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• Should I close sockets from both ends?

  - by Roman

  I have the following problem. My client program monitor for availability of server in the local network (using Bonjour, but it does not rally mater). As soon as a server is "noticed" by the client application, the client tries to create a socket: Socket(serverIP,serverPort);. At some point the client can loose the server (Bonjour says that server is not visible in the network anymore). So, the client decide to close the socket, because it is not valid anymore. At some moment the server appears again. So, the client tries to create a new socket associated with this server. But! The server can refuse to create this socket since it (server) has already a socket associated with the client IP and client port. It happens because the socket was closed by the client, not by the server. Can it happen? And if it is the case, how this problem can be solved? Well, I understand that it is unlikely that the client will try to connect to the server from the same port (client port), since client selects its ports randomly. But it still can happen (just by chance). Right?

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• Project euler problem 3 in haskell

  - by shk

  I'm new in Haskell and try to solve 3 problem from http://projecteuler.net/. The prime factors of 13195 are 5, 7, 13 and 29. What is the largest prime factor of the number 600851475143 ? My solution: import Data.List getD :: Int -> Int getD x = -- find deviders let deriveList = filter (\y -> (x `mod` y) == 0) [1 .. x] filteredList = filter isSimpleNumber deriveList in maximum filteredList -- Check is nmber simple isSimpleNumber :: Int -> Bool isSimpleNumber x = let deriveList = map (\y -> (x `mod` y)) [1 .. x] filterLength = length ( filter (\z -> z == 0) deriveList) in case filterLength of 2 -> True _ -> False I try to run for example: getD 13195 > 29 But when i try: getD 600851475143 I get error Exception: Prelude.maximum: empty list Why? Thank you @Barry Brown, I think i must use: getD :: Integer -> Integer But i get error: Couldn't match expected type `Int' with actual type `Integer' Expected type: [Int] Actual type: [Integer] In the second argument of `filter', namely `deriveList' In the expression: filter isSimpleNumber deriveList Thank you.

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• Retrieve class name hierarchy as string

  - by Jeff Wain

  Our system complexity has risen to the point that we need to make permission names tied to the client from the database more specific. In the client, permissions are referenced from a static class since a lot of client functionality is dependent on the permissions each user has and the roles have a ton of variety. I've referenced this post as an example, but I'm looking for a more specific use case. Take for instance this reference, where PermissionAlpha would be a const string: return HasPermission(PermissionNames.PermissionAlpha); Which is great, except now that things are growing more complex the classes are being structured like this: public static class PermissionNames { public static class PermissionAlpha { public const string SubPermission; } } I'm trying to find an easy way to reference PermissionAlpha in this new setup that will act similar to the first declaration above. Would the only way to do this be to resort to pulling the value of the class name like in the example below? I'm trying to keep all the names in one place that can be reference anywhere in the application. public static class PermissionAlpha { public static string Name { get { return typeof(PermissionAlpha).Name; } } }

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• How to calculate the normal of points on a 3D cubic Bézier curve given normals for its start and end points?

  - by Robert

  I'm trying to render a "3D ribbon" using a single 3D cubic Bézier curve to describe it (the width of the ribbon is some constant). The first and last control points have a normal vector associated with them (which are always perpendicular to the tangents at those points, and describe the surface normal of the ribbon at those points), and I'm trying to smoothly interpolate the normal vector over the course of the curve. For example, given a curve which forms the letter 'C', with the first and last control points both having surface normals pointing upwards, the ribbon should start flat, parallel to the ground, slowly turn, and then end flat again, facing the same way as the first control point. To do this "smoothly", it would have to face outwards half-way through the curve. At the moment (for this case), I've only been able to get all the surfaces facing upwards (and not outwards in the middle), which creates an ugly transition in the middle. It's quite hard to explain, I've attached some images below of this example with what it currently looks like (all surfaces facing upwards, sharp flip in the middle) and what it should look like (smooth transition, surfaces slowly rotate round). Silver faces represent the front, black faces the back. Incorrect, what it currently looks like: Correct, what it should look like: All I really need is to be able to calculate this "hybrid normal vector" for any point on the 3D cubic bézier curve, and I can generate the polygons no problem, but I can't work out how to get them to smoothly rotate round as depicted. Completely stuck as to how to proceed!

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• What is the best Design/Way to keep user connected ?

  - by Fasih Hansmukh

  Am working on a POC for self learning in which I want to keep my user connected in LIVE pattern. For example, A game in which 4 user can play at a time , here I need to keep this user connected to my game . M not good at Socket type of programming and love to do that in Services way.What i wana know is 'What is the best way of doing this'. According to my initial Brain Storming, I have decided that I will use SilverLight(In Browser Or Out of Browser) as Front end [I have no issue in that]. I m more concern in back end. Either I make an handler or make a WCF service or use full duplex service and use pooling mechanism for that. As a random thought I come up with a Timer type logic that will fire every after 10 seconds at clients end and get status like Is it now Its turn to roll a dice Home many user left (in case if some of them left) What are connected user status in game like there score/points ect and update game view according to this at his end Kindly place your best answers here that will help me to learn this. Regards and thanks in Advance EDIT: Starting Bounty as i need more feedback. FH

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• Linq2Sql: query - subquery optimisation

  - by Budda

  I have the following query: IList<InfrStadium> stadiums = (from sector in DbContext.sectors where sector.Type=typeValue select new InfrStadium(sector.TeamId) ).ToList(); and InfrStadium class constructor: private InfrStadium(int teamId) { IList<Sector> teamSectors = (from sector in DbContext.sectors where sector.TeamId==teamId select sector) .ToList<>(); ... work with data } Current implementation perform 1+n queries, where n - number of records fetched the 1st time. I want to optimize that. And another one I would love to do using 'group' operator in way like this: IList<InfrStadium> stadiums = (from sector in DbContext.sectors group sector by sector.TeamId into team_sectors select new InfrStadium(team_sectors.Key, team_sectors) ).ToList(); with appropriate constructor: private InfrStadium(int iTeamId, IEnumerable<InfrStadiumSector> eSectors) { IList<Sector> teamSectors = eSectors.ToList(); ... work with data } But attempt to launch query causes the following error: Expression of type 'System.Int32' cannot be used for constructor parameter of type 'System.Collections.Generic.IEnumerable`1[InfrStadiumSector]' Question 1: Could you please explain, what is wrong here, I don't understand why 'team_sectors' is applied as 'System.Int32'? I've tried to change query a little (replace IEnumerable with IQueryeable): IList<InfrStadium> stadiums = (from sector in DbContext.sectors group sector by sector.TeamId into team_sectors select new InfrStadium(team_sectors.Key, team_sectors.AsQueryable()) ).ToList(); with appropriate constructor: private InfrStadium(int iTeamId, IQueryeable<InfrStadiumSector> eSectors) { IList<Sector> teamSectors = eSectors.ToList(); ... work with data } In this case I've received another but similar error: Expression of type 'System.Int32' cannot be used for parameter of type 'System.Collections.Generic.IEnumerable1[InfrStadiumSector]' of method 'System.Linq.IQueryable1[InfrStadiumSector] AsQueryableInfrStadiumSector' Question 2: Actually, the same question: can't understand at all what is going on here... P.S. I have another to optimize query idea (describe here: Linq2Sql: query optimisation) but I would love to find a solution with 1 request to DB).

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• LDAP/AD Integrated Group/Membership Management Package suitable for embedding in an application

  - by Ernest

  In several web applications, it is often necessary to define groups of users for purposes of membership as well as role management. For example, in one of our applications we would like to user a group of "Network Engineers" and another group that consists of "Managers" of such Network Engineers. The information we need is contact details of members of each group. So far, we have written our own tools to allow the administrator of the application to add/delete/move groups and their memberships and either store them in a XML file or a database. Increasingly, companies already have the groups we want defined in LDAP/AD, so it would be best to create a pointer in our application to the correspoding group in LDAP. Although there are a number of LDAP libraries and LDAP browsers available and we could code this and provide a web front end to get a list of available groups and their members, we are wondering if there is already a "component framework" available that would readily provide this LDAP browsing functionality that we could just embed this into our application. Something between a library and a full LDAP browser product ? (To clarify, the use case is for an admin of our web application to create a locally relevant group name and then map it to an exiting LDAP group. To enable this in the UI, we would like to present a way for the admin to browse available groups in the company LDAP server, view their membership, and select the LDAP group they would like to map to the locally relevant group name. In a second step, we would then synchronize the members of that LDAP group and their contact details to a store in our application ) Appreciate any pointers.

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• Multi-Precision Arithmetic on MIPS

  - by Rob

  Hi, I am just trying to implement multi-precision arithmetic on native MIPS. Assume that one 64-bit integer is in register $12 and $13 and another is in registers $14 and $15. The sum is to be placed in registers $10 and $11. The most significant word of the 64-bit integer is found in the even-numbered registers, and the least significant word is found in the odd-numbered registers. On the internet, it said, this is the shortest possible implementation. addu $11, $13, $15 # add least significant word sltu $10, $11, $15 # set carry-in bit addu $10, $10, $12 # add in first most significant word addu $10, $10, $14 # add in second most significant word I just wanna double check that I understand correctly. The sltu checks if the sum of the two least significant words is smaller or equal than one of the operands. If this is the case, than did a carry occur, is this right? To check if there occured a carry when adding the two most significant words and store the result in $9 I have to do: sltu $9, $10, $12 # set carry-in bit Does this make any sense?

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• PHP, MySQL prepared statements - can you use results of execute more than once by calling data_seek(

  - by Carvell Fenton

  Hello, I have a case where I want to use the results of a prepared statement more than once in a nested loop. The outer loop processes the results of another query, and the inner loop is the results of the prepared statement query. So the code would be something like this (just "pseudoish" to demonstrate the concept): // not showing the outer query, it is just a basic SELECT, not prepared statement // we'll call it $outer_query $obj_array = array(); // going to save objects in this $ids = array(18,19,20); // just example id numbers $query = "SELECT field1, field2 FROM table1 WHERE id=?"; $stmt = $db->prepare($query); foreach ($ids as $id) { $stmt->bind_param("i", $id); $stmt->execute(); $stmt->bind_result($var1, $var2); $stmt->store_result(); // I think I need this for data_seek while ($q1 = $outer_query->fetch_object()) { while ($stmt->fetch()) { if ($q1->field1 == $var1) { // looking for a match $obj = new stdClass(); $obj->var1 = $var1; $obj->var2 = $var2; $obj_array[] = $obj; $stmt->data_seek(0); // reset for outer loop break; // found match, so leave inner } } } } The problem I seem to be experiencing is that the values are not getting bound in the variables as I would expect after the first time I use fetch in the inner loop. Specifically, in one example I ran with 3 ids for the foreach, the first id was processed correctly, the second was processed incorrectly (matches were not found in the inner loop even though they existed), and then the third was processed correctly. Is there something wrong with the prepared statment function calls in the sequence I am doing above, or is this an invalid way to use the results of the prepared statement? Thanks.

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• Objective-C properties are not being recognized in header file?

  - by Greg

  Hey folks, I wonder if I'm doing something completely stupid here... I'm clearly missing something. I've gotten used to the pattern of defining properties of a custom class, however I seem to be hitting a point where extended classes do not recognize new properties. Case of point, here's my header file: import import "MyTableViewController.h" @interface MyRootController : MyTableViewController { NSMutableArray *sectionList; } @property (nonatomic, retain) NSMutableArray *sectionList; @end Now, for some reason that "sectionList" property is not turning green within my interface file (ie: it's not being recognized as custom property it seems). As a result, I'm getting all kinds of errors down in my implementation. The first is right at the top of my implementation where I try to synthesize the property: import "MyRootController.h" @implementation MyRootController @synthesize sectionList; That synthesize line throws the error "No declaration of property 'sectionList' found in the interface". So, this is really confusing. I'm clearly doing something wrong, although I can't put my finger on what. One thought: I am extending another custom class of my own. Do I need to specify some kind of super-class declaration to keep the architecture from getting sealed one level up? Thanks!

