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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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• 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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• When should we use Views, Temporary Tables and Direct Queries ? What are the Performance issues in a

  - by Shantanu Gupta

  I want to know the performance of using Views, Temp Tables and Direct Queries Usage in a Stored Procedure. I have a table that gets created every time when a trigger gets fired. I know this trigger will be fired very rare and only once at the time of setup. Now I have to use that created table from triggers at many places for fetching data and I confirms it that no one make any changes in that table. i.e ReadOnly Table. I have to use this tables data along with multiple tables to join and fetch result for further queries say select * from triggertable By Using temp table select ... into #tx from triggertable join t2 join t3 and so on select a,b, c from #tx --do something select d,e,f from #tx ---do somethign --and so on --around 6-7 queries in a row in a stored procedure. By Using Views create view viewname ( select ... from triggertable join t2 join t3 and so on ) select a,b, c from viewname --do something select d,e,f from viewname ---do somethign --and so on --around 6-7 queries in a row in a stored procedure. This View can be used in other places as well. So I will be creating at database rather than at sp By Using Direct Query select a,b, c from select ... into #tx from triggertable join t2 join t3 join ... --do something select a,b, c from select ... into #tx from triggertable join t2 join t3 join ... --do something . . --and so on --around 6-7 queries in a row in a stored procedure. Now I can create a view/temporary table/ directly query usage in all upcoming queries. What would be the best to use in this case.

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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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• convert old repository to mercurial

  - by nedlud

  I've been playing around with different versioning systems to find one I'm comfortable with. I started with SVN (lets call this version of the project "f1"), then changed over to GIT. But I didn't know how to convert the old SVN repo to GIT, so I just copied the folder, deleted the .svn stuff, and turned it into a GIT repo (lets call this copied version "f2"). Now I'm playing around with Mercurial and was very pleased to find that it has a Tortoise client for Windows. I was also please to find how easy it was to convert the GIT repo into Mercurial, so I preserved the history (I still cloned it first, just in case. So I'm calling this hg version "f3"). But now what I'm wondering is: what do I do with the old SVN repo that still holds my history from before I played with GIT? I guess I can convert the old SVN repo to Mercurial, but can I then merge those two histories into the one repository so I have a complete set of histories in one place? In other words, can I prepend f1 to f3?

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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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• java : how to handle the design when template methods throw exception when overrided method not throw

  - by jiafu

  when coding. try to solve the puzzle: how to design the class/methods when InputStreamDigestComputor throw IOException? It seems we can't use this degisn structure due to the template method throw exception but overrided method not throw it. but if change the overrided method to throw it, will cause other subclass both throw it. So can any good suggestion for this case? abstract class DigestComputor{ String compute(DigestAlgorithm algorithm){ MessageDigest instance; try { instance = MessageDigest.getInstance(algorithm.toString()); updateMessageDigest(instance); return hex(instance.digest()); } catch (NoSuchAlgorithmException e) { LOG.error(e.getMessage(), e); throw new UnsupportedOperationException(e.getMessage(), e); } } abstract void updateMessageDigest(MessageDigest instance); } class ByteBufferDigestComputor extends DigestComputor{ private final ByteBuffer byteBuffer; public ByteBufferDigestComputor(ByteBuffer byteBuffer) { super(); this.byteBuffer = byteBuffer; } @Override void updateMessageDigest(MessageDigest instance) { instance.update(byteBuffer); } } class InputStreamDigestComputor extends DigestComputor{ // this place has error. due to exception. if I change the overrided method to throw it. evey caller will handle the exception. but @Override void updateMessageDigest(MessageDigest instance) { throw new IOException(); } }

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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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• 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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• 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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• 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 deploy a single webapp with multiple web-modules that may be removed or added individually

  - by Daniel Bleisteiner

  We currently run two separate webapps (WARs) deployed in one single EAR containing additional JARs and settings. To improve our deployment I want to split one of these webapps into different modules that may be build and packaged individually. But I've currently no clue on how to package these modules so that I'm able to add or remove them as desired - at best during runtime. The webapp is getting more and more complex and I'd like to separate some of the functionality into modules. These modules should be packaged as single archives. As long as they contain only classes and resources loaded through code I know how to do this (simple JARs). But how about JSPs? Normally a WAR file contains JSPs or HTML files. I my case it are JSF pages utilizing JBoss Seam and RichFaces. These modules will add classes, resources and JSF pages and other includes to the running webapplication. Is it somehow possible to deploy them as individual archives to serve the same running webapp? We are using Maven for our build and packaging and deploy into JBoss v4.

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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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• 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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• 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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• 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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• Is there a term for this concept, and does it exist in a static-typed language?

