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• How to solve generic algebra using solver/library programmatically? Matlab, Mathematica, Wolfram etc?

  - by DevDevDev

  I'm trying to build an algebra trainer for students. I want to construct a representative problem, define constraints and relationships on the parameters, and then generate a bunch of Latex formatted problems from the representation. As an example: A specific question might be: If y < 0 and (x+3)(y-5) = 0, what is x? Answer (x = -3) I would like to encode this as a Latex formatted problem like. If $y<0$ and $(x+constant_1)(y+constant_2)=0$ what is the value of x? Answer = -constant_1 And plug into my problem solver constant_1 > 0, constant_1 < 60, constant_1 = INTEGER constant_2 < 0, constant_2 > -60, constant_2 = INTEGER Then it will randomly construct me pairs of (constant_1, constant_2) that I can feed into my Latex generator. Obviously this is an extremely simple example with no real "solving" but hopefully it gets the point across. Things I'm looking for ideally in priority order * Solve algebra problems * Definition of relationships relatively straight forward * Rich support for latex formatting (not just writing encoded strings) Thanks!

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• FileReference.save() duplicates ByteArray

  - by bartekb

  Hi, I've encountered a memory problem using FileReference.save(). My Flash application generates of a lot of data in real-time and needs to save this data to a local file. As I understand, Flash 10 (as opposed to AIR) does not support streaming to a file. But, what's even worse is that FileReference.save() duplicates all the data before saving it. I was looking for a workaround to this doubled memory usage and thought about the following approach: What if I pass a custom subclass of ByteArray as an argument to FileReference.save(), where this ByteArray subclass would override all read*() methods. The overridden read*() methods would wait for a piece of data to be generated by my application, return this piece of data and immediately remove it from the memory. I know how much data will be generated, so I could also override length/bytesAvailable methods. Would it be possible? Could you give me some hint how to do it? I've created a subclass of ByteArray, registered an alias for it, passed an instance of this subclass to FileReference.save(), but somehow FileReference.save() seems to treat it just as it was a ByteArray instance and doesn't call any of my overridden methods... Thanks a lot for any help!

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• Scala newbie vproducer/consumer attempt running out of memory

  - by Nick

  I am trying to create a producer/consumer type Scala app. The LoopControl just sends a message to the MessageReceiver continually. The MessageReceiver then delegates work to the MessageCreatorActor (whose work is to check a map for an object, and if not found create one and start it up). Each MessageActor created by this MessageCreatorActor is associated with an Id. Eventually this is where I want to do business logic. But I run out of memory after 15 minutes. Its finding the cached actors,but quickly runs out of memory. Any help is appreciated. Or any one has any good code on producers consumers doing real stuff (not just adding numbers), please post. import scala.actors.Actor import java.util.HashMap import scala.actors.Actor._ case object LoopControl case object MessageReceiver case object MessageActor case object MessageActorCreator class MessageReceiver(msg: String) extends Actor { var messageActorMap = new HashMap[String, MessageActor] val messageCreatorActor = new MessageActorCreator(null, null) def act() { messageCreatorActor.start loop { react { case MessageActor(messageId) => if (msg.length() > 0) { var messageActor = messageActorMap.get(messageId); if(messageActor == null) { messageCreatorActor ! MessageActorCreator(messageId, messageActorMap) }else { messageActor ! MessageActor } } } } } } case class MessageActorCreator(msg:String, messageActorMap: HashMap[String, MessageActor]) extends Actor { def act() { loop { react { case MessageActorCreator(messageId, messageActorMap) => if(messageId != null ) { var messageActor = new MessageActor(messageId); messageActorMap.put(messageId, messageActor) println(messageActorMap) messageActor.start messageActor ! MessageActor } } } } } class LoopControl(messageReceiver:MessageReceiver) extends Actor { var count : Int = 0; def act() { while (true) { messageReceiver ! MessageActor ("00-122-0X95-FEC0" + count) //Thread.sleep(100) count = count +1; if(count > 5) { count = 0; } } } } case class MessageActor(msg: String) extends Actor { