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• Difference between float and double

  - by VaioIsBorn

  I know, i've read about the difference between double precision and single precision etc. But they should give the same results on most cases right ? I was solving a problem on a programming contest and there were calculations with floating point numbers that were not really big so i decided to use float instead of double, and i checked it - i was getting the correct results. But when i send the solution, it said only 1 of 10 tests was correct. I checked again and again, until i found that using float is not the same using double. I put double for the calculations and double for the output, and the program gave the SAME results, but this time it passed all the 10 tests correctly. I repeat, the output was the SAME, the results were the SAME, but putting float didn't work - only double. The values were not so big too, and the program gave the same results on the same tests both with float and double, but the online judge accepted only the double-provided solution. Why ? What is the difference ?

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• pdf external streams in Max OS X Preview

  - by olpa

  According to the specification, a part of a PDF document can reside in an external file. An example for an image: 2 0 obj << /Type /XObject /Subtype /Image /Width 117 /Height 117 /BitsPerComponent 8 /Length 0 /ColorSpace /DeviceRGB /FFilter /DCTDecode /F (pinguine.jpg) >> stream endstream endobj I found that this functionality does work in Adobe Acrobat 5.0 for Windows (sample PDF with the image), also I managed to view this file in Adobe Acrobat Reader 8.1.3 for Mac OS X after I found the setting "Allow external content". Unfortunately, it seems that non-Adobe tools ignore the external stream feature. I hope I'm wrong, therefore ask the question: How to enable external streams in Mac OS X? (I think that all the system Mac OS X tools use the same library, therefore say "Mac OS X" instead of "Preview".) Or maybe there could be a programming hook to emulate external streams? My task is: store a big set of images (total ˜300Mb) outside of a small PDF (˜1Mb). At some moment, I want to filter PDF through a quartz filter and get a PDF with the images embedded. Any suggestions are welcome.

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• How to update GUI thread/class from worker thread/class?

  - by user315182

  First question here so hello everyone. The requirement I'm working on is a small test application that communicates with an external device over a serial port. The communication can take a long time, and the device can return all sorts of errors. The device is nicely abstracted in its own class that the GUI thread starts to run in its own thread and has the usual open/close/read data/write data basic functions. The GUI is also pretty simple - choose COM port, open, close, show data read or errors from device, allow modification and write back etc. The question is simply how to update the GUI from the device class? There are several distinct types of data the device deals with so I need a relatively generic bridge between the GUI form/thread class and the working device class/thread. In the GUI to device direction everything works fine with [Begin]Invoke calls for open/close/read/write etc. on various GUI generated events. I've read the thread here (How to update GUI from another thread in C#?) where the assumption is made that the GUI and worker thread are in the same class. Google searches throw up how to create a delegate or how to create the classic background worker but that's not at all what I need, although they may be part of the solution. So, is there a simple but generic structure that can be used? My level of C# is moderate and I've been programming all my working life, given a clue I'll figure it out (and post back)... Thanks in advance for any help.

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• Endianness and C API's: Specifically OpenSSL.

  - by Hassan Syed

  I have an algorithm that uses the following OpenSSL calls: HMAC_update() / HMAC_final() // ripe160 EVP_CipherUpdate() / EVP_CipherFinal() // cbc_blowfish These algorithm take a unsigned char * into the "plain text". My input data is comes from a C++ std::string::c_str() which originate from a protocol buffer object as a encoded UTF-8 string. UTF-8 strings are meant to be endian neutrial. However I'm a bit paranoid about how OpenSSL may perform operations on the data. My understanding is that encryption algorithms work on 8-bit blocks of data, and if a unsigned char * is used for pointer arithmetic when the operations are performed the algorithms should be endian neutral and I do not need to worry about anything. My uncertainty is compounded by the fact that I am working on a little-endian machine and have never done any real cross-architecture programming. My beliefs/reasoning are/is based on the following two properties std::string (not wstring) internally uses a 8-bit ptr and a the resulting c_str() ptr will itterate the same way regardless of the CPU architecture. Encryption algorithms are either by design, or by implementation, endian neutral. I know the best way to get a definitive answer is to use QEMU and do some cross-platform unit tests (which I plan to do). My question is a request for comments on my reasoning, and perhaps will assist other programmers when faced with similar problems.