  - by Strilanc

  Recently I started noticing a repetition in some of my code. Of course, once you notice a repetition, it becomes grating. Which is why I'm asking this question. The idea is this: sometimes you write different versions of the same class: a raw version, a locked version, a read-only facade version, etc. These are common things to do to a class, but the translations are highly mechanical. Surround all the methods with lock acquires/releases, etc. In a dynamic language, you could write a function which did this to an instance of a class (eg. iterate over all the functions, replacing them with a version which acquires/releases a lock.). I think a good term for what I mean is 'reflected class'. You create a transformation which takes a class, and returns a modified-in-a-desired-way class. Synchronization is the easiest case, but there are others: make a class immutable [wrap methods so they clone, mutate the clone, and include it in the result], make a class readonly [assuming you can identify mutating methods], make a class appear to work with type A instead of type B, etc. The important part is that, in theory, these transformations make sense at compile-time. Even though an ActorModel<T> has methods which change depending on T, they depend on T in a specific way knowable at compile-time (ActorModel<T> methods would return a future of the original result type). I'm just wondering if this has been implemented in a language, and what it's called.

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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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• 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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• IOS : BAD ACCESS when trying to add a new Entity object

  - by Maverick447

  So i'm using coredata to model my relationships . This is the model in brief Type A can have one or more types of type B Type B has a inverse relationship of being associated with one of type A Type B can have one or more types of type C Type C has a inverse relationship of being associated with one of type B From a UI standpoint , I have a Navigation controller with controllers that successively sets up the first A object (VC-1) , then another viewcontroller (VC-2) creates a B object ( I pass in the A object to this controller) and the B object is added to the A object . Similarly the same thing happens with B and C . The third Viewcontroller (VC3) first creates a C object and assigns it to the passed B Object . Also between these viewcontrollers the managedObjectCOntext is also passed . SO my use case is such that while viewcontroller (VC-3) is the top controller a button action will keep creating multiple objects of type C and add them to the same type B object that was passed . Also as part of this function I save the managedObject context after saving each type C . e.g. code in viewcontroller 3 - (void) SaveNewTypeC { TypeC *newtypeC = (Question*)[NSEntityDescription insertNewObjectForEntityForName:@"TypeC" inManagedObjectContext:managedObjectContext]; [newtypeC setProp1:] ; [newtypeC setProp2:] .. .. **[typeBObject addTypeCInTypeBObject:newtypeC];** [section setTotalCObjectCount:[ NSNumber numberWithInt:typeCIndex++]]; NSError *error = nil; if (![managedObjectContext save:&error]) { // Handle error NSLog(@"Unresolved error %@, %@, %@", error, [error userInfo],[error localizedDescription]); exit(-1); // Fail } [newtypeC release]; } - (IBAction)selectedNewButton:(id)sender { [self SaveNewTypeC]; [self startRepeatingTimer]; } The BAD ACCESS seems to appear when the bold line above executes Relating to some HashValue . Any clues on resolving this would be helpful .

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• Unusual heap size limitations in VS2003 C++

  - by Shane MacLaughlin

  I have a C++ app that uses large arrays of data, and have noticed while testing that it is running out of memory, while there is still plenty of memory available. I have reduced the code to a sample test case as follows; void MemTest() { size_t Size = 500*1024*1024; // 512mb if (Size > _HEAP_MAXREQ) TRACE("Invalid Size"); void * mem = malloc(Size); if (mem == NULL) TRACE("allocation failed"); } If I create a new MFC project, include this function, and run it from InitInstance, it works fine in debug mode (memory allocated as expected), yet fails in release mode (malloc returns NULL). Single stepping through release into the C run times, my function gets inlined I get the following // malloc.c void * __cdecl _malloc_base (size_t size) { void *res = _nh_malloc_base(size, _newmode); RTCCALLBACK(_RTC_Allocate_hook, (res, size, 0)); return res; } Calling _nh_malloc_base void * __cdecl _nh_malloc_base (size_t size, int nhFlag) { void * pvReturn; // validate size if (size > _HEAP_MAXREQ) return NULL; ' ' And (size _HEAP_MAXREQ) returns true and hence my memory doesn't get allocated. Putting a watch on size comes back with the exptected 512MB, which suggests the program is linking into a different run-time library with a much smaller _HEAP_MAXREQ. Grepping the VC++ folders for _HEAP_MAXREQ shows the expected 0xFFFFFFE0, so I can't figure out what is happening here. Anyone know of any CRT changes or versions that would cause this problem, or am I missing something way more obvious?

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• Simplification / optimization of GPS track

  - by GreyCat

  I've got a GPS track, produces by gpxlogger(1) (supplied as a client for gpsd). GPS receiver updates its coordinates every 1 second, gpxlogger's logic is very simple, it writes down location (lat, lon, ele) and a timestamp (time) received from GPS every n seconds (n = 3 in my case). After writing down a several hours worth of track, gpxlogger saves several megabyte long GPX file that includes several thousands of points. Afterwards, I try to plot this track on a map and use it with OpenLayers. It works, but several thousands of points make using the map a sloppy and slow experience. I understand that having several thousands of points of suboptimal. There are myriads of points that can be deleted without losing almost anything: when there are several points making up roughly the straight line and we're moving with the same constant speed between them, we can just leave the first and the last point and throw anything else. I thought of using gpsbabel for such track simplification / optimization job, but, alas, it's simplification filter works only with routes, i.e. analyzing only geometrical shape of path, without timestamps (i.e. not checking that the speed was roughly constant). Is there some ready-made utility / library / algorithm available to optimize tracks? Or may be I'm missing some clever option with gpsbabel?

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• Type errors when using same name

  - by lykimq

  I have 3 files: 1) cpf0.ml type string = char list type url = string type var = string type name = string type symbol = | Symbol_name of name 2) problem.ml: type symbol = | Ident of string 3) test.ml open Problem;; open Cpf0;; let symbol b = function | Symbol_name n -> Ident n When I combine test.ml: ocamlc -c test.ml. I received an error: This expression has type Cpf0.name = char list but an expression was expected of type string Could you please help me to correct it? Thank you very much EDIT: Thank you for your answer. I want to explain more about these 3 files: Because I am working with extraction in Coq to Ocaml type: cpf0.ml is generated from cpf.v : Require Import String. Definition string := string. Definition name := string. Inductive symbol := | Symbol_name : name -> symbol. The code extraction.v: Set Extraction Optimize. Extraction Language Ocaml. Require ExtrOcamlBasic ExtrOcamlString. Extraction Blacklist cpf list. where ExtrOcamlString I opened: open Cpf0;; in problem.ml, and I got a new problem because in problem.ml they have another definition for type string This expression has type Cpf0.string = char list but an expression was expected of type Util.StrSet.elt = string Here is a definition in util.ml defined type string: module Str = struct type t = string end;; module StrOrd = Ord.Make (Str);; module StrSet = Set.Make (StrOrd);; module StrMap = Map.Make (StrOrd);; let set_add_chk x s = if StrSet.mem x s then failwith (x ^ " already declared") else StrSet.add x s;; I was trying to change t = string to t = char list, but if I do that I have to change a lot of function it depend on (for example: set_add_chk above). Could you please give me a good idea? how I would do in this case.

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• Visitor Pattern can be replaced with Callback functions?

  - by getit

  Is there any significant benefit to using either technique? In case there are variations, the Visitor Pattern I mean is this: http://en.wikipedia.org/wiki/Visitor_pattern And below is an example of using a delegate to achieve the same effect (at least I think it is the same) Say there is a collection of nested elements: Schools contain Departments which contain Students Instead of using the Visitor pattern to perform something on each collection item, why not use a simple callback (Action delegate in C#) Say something like this class Department { List Students; } class School { List Departments; VisitStudents(Action<Student> actionDelegate) { foreach(var dep in this.Departments) { foreach(var stu in dep.Students) { actionDelegate(stu); } } } } School A = new School(); ...//populate collections A.Visit((student)=> { ...Do Something with student... }); *EDIT Example with delegate accepting multiple params Say I wanted to pass both the student and department, I could modify the Action definition like so: Action class School { List Departments; VisitStudents(Action<Student, Department> actionDelegate, Action<Department> d2) { foreach(var dep in this.Departments) { d2(dep); //This performs a different process. //Using Visitor pattern would avoid having to keep adding new delegates. //This looks like the main benefit so far foreach(var stu in dep.Students) { actionDelegate(stu, dep); } } } }

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• Is there a Scala version of .irbrc or another way to define some default libraries for REPL use?

  - by Tom Morris

  I've written a little library that uses implicits to add functionality that one only needs when using the REPL in Scala. Ruby has libraries like this - for things like pretty printing, firing up text editors (like the interactive_editor gem which invokes Vim from irb - see this post), debuggers and the like. The library I am trying to write adds some methods to java.lang.Class and java.lang.reflect classes using the 'pimp my library' implicit conversion process to help you go and find documentation (initially, with Google, then later possibly with a JavaDoc/ScalaDoc viewer, and maybe the StackOverflow API eventually!). It's an itch-scratching library: I spend so much time copying and pasting classnames into Google that I figured I may as well automate the process. It is the sort of functionality that developers will want to add to their system for use only in the REPL - they shouldn't really be adding it to projects (partly because it may not be something that their fellow developers want, but also because if you are doing some exploratory development, it may be with just a Scala REPL that's not being invoked by an IDE or build tool). In my case, I want to include a few classes and set up some implicits - include a .jar on the CLASSPATH and import it, basically. In Ruby, this is the sort of thing that you'd add to your .irbrc file. Other REPLs have similar ways of setting options and importing libraries. Is there a similar file or way of doing this for the Scala REPL?

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