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• TransactionRequiredException on OptimisticLockException

  - by João Madureira Pires

  Hi there. I have the following class that generates sequencial Card Numbers. I'm trying to recover from OptimisticLockException, by calling recursively the same method. however, i'm getting TransactionRequiredException. Dows anyone knows how to recover from OptimisticLockException in my case? Thanks a lot in advance @Name("simpleAutoIncrementGenerator") public class SimpleAutoIncrementGenerator extends CardNumberGenerator{ private static final long serialVersionUID = 2869548248468809665L; private int numberOfRetries = 0; @Override public String generateNextNumber(CardInstance cardInstance, EntityManager entityManager) { try{ EntityCard card = (EntityCard)entityManager.find(EntityCard.class, cardInstance.getId()); if(card != null){ String nextNumber = ""; String currentNumber = card.getCurrentCardNumber(); if(currentNumber != null && !currentNumber.isEmpty()){ Long numberToInc = Long.parseLong(currentNumber); numberToInc ++; nextNumber = String.valueOf(numberToInc); card.setCurrentCardNumber(nextNumber); // this is just to cause a OptimisticLock Exception try { Thread.sleep(4000); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } entityManager.persist(card); entityManager.flush(); return nextNumber; } } }catch (OptimisticLockException oLE) { System.out.println("\n\n\n\n OptimisticLockException \n\n\n\n"); if(numberOfRetries < CentralizedConfig.CARD_NUMBER_GENERATOR_MAX_TRIES){ numberOfRetries ++; return generateNextNumber(cardInstance,entityManager); } }catch (TransactionRequiredException trE) { System.out.println("\n\n\n\n TransactionRequiredException \n\n\n\n"); if(numberOfRetries < CentralizedConfig.CARD_NUMBER_GENERATOR_MAX_TRIES){ numberOfRetries ++; return generateNextNumber(cardInstance,entityManager); } }catch (StaleObjectStateException e) { System.out.println("\n\n\n\n StaleObjectStateException \n\n\n\n"); if(numberOfRetries < CentralizedConfig.CARD_NUMBER_GENERATOR_MAX_TRIES){ numberOfRetries ++; return generateNextNumber(cardInstance,entityManager); } } return null; } }

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• Real time location tracking - windows program or browser based?

  - by mawg

  I want to track a few hundred, maybe a few thousand people in real time. Let's say that the hardware aspects are sorted out and I can get the data into a database. Now, I want to get it out and show it, in real-time. Weeeell ... "real-enough" time. Let's say that I want to draw a floorplan of a building and plot everyone every 1 to 5 seconds. (I might want to show only certain "kinds" of people at the click of a button; I will need datamining, etc, but let's stick with the worse case scenario). I am comfortable enough with PHP, though not this sort of thing. I personally would be happier with a windows app coded in Delphi, but the trend seems to be to make everything browser based. So, the question, I guess is whether a browser can handle this and whether there are compelling arguments for a windows-based or browser-based solution. If browser-based can handle this (displaying a few thousand data-points a second), and there are no overwhelming arguments for windows then I guess I will go for browser-based and learn a few new tricks. The obvious advantage being that I could also re-use a large part of my code for (vehicle) tracking on Google maps.

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• Are game engines developed in the USA?

  - by numerical25

  I just finished talking to a Flashpoint Academy recruiter about their curriculum. I told him that after I graduate, I would like to go more in-depth with learning game engines and how to make games. So I asked him did their school teach anything in regards to learning any graphics API such as DirectX. He asked me to elaborate a little more as if he was not sure what I was talking about. So I asked did their school teach on how to build game engines. He said "no we only teach with the tools at hand, such as XNA, or the Unreal engine". He further said "most jobs that deal with building game engines go overseas and most of creative work is done in the United States." To be honest, I really had no intentions of going to this school. I just wanted to learn more about the school in case I had second thoughts somewhere down the line. To me I thought it was a bunch of BS, but my question is to you guys, "is it" ??

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• Measuring time spent in application / thread

  - by Adamski

  I am writing a simulation in Java whereby objects act under Newtonian physics. An object may have a force applied to it and the resulting velocity causes it to move across the screen. The nature of the simulation means that objects move in discrete steps depending on the time ellapsed between the current and previous iteration of the animation loop; e.g public void animationLoop() { long prev = System.currentTimeMillis(); long now; while(true) { long now = System.currentTimeMillis(); long deltaMillis = now - prev; prev = now; if (deltaMillis > 0) { // Some time has passed for (Mass m : masses) { m.updatePosition(deltaMillis); } // Do all repaints. } } } A problem arises if the animation thread is delayed in some way causing a large amount of time to ellapse (the classic case being under Windows whereby clicking and holding on minimise / maximise prevents a repaint), which causes objects to move at an alarming rate. My question: Is there a way to determine the time spent in the animation thread rather than the wallclock time, or can anyone suggest a workaround to avoid this problem? My only thought so far is to contstrain deltaMillis by some upper bound.

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• How to add an extra plist property using CMake?

  - by Jesse Beder

  I'm trying to add the item <key>UIStatusBarHidden</key><true/> to my plist that's auto-generated by CMake. For certain keys, it appears there are pre-defined ways to add an item; for example: set(MACOSX_BUNDLE_ICON_FILE ${ICON}) But I can't find a way to add an arbitrary property. I tried using the MACOSX_BUNDLE_INFO_PLIST target property as follows: I'd like the resulting plist to be identical to the old one, except with the new property I want, so I just copied the auto-generated plist and set that as my template. But the plist uses some Xcode variables, which also look like ${foo}, and CMake grumbles about this: Syntax error in cmake code when parsing string <string>com.bedaire.${PRODUCT_NAME:identifier}</string> syntax error, unexpected cal_SYMBOL, expecting } (47) Policy CMP0010 is not set: Bad variable reference syntax is an error. Run "cmake --help-policy CMP0010" for policy details. Use the cmake_policy command to set the policy and suppress this warning. This warning is for project developers. Use -Wno-dev to suppress it. In any case, I'm not even sure that this is the right thing to do. I can't find a good example or any good documentation about this. Ideally, I'd just let CMake generate everything as before, and just add a single extra line. What can I do?

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• Is it a good idea to use MySQL and Neo4j together?

  - by Sanoj

  I will make an application with a lot of similar items (millions), and I would like to store them in a MySQL database, because I would like to do a lot of statistics and search on specific values for specific columns. But at the same time, I will store relations between all the items, that are related in many connected binary-tree-like structures (transitive closure), and relation databases are not good at that kind of structures, so I would like to store all relations in Neo4j which have good performance for this kind of data. My plan is to have all data except the relations in the MySQL database and all relations with item_id stored in the Neo4j database. When I want to lookup a tree, I first search the Neo4j for all the item_id:s in the tree, then I search the MySQL-database for all the specified items in a query that would look like: SELECT * FROM items WHERE item_id = 45 OR item_id = 345435 OR item_id = 343 OR item_id = 78 OR item_id = 4522 OR item_id = 676 OR item_id = 443 OR item_id = 4255 OR item_id = 4345 Is this a good idea, or am I very wrong? I haven't used graph-databases before. Are there any better approaches to my problem? How would the MySQL-query perform in this case?

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• PHP sessions dying in a few seconds

  - by beauchette

  I have a problem with my server : my sessions are dying on their own after a few seconds. here are two page examples : page1.php : <? session_start(); $_SESSION['x'] = 'moo'; ?> page2.php : <? session_start(); echo $_SESSION['x']; ?> php's settings are debian's untouched : no auto start, 1440 seconds maxlifetime, etc so, if I visit page1.php et then page2.php I'm supposed to see 'moo' for 24 minutes, in my case, you have 'moo' for about 5 seconds. Then I observed that the actual session file, was 44 bytes long, and then 0 a few seconds later, without any other intervention than a few 'ls' to observe the phenomenon, I really have no clue as to what happens and any help would be appreciated. EDIT: after some fiddling (mainly not doing much besides restarting my server 3 or 4 times) I was able to have my quick example working. and then I noticed that sessions in my session.save_path directory are all 44 bytes except for some that are 0 bytes, so it's like it's working but not always. which is even more frustrating.

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• How to (kindly) ask your users to upgrade from IE6?

  - by nickf

  It's no secret at all that IE6 has been a major roadblock to the advancement of the web over the last few years. I couldn't count the number of hours I've spent bashing my head against a wall trying to fix or debug IE6 issues. The way I see it, there are two types of IE6 user. a) the poor corporate schmoe whose IT department doesn't want to upgrade in case something breaks, and b) the mums and dads of the world who think the internet is the blue E on their desktop (and I don't mean that in a nasty way). There's probably a couple of people who know about all the other browsers, but still choose to run IE6. They get what they deserve, IMO. Anyway, getting to the point, I'd say that 90% of my IE6-using visitors are in the the mums and dads category - they're not stupid, they just don't know WHY they should upgrade to IE7 or Firefox or whatever. How do I educate these people without pissing them off? Is there a nice and friendly website I can direct these people to, which explains the reasons for upgrading in plain language? Any mention of "security" or "web standards" I think would just come across as scary. I've just seen http://www.whatbrowser.org which seems to fit the bill nicely. It explains in very basic terms: what a web browser is why you'd want to upgrade it how old your current browser is (subtle hint to those with a 9 year old browser) ..aaaand it's in 22 languages. It's from Google but displays no bias (it links to Firefox, Chrome, Opera, Safari, Internet Explorer displayed in a random order).

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• SQLAlchemy Custom Type Which Contains Multiple Columns

  - by Kekoa

  I would like to represent a datatype as a single column in my model, but really the data will be stored in multiple columns in the database. I cannot find any good resources on how to do this in SQLAlchemy. I would like my model to look like this(this is a simplified example using geometry instead of my real problem which is harder to explain): class 3DLine(DeclarativeBase): start_point = Column(my.custom.3DPoint) end_point = Column(my.custom.3DPoint) This way I could assign an object with the (x, y, z) components of the point at once without setting them individually. If I had to separate each component, this could get ugly, especially if each class has several of these composite objects. I would combine the values into one encoded field except that I need to query each value separately at times. I was able to find out how to make custom types using a single column in the documentation. But there's no indication that I can map a single type to multiple columns. I suppose I could accomplish this by using a separate table, and each column would be a foreign key, but in my case I don't think it makes sense to have a one to one mapping for each point to a separate table, and this still does not give the ability to set the related values all at once.

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• Truncating a string while storing it in an array in c

  - by Nick

  I am trying to create an array of 20 character strings with a maximum of 17 characters that are obtained from a file named "words.dat". After that the program should truncate the string only showing the first 17 characters and completely ignore the rest of that string. However My question is: I am not quite sure how to accomplish this, can anyone give me some insight on how to accomplish this task? Here is my current code as is: #include <stdio.h> #include <stdlib.h> #define WORDS 20 #define LENGTH 18 char function1(char[WORDS][LENGTH]); int main( void ) { char word_array [WORDS] [LENGTH]; function1(word_array); return ( 0 ) ; } char function1(char word_array[WORDS][LENGTH]) { FILE *wordsfile = fopen("words.dat", "r"); int i = 0; if (wordsfile == NULL) printf("\nwords.dat was not properly opened.\n"); else { for (i = 0; i < WORDS; i++) { fscanf(wordsfile, "%17s", word_array[i]); printf ("%s \n", word_array[i]); } fclose(wordsfile); } return (word_array[WORDS][LENGTH]); } words.dat file: Ninja DragonsFury failninja dragonsrage leagueoflegendssurfgthyjnu white black red green yellow green leagueoflegendssughjkuj dragonsfury Sword sodas tiger snakes Swords Snakes sage Sample output: blahblah@fang:~>a.out Ninja DragonsFury failninja dragonsrage leagueoflegendssu rfgthyjnu white black red green yellow green leagueoflegendssu ghjkuj dragonsfury Sword sodas tiger snakes Swords blahblah@fang:~> What will be accomplished afterwards with this program is: After function1 works properly I will then create a second function name "function2" that will look throughout the array for matching pairs of words that match "EXACTLY" including case . After I will create a third function that displays the 20 character strings from the words.dat file that I previously created and the matching words.

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• Developping an online music store

  - by Simon

  We need to develop an application to sell music online. No need to specify that all will be done quite legally and in so doing, we have to plan an interface to pay artists. However, we are confronted with a question: What is the best way to store music on the server? Should we save it on server's disk from a HTTP fileupload? Should we save via FTP or would it be wiser to save it in the database? No need to say that we need it to be the most safiest as possible. So maybe an https is required here. But, we what you think is the best way? Maybe other idea? Because in all HTTP case, upload songs (for administration) is quite long and boring, but easly linkable to a song that admin create in his web application comparativly to an FTP application to upload song on server and then list directory in admin part to link the correct uploaded song to the song informations in database. I know that its maybe not quite clear, it's because i'm french but tell me and I will try to explain part that you don't understand.

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• Performance of C# method polymorphism with generics

  - by zildjohn01

  I noticed in C#, unlike C++, you can combine virtual and generic methods. For example: using System.Diagnostics; class Base { public virtual void Concrete() {Debug.WriteLine("base concrete");} public virtual void Generic<T>() {Debug.WriteLine("base generic");} } class Derived : Base { public override void Concrete() {Debug.WriteLine("derived concrete");} public override void Generic<T>() {Debug.WriteLine("derived generic");} } class App { static void Main() { Base x = new Derived(); x.Concrete(); x.Generic<PerformanceCounter>(); } } Given that any number of versions of Generic<T> could be instantiated, it doesn't look like the standard vtbl approach could be used to resolve method calls, and in fact it's not. Here's the generated code: x.Concrete(); mov ecx,dword ptr [ebp-8] mov eax,dword ptr [ecx] call dword ptr [eax+38h] x.Generic<PerformanceCounter>(); push 989A38h mov ecx,dword ptr [ebp-8] mov edx,989914h call 76A874F1 mov dword ptr [ebp-4],eax mov ecx,dword ptr [ebp-8] call dword ptr [ebp-4] The extra code appears to be looking up a dynamic vtbl according to the generic parameters, and then calling into it. Has anyone written about the specifics of this implementation? How well does it perform compared to the non-generic case?

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• OpenMP: Get total number of running threads

  - by Konrad Rudolph

  I need to know the total number of threads that my application has spawned via OpenMP. Unfortunately, the omp_get_num_threads() function does not work here since it only yields the number of threads in the current team. However, my code runs recursively (divide and conquer, basically) and I want to spawn new threads as long as there are still idle processors, but no more. Is there a way to get around the limitations of omp_get_num_threads and get the total number of running threads? If more detail is required, consider the following pseudo-code that models my workflow quite closely: function divide_and_conquer(Job job, int total_num_threads): if job.is_leaf(): # Recurrence base case. job.process() return left, right = job.divide() current_num_threads = omp_get_num_threads() if current_num_threads < total_num_threads: # (1) #pragma omp parallel num_threads(2) #pragma omp section divide_and_conquer(left, total_num_threads) #pragma omp section divide_and_conquer(right, total_num_threads) else: divide_and_conquer(left, total_num_threads) divide_and_conquer(right, total_num_threads) job = merge(left, right) If I call this code with a total_num_threads value of 4, the conditional annotated with (1) will always evaluate to true (because each thread team will contain at most two threads) and thus the code will always spawn two new threads, no matter how many threads are already running at a higher level. I am searching for a platform-independent way of determining the total number of threads that are currently running in my application.

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• Spawning a thread in python

  - by morpheous

  I have a series of 'tasks' that I would like to run in separate threads. The tasks are to be performed by separate modules. Each containing the business logic for processing their tasks. Given a tuple of tasks, I would like to be able to spawn a new thread for each module as follows. from foobar import alice, bob charles data = getWorkData() # these are enums (which I just found Python doesn't support natively) :( tasks = (alice, bob, charles) for task in tasks # Ok, just found out Python doesn't have a switch - @#$%! # yet another thing I'll need help with then ... switch case alice: #spawn thread here - how ? alice.spawnWorker(data) No prizes for guessing I am still thinking in C++. How can I write this in a Pythonic way using Pythonic 'enums' and 'switch'es, and be able to run a module in a new thread. Obviously, the modules will all have a class that is derived from a ABC (abstract base class) called Plugin. The spawnWorker() method will be declared on the Plugin interface and defined in the classes implemented in the various modules. Maybe, there is a better (i.e. Pythonic) way of doing all this?. I'd be interested in knowing

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• Error handling in C++, constructors vs. regular methods

  - by Dennis Ritchie

  I have a cheesesales.txt CSV file with all of my recent cheese sales. I want to create a class CheeseSales that can do things like these: CheeseSales sales("cheesesales.txt"); //has no default constructor cout << sales.totalSales() << endl; sales.outputPieChart("piechart.pdf"); The above code assumes that no failures will happen. In reality, failures will take place. In this case, two kinds of failures could occur: Failure in the constructor: The file may not exist, may not have read-permissions, contain invalid/unparsable data, etc. Failure in the regular method: The file may already exist, there may not be write access, too little sales data available to create a pie chart, etc. My question is simply: How would you design this code to handle failures? One idea: Return a bool from the regular method indicating failure. Not sure how to deal with the constructor. How would seasoned C++ coders do these kinds of things?

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