In addition I'd need the prcoess to work for SQL Server 2005 AND Oracle 10g databases... will transaction scopes work with both database engines?

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• What is the best software to write and organize written copy / content for a website?

  - by johnqtaxpayer

  I'm a newbie product manager, looking for tips on how to write and organize text copy for my company's website. I need to be able to prepare the content for our public site and turn it over to the web designer who publishes it to our live site. I want our UI team to be able to quickly glance at the copy I write and immediately know where on the page I intend for it to go. Currently, I'm using microsoft word to write and color code different text to signify where I want specific text to go. It is difficult for the UI guy to immediately know if something goes into the nav bar or into a header or a description below a header. In addition to that, it would be helpful for me to be able to write the copy in such a way that the web designer could copy and paste it into the XHTML without having to go back and manually replace special punctuation characters with the XHTML entities. What software is out there that will allow a comprehensive solution to these web copywriting issues?

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• [php + mysql] Save IP in database

  - by Knarf

  When a user logs inn I want to save their IP in the database. How would I do that? What type is best to use for the MySQL field? How would the PHP code to get IP look like? I'm thinking of using it as an extra security feature for the login/session stuff. I'm thinking of checking the IP the user logged in with from the DB with the IP the user have now as addition to checking the session. So that it first check the session, and then check if you have a valid IP. Is that an allright extra feature? And what other things can I do to make it more secure?

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• In Perl, can I limit the length of a line as I read it in from a file (like fgets)

  - by SB

  I'm trying to write a piece of code that reads a file line by line and stores each line, up to a certain amount of input data. I want to guard against the end-user being evil and putting something like a gig of data on one line in addition to guarding against sucking in an abnormally large file. Doing $str = <FILE> will still read in a whole line, and that could be very long and blow up my memory. fgets lets me do this by letting me specify a number of bytes to read during each call and essentially letting me split one long line into my max length. Is there a similar way to do this in perl? I saw something about sv_gets but am not sure how to use it (though I only did a cursory Google search). Thanks.

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• How can I use an array within a SQL query

  - by ThinkingInBits

  So I'm trying to take a search string (could be any number of words) and turn each value into a list to use in the following IN statement) in addition, I need a count of all these values to use with my having count filter $search_array = explode(" ",$this->search_string); $tag_count = count($search_array); $db = Connect::connect(); $query = "select p.id from photographs p left join photograph_tags c on p.id = c.photograph_id and c.value IN ($search_array) group by p.id having count(c.value) >= $tag_count"; This currently returns no results, any ideas?

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• Should I still use querystrings for page number, etc, when using ASP.NET 4 URL Routing?

  - by Scott

  I am switching from Intelligencia's UrlRewriter to the new web forms routing in ASP.NET 4.0. I have it working great for basic pages, however, in my e-commerce site, when browsing category pages, I previously used querystrings that were built into my pager control to control paging. An old url (with UrlRewriting) would be: http://www.mysite.com/Category/Arts-and-Crafts_17 I now have a MapPageRoute defined in global.asax as: routes.MapPageRoute("category-browse", "Category/{name}_{id}", ~/CategoryPage.aspx"); This works great. Now, somebody clicks to go to page 2. Previously I would have just tacked on ?page=2 as the querystring. Now, How do I handle this using web forms routing? I know I can do something like: http://www.mysite.com/Category/Arts-and-Crafts_17/page/2 But in addition to page, I can have filters, age ranges, gender, etc. Should I just keep defining routes that handle these variables, or should I continue using querystrings and can I define a route that allows me to use my querstrings like before?

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