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• iPhone OpenGL ES Texture2D Masking

  - by Robert Neagu

  What's the best choice when trying to mask a texture like ColorSplash or other apps like iSteam, etc? I started learning OPENGL ES like... 4 days ago (I'm a total rookie) and tried the following approach: 1) I created a colored texture2D, a grayscale version of the first texture and a third texture2D called mask 2) I also created a texture2D for the brush... which is grayscale and it's opaque (brush = black = 0,0,0,1 and surroundings = white = 1,1,1,1). My intention was to create an antialiased brush with smooth edges but i'm fine with a normal one right now 3) I searched for masking techniques on the internet and found this tutorial ZeusCMD - Design and Development Tutorials : OpenGL ES Programming Tutorials - Masking about masking. The tutorial tells me to use blending to achieve masking... first draw colored, then mask with glBlendFunc(GL_DST_COLOR, GL_ZERO) and then grayscale with glBlendFunc(GL_ONE, GL_ONE) ... and this gives me something close to what i want... but not exactly what i want. The result is masked but it's somehow overbright-ed 4) For drawing to the mask texture i used an extra frame buffer object (FBO) I'm not really happy with the resulting image (overbright-ed picture) nor with the speed achieved with this method. I think the normal way was to draw directly to the grayscale (overlay) texture2D affecting only it's alpha channel in the places where the brush hits. Is there a fast way to achieve this? I have searched a lot and never got an answer that's clear and understandable. Then, in the main draw loop I could only draw the colored texture and then blend the grayscale ontop with glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA). I just want to learn to use OPENGL ES and it's driving me nuts because i can't get it to work properly. An advice, a link to a tutorial would be much appreciated.

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• How do I create a hyperlink in java?

  - by Justin984

  I'm going through the google app engine tutorials at https://developers.google.com/appengine/docs/java/gettingstarted/usingusers I'm very new to google app engine, java and web programming in general. So my question is, at the bottom of the page it says to add a link to allow the user to log out. So far I've got this: public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException { UserService userService = UserServiceFactory.getUserService(); User user = userService.getCurrentUser(); if(user != null){ resp.setContentType("text/plain"); resp.getWriter().println("Hello, " + user.getNickname()); String logoutLink = String.format("<a href=\"%s\">Click here to log out.</a>", userService.createLogoutURL(req.getRequestURI())); resp.getWriter().println(logoutLink); }else { resp.sendRedirect(userService.createLoginURL(req.getRequestURI())); } } However instead of a link, the full string is printed to the screen including the tags. When I look at the page source, I have no tags or any of the other stuff that goes with a webpage. I guess that makes sense considering I've done nothing to output any of that. Do I just do a bunch of resp.GetWriter().println() statements to output the rest of the webpage, or is there something else I don't know about? Thanks!

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• PHP URL parameters append return special character

  - by Alexandre Lavoie

  I'm programming a function to build an URL, here it is : public static function requestContent($p_lParameters) { $sParameters = "?key=TEST&format=json&jsoncallback=none"; foreach($p_lParameters as $sParameterName => $sParameterValue) { $sParameters .= "&$sParameterName=$sParameterValue"; } echo "<span style='font-size: 16px;'>URL : http://api.oodle.com/api/v2/listings" . $sParameters . "</span><br />"; $aXMLData = file_get_contents("http://api.oodle.com/api/v2/listings" . $sParameters); return json_decode($aXMLData,true); } And I am calling this function with this array list : print_r() result : Array ( [region] => canada [category] => housing/sale/home ) But this is very strange I get an unexpected character (note the special character none*®*ion) : http://api.oodle.com/api/v2/listings?key=TEST&format=json&jsoncallback=none®ion=canada&category=housing/sale/home For information I use this header : <meta http-equiv="Content-Type" content="text/html;charset=UTF-8" /> <?php header('Content-Type: text/html;charset=UTF-8'); ?> EDIT : $sRequest = "http://api.oodle.com/api/v2/listings?key=TEST&format=json&jsoncallback=none&region=canada&category=housing/sale/home"; echo "<span style='font-size: 16px;'>URL : " . $sRequest . "</span><br />"; return the exact URL with problem : http://api.oodle.com/api/v2/listings?key=TEST&format=json&jsoncallback=none®ion=canada&category=housing/sale/home Thank you for your help!

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• Populate a tree from Hierarchical data using 1 LINQ statement

  - by Midhat

  Hi. I have set up this programming exercise. using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace ConsoleApplication2 { class DataObject { public int ID { get; set; } public int ParentID { get; set; } public string Data { get; set; } public DataObject(int id, int pid, string data) { this.ID = id; this.ParentID = pid; this.Data = data; } } class TreeNode { public DataObject Data {get;set;} public List<DataObject> Children { get; set; } } class Program { static void Main(string[] args) { List<DataObject> data = new List<DataObject>(); data.Add(new DataObject(1, 0, "Item 1")); data.Add(new DataObject(2, 0, "Item 2")); data.Add(new DataObject(21, 2, "Item 2.1")); data.Add(new DataObject(22, 2, "Item 2.2")); data.Add(new DataObject(221, 22, "Item 2.2.1")); data.Add(new DataObject(3, 0, "Item 3")); } } } The desired output is a List of 3 treenodes, having items 1, 2 and 3. Item 2 will have a list of 2 dataobjects as its children member and so on. I have been trying to populate this tree (or rather a forest) using just 1 SLOC using LINQ. A simple group by gives me the desired data but the challenge is to organize it in TreeNode objects. Can someone give a hint or an impossibility result for this?

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• How would I code a complex formula parser manually?

  - by StormianRootSolver

  Hm, this is language - agnostic, I would prefer doing it in C# or F#, but I'm more interested this time in the question "how would that work anyway". What I want to accomplish ist: a) I want to LEARN it - it's about my ego this time, it's for a fun project where I want to show myself that I'm a really good at this stuff b) I know a tiny little bit about EBNF (although I don't know yet, how operator precedence works in EBNF - Irony.NET does it right, I checked the examples, but this is a bit ominous to me) c) My parser should be able to take this: 5 * (3 + (2 - 9 * (5 / 7)) + 9) for example and give me the right results d) To be quite frankly, this seems to be the biggest problem in writing a compiler or even an interpreter for me. I would have no problem generating even 64 bit assembler code (I CAN write assembler manually), but the formula parser... e) Another thought: even simple computers (like my old Sharp 1246S with only about 2kB of RAM) can do that... it can't be THAT hard, right? And even very, very old programming languages have formula evaluation... BASIC is from 1964 and they already could calculate the kind of formula I presented as an example f) A few ideas, a few inspirations would be really enough - I just have no clue how to do operator precedence and the parentheses - I DO, however, know that it involves an AST and that many people use a stack So, what do you think?

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• Keyboard shortcut to Un/Comment out code in Mathematica 7?

  - by dbjohn

  A keyboard shortcut to comment/uncomment out a piece of code is common in other programming IDE's for languages like Java, .Net. I find it a very useful technique when experimenting through trial and error to temporarily comment out and uncomment lines, words and parts of the code to find out what is and isn't working. I cannot find any such keyboard shortcut on the Mathematica front end in version 7. I know that it is possible to comment out code by selecting the code, right mouse click and select Un/Comment from the menu that appears but this is too slow while coding. I tried to access this using the menu key Menu on the keyboard but Mathematica frontend doesn't respond to or recognise this key unlike other applications, this could have allowed a key combination for commenting. Can someone else verify that this isn't unique to my machine and that the key isn't recognised by mathematica. I looked at this question and looked in the KeyEventTranslations.tr file but I don't think there is any way to create a shortcut to do this(?). Should I just live with it? Any other suggestions? (I have seen there is an Emacs version of mathematica, I have never tried Emacs or this Mma version and imagine that it would have this ability but would prefer not to go to the trouble and uncertainty of installing it. Also I would guess that the Wolfram Workbench could do this, but that may not be worth the investment just for this.)

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• UITableView: NSMutableArray not appearing in table

  - by Michael Orcutt

  I'm new to objective c and iPhone programming. I can't seem to figure out why no cells will fill when I run this code. The xml content displays in the console log and xcode displays no errors. Can any help? - (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName attributes:(NSDictionary *)attributeDict { if(![elementName compare:@"Goal"] ) { tempElement = [[xmlGoal alloc] init]; } else if(![elementName compare:@"Title"]) { currentAttribute = [NSMutableString string]; } else if(![elementName compare:@"Progress"]) { currentAttribute = [NSMutableString string]; } } - (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName { if(![elementName compare:@"Goal"]) { [xmlElementObjects addObject:tempElement]; } else if(![elementName compare:@"Title"]) { NSLog(@"The Title of this event is %@", currentAttribute); [tempElement setTitled:currentAttribute]; } else if(![elementName compare:@"Progress"]) { NSLog(@"The Progress of this event is %@", currentAttribute); [tempElement setProgressed:currentAttribute]; } } - (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string { if(self.currentAttribute) { [self.currentAttribute appendString:string]; } } - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { return [xmlElementObjects count]; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; UITableViewCell *cell = [mtableview dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithFrame:CGRectZero reuseIdentifier:CellIdentifier] autorelease]; } // Set up the cell... cell.textLabel.text = [xmlElementObjects objectAtIndex:indexPath.row]; return cell; } - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { }

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• eclipse - starting with android sdk

  - by dontHaveName

  I want start programming for android.. What I have: -Windows 7 -Eclipse Classic 4.2 -Downloaded all there required files - http://developer.android.com/sdk/installing/adding-packages.html -ADT Plugin I want install new ADT plugin.. at first I tried to download it from http://dl-ssl.google.com/android/eclipse, I add it, but if i selected it there is only "pending.." and nothing has load..(maybe internet connection?I have selected Native connection in preferences after pending it wrotes: Unable to connect to repository http://dl-ssl.google.com/android/eclipse/content.xml org.eclipse.equinox.p2.core.ProvidesException ) Thats why I download ADT plugin. So if I select downloaded ADT plugin - content of it load - developer tools and ndk plugin so I select all and click next. It loads and writes this: "Cannot complete the install because one or more required items could not be found. Software being installed: Android Development Tools 20.0.3.v201208082019-427395 (com.android.ide.eclipse.adt.feature.group 20.0.3.v201208082019-427395) Missing requirement: Android Development Tools 20.0.3.v201208082019-427395 (com.android.ide.eclipse.adt.feature.group 20.0.3.v201208082019-427395) requires 'org.eclipse.wst.sse.core 0.0.0' but it could not be found" requires 'org.eclipse.wst.sse.core 0.0.0 this problem is shown here: http://developer.android.com/resources/faq/troubleshooting.html#installeclipsecomponents but there is solution only for version 3.3 and 3.4 (I have 4.2) anyway but I tried it- I look for updates but nothing were found I really dont know where could be problem.. Thanks for any answer. (sorry for my english) I will send 1€ to somebody who can solve my problem ;) (I think all problems all for internet connection but I cant set it..)

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• Algorithm Question

  - by Ravi

  Hi, I am trying to find a O (n) algorithm for this problem but unable to do so even after spending 3 - 4 hours. The brute force method times out (O (n^2)). I am confused as to how to do it ? Does the solution requires dynamic programming solution ? http://acm.timus.ru/problem.aspx?space=1&num=1794 In short the problem is this: There are some students sitting in circle and each one of them has its own choice as to when he wants to be asked a question from a teacher. The teacher will ask the questions in clockwise order only. For example: 5 3 3 1 5 5 This means that there are 5 students and : 1st student wants to go third 2nd student wants to go third 3rd student wants to go first 4th student wants to go fifth 5th student wants to go fifth. The question is as to where should teacher start asking questions so that maximum number of students will get the turn as they want. For this particular example, the answer is 5 because 3 3 1 5 5 2 3 4 5 1 You can see that by starting at fifth student as 1st, 2 students (3 and 5) are getting the choices as they wanted. For this example the answer is 12th student : 12 5 1 2 3 6 3 8 4 10 3 12 7 because 5 1 2 3 6 3 8 4 10 3 12 7 2 3 4 5 6 7 8 9 10 11 12 1 four students get their choices fulfilled. Thanks Ravi

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• A Newbie question regarding Software Development

  - by Sharif

  Hi, I'm going to complete my B.pharm (Hons.) degree and, you know, I don't have much knowledge about programing. I was wondering to build a software on my own. Could you guys tell me what to learn first for that? Is it too hard for a student of other discipline to build a software? Let me know please. The software I want to make is like a dictionary (or more specifically like "Physician's Desk Reference"). It should find the generic name, company name, indication, price etc. of a drug when I enter the brand name and vice versa. To build a software like that what programing language could help me most and what (and how many) language should I learn first? In my country, there is no practice of Community pharmacy (most of the pharmacy stores are run by unskilled people), that's why this type of thing could help them sell drugs. Would you please tell me what I'm to do and how tough it is? I'm very keen to learn programming. Thanks in advance NB: I started this post in ASKREDDIT section but it seems that was not the right place for poll type question, so I post it again in this section

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• need help with Java solution /newbie

  - by Racket

  Hi, I'm new to programming in general so i'm trying to be as specific as possible in this question. There's this book that i'm doing some exercises on. I managed to do more than half of what they say, but it's just one input that I have been struggling to find out. I'll write the question and thereafter my code, "Write an application that creates and prints a random phone number of the form XXX-XXX-XXXX. Include the dashes in the output. Do not let the first three digits contain an 8 or 9 (but don't be more restrictive than that), and make sure that the second set of three digits is not greater than 742. Hint: Think through the easiest way to construct the phone number. Each diigit does not have to be determined separately." OK, the highlighted sentence is what i'm looking at. Here's my code: import java.util.Random; public class PP33 { public static void main (String[] args) { Random rand = new Random(); int num1, num2, num3; num1 = rand.nextInt(900) + 100; num2 = rand.nextInt(643) + 100; num3 = rand.nextInt(9000) + 1000; System.out.println(num1+"-"+num2+"-"+num3); } } How am I suppose to do this? I'm on chapter 3 so we have not yet discussed if statements etcetera, but Aliases, String class, Packages, Import declaration, Random Class, Math Class, Formatting output (decimal- & numberFormat), Printf, Enumeration & Wrapper classes + autoboxing. So consider answer the question based only on these assumptions, please. The code doesn't have any errors. Thank you!

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• How would you implement a hashtable in language x?

  - by mk

  The point of this question is to collect a list of examples of hashtable implementations using arrays in different languages. It would also be nice if someone could throw in a pretty detailed overview of how they work, and what is happening with each example. Edit: Why not just use the built in hash functions in your specific language? Because we should know how hash tables work and be able to implement them. This may not seem like a super important topic, but knowing how one of the most used data structures works seems pretty important to me. If this is to become the wikipedia of programming, then these are some of the types of questions that I will come here for. I'm not looking for a CS book to be written here. I could go pull Intro to Algorithms off the shelf and read up on the chapter on hash tables and get that type of info. More specifically what I am looking for are code examples. Not only for me in particular, but also for others who would maybe one day be searching for similar info and stumble across this page. To be more specific: If you had to implement them, and could not use built-in functions, how would you do it? You don't need to put the code here. Put it in pastebin and just link it.

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• Socket isn't listed by netstat unless using certain ports

  - by illuzive

  I'm a computer science student with a few years of programming experience. Yesterday, while working on a project (Mac OS X, BSD sockets) at school, I encountered a strange problem. I was adding several modules to a very basic "server" (mostly a bunch of functions to set up and manage an UDP socket on a certain port). While doing this, I started the server from time to time in order to see that everything worked like it should. I've been using port 32000 during the development of the server. When I start the server and run netstat, the socket is listed as expected. > netstat -p UDP | grep 32000 udp46 0 0 *.32000 *.* However, when I run the server on other ports (random (10000 - 50000)), it's not listed by netstat. My thought was that I had somehow hard coded the port somewhere in the code, but that's not the case. The thing is - I can connect to the socket on any of the tested ports, and it reads data sent to it without any problem at all. It just doesn't get listed by netstat. What I wonder, is if anyone of you have any idea of why this happens? Note: Although this is a project at school, it's not homework. This is just something I want to understand for my own benefit.

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• Silverlight, Flash, or JavaScript for web app that runs client-side, or just stick with C#?

  - by Sootah

  Silverlight, Flash, and JavaScript, oh my.. I have a couple of applications that I need to develop for one of my business partners that will be distributed to dozens of people. These applications will need to be able to query information from the internet (query via Google, grab feeds from our other sites, just general web access) and save files to their computer. The reason I want to host the application is so that it all can be centrally managed, and any updates would be instantly deployed to everyone that uses the service. There always seems to be headaches with developing a pure desktop app in a language like C# with regards to making sure people use the latest version, don't have some odd problem with the installer, etc. Since we don't want to tie up our server's CPU I want effectively all of the processing done client-side. Meaning that they would log into their account, access the app, and then all the work done within the app is all handled by their machine. Only specific data would be sent back to the server. So - which language is best for this? Microsoft's Silverlight, Adobe's Flash, or Sun's JavaScript? I've heard a lot of good things about Silverlight and have wanted to try it for some time. I've only done extremely limited JavaScript programming, and absolutely none with Flash. Or, with my main requirement being that the client does all of its own processing should I just stick with C#? Also, is there any way to integrate a C# app into a webpage? I've never even considered it (or have any idea if it's even possible) until just now. Thanks in advance! -Sootah

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• Strange problem with simple multithreading program in Java

  - by Elizabeth

  Hello, I am just starting play with multithreading programming. I would like to my program show alternately character '-' and '+' but it doesn't. My task is to use synchronized keyword. As far I have: class FunnyStringGenerator{ private char c; public FunnyStringGenerator(){ c = '-'; } public synchronized char next(){ if(c == '-'){ c = '+'; } else{ c = '-'; } return c; } } class ThreadToGenerateStr implements Runnable{ FunnyStringGenerator gen; public ThreadToGenerateStr(FunnyStringGenerator fsg){ gen = fsg; } @Override public void run() { for(int i = 0; i < 10; i++){ System.out.print(gen.next()); } } } public class Main{ public static void main(String[] args) throws IOException { FunnyStringGenerator FSG = new FunnyStringGenerator(); ExecutorService exec = Executors.newCachedThreadPool(); for(int i = 0; i < 20; i++){ exec.execute(new ThreadToGenerateStr(FSG)); } } } EDIT: I also testing Thread.sleep in run method instead for loop.

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• Rails - any fancy ways to handle 404s?

  - by jyoseph

  I have a rails app I built for an old site I converted from another cms (in a non-rails language, hehe). Most of the old pages are mapped to the new pages using routes.rb. But there are still a few 404s. I am a rails newb so I'm asking if there are any advanced ways to handle 404s. For example, if I was programming in my old language I'd do this: Get the URL (script_name) that was being accessed and parse it. Do a lookup in the database for any keywords, ids, etc found in the new URL. If found, redirect to the page (or if multiple records are found, show them all on a results page and let user choose). With rails I'd probably want to do :status = :moved_permanently I'm guessing? If not found, show a 404. Are there any gems/plugins or tutorials you know of that would handle such a thing, if it's even possible. Or can you explain on a high level how that can be done? I don't need a full code sample, just a push in the right direction. PS. It's a simple rails 3 app that uses a single Content model.

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• How to handle 'this' pointer in constructor?

  - by Kyle

  I have objects which create other child objects within their constructors, passing 'this' so the child can save a pointer back to its parent. I use boost::shared_ptr extensively in my programming as a safer alternative to std::auto_ptr or raw pointers. So the child would have code such as shared_ptr<Parent>, and boost provides the shared_from_this() method which the parent can give to the child. My problem is that shared_from_this() cannot be used in a constructor, which isn't really a crime because 'this' should not be used in a constructor anyways unless you know what you're doing and don't mind the limitations. Google's C++ Style Guide states that constructors should merely set member variables to their initial values. Any complex initialization should go in an explicit Init() method. This solves the 'this-in-constructor' problem as well as a few others as well. What bothers me is that people using your code now must remember to call Init() every time they construct one of your objects. The only way I can think of to enforce this is by having an assertion that Init() has already been called at the top of every member function, but this is tedious to write and cumbersome to execute. Are there any idioms out there that solve this problem at any step along the way?

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• How do I create a simple Windows form to access a SQL Server database?

  - by NoCatharsis

  I believe this is a very novice question, and if I'm using the wrong forum to ask, please advise. I have a basic understanding of databasing with MS SQL Server, and programming with C++ and C#. I'm trying to teach myself more by setting up my own database with MS SQL Server Express 2008 R2 and accessing it via Windows forms created in C# Express 2010. At this point, I just want to keep it to free or Express dev tools (not necessarily Microsoft though). Anyway, I created a database using the instructions provided here and I set the data types appropriately for each column (no errors in setup at least). Now I'm designing the GUI in C# Express but I've kind of hit a wall as far as the database connection. Is there a simple way to access the database I created locally using C# Express? Can anyone suggest a guide that has all this spelled out already? I am a self-learner so I look forward to teaching myself how to use these applications, but any pointers to start me off in the right direction would be greatly appreciated.

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• How do I add code automatically to a derived function in C++

  - by Ian

  I have code that's meant to manage operations on both a networked client and a server, since there is significant overlap between the two. However, there are a few functions here and there that are meant to be exclusively called by the client or server, and accidentally calling a client function on the server (or vice versa) is a significant source of bugs. To reduce these sorts of programming errors, I'm trying to tag functions so that they'll raise a ruckus if they're misused. My current solution is a simple macro at the start of each function that calls an assert if the client or server accesses members they shouldn't. However, this runs into problems when there are multiple derived instances of classes, in that I have to tag the implementation as client or server side in EVERY child class. What I'd like to be able to do is put a tag in the virtual member's signature in the base class, so that I only have to tag it once and not run into errors by forgetting to do it repeatedly. I've considered putting a check in a base class implementation and then referring to it with something like base::functionName, but that runs into the same issue as far as needing to manually add the function call to every implementation. Ideally, I'd be able to have parent versions of the function called automatically like default constructors do. Does anybody know how to achieve something like this in C++? Is there an alternate approach I should be considering? Thanks!

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• When to drop an IT job

  - by Nippysaurus

  In my career I have had two programming jobs. Both these jobs were in a field that I am most familiar with (C# / MSSQL) but I have quit both jobs for the same reason: unmanageable code and bad (loose) company structure. There was something in common with both these jobs: small companies (in one I was the only developer). Currently I am in the following position: being given written instructions which are almost impossible to follow (somewhat of a fools errand). we are given short time constraints, but seldom asked how long work will take, and when we do it is always too long and needs to be shorter (and when it ends up taking longer than they need it to take, it's always our fault). there is no time for proper documenting, but we get blamed for not documenting (see previous point). Management is constantly screwing me around, saying I'm underperforming on a given task (which is not true, and switching me to a task which is much more confusing). So I must ask my fellow developers: how bad does a job need to be before you would consider jumping ship? And what to look out for when considering taking a job. In future I will be asking about documented procedures, release control, bug management and adoption of new technologies. EDIT: Let me add some more fuel to the fire ... I have been in my current job for just over a year, and the work I am doing almost never uses any of the knowledge I have gained from the other work I have been doing here. Everything is a giant learning curve. Because of this about 30% of my time is learning what is going on with this new product (who's owner / original developer has left the company), 30% trying to find the relevant documentation that helps the whole thing make sense, 30% actually finding where to make the change, 10% actually making the change.

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• Using shared_ptr to implement RCU (read-copy-update)?

  - by yongsun

  I'm very interested in the user-space RCU (read-copy-update), and trying to simulate one via tr1::shared_ptr, here is the code, while I'm really a newbie in concurrent programming, would some experts help me to review? The basic idea is, reader calls get_reading_copy() to gain the pointer of current protected data (let's say it's generation one, or G1). writer calls get_updating_copy() to gain a copy of the G1 (let's say it's G2), and only one writer is allowed to enter the critical section. After the updating is done, writer calls update() to do a swap, and make the m_data_ptr pointing to data G2. The ongoing readers and the writer now hold the shared_ptr of G1, and either a reader or a writer will eventually deallocate the G1 data. Any new readers would get the pointer to G2, and a new writer would get the copy of G2 (let's say G3). It's possible the G1 is not released yet, so multiple generations of data my co-exists. template <typename T> class rcu_protected { public: typedef T type; typedef std::tr1::shared_ptr<type> rcu_pointer; rcu_protected() : m_data_ptr (new type()) {} rcu_pointer get_reading_copy () { spin_until_eq (m_is_swapping, 0); return m_data_ptr; } rcu_pointer get_updating_copy () { spin_until_eq (m_is_swapping, 0); while (!CAS (m_is_writing, 0, 1)) {/* do sleep for back-off when exceeding maximum retry times */} rcu_pointer new_data_ptr(new type(*m_data_ptr)); // as spin_until_eq does not have memory barrier protection, // we need to place a read barrier to protect the loading of // new_data_ptr not to be re-ordered before its construction _ReadBarrier(); return new_data_ptr; } void update (rcu_pointer new_data_ptr) { while (!CAS (m_is_swapping, 0, 1)) {} m_data_ptr.swap (new_data_ptr); // as spin_until_eq does not have memory barrier protection, // we need to place a write barrier to protect the assignments of // m_is_writing/m_is_swapping be re-ordered bofore the swapping _WriteBarrier(); m_is_writing = 0; m_is_swapping = 0; } private: volatile long m_is_writing; volatile long m_is_swapping; rcu_pointer m_data_ptr; };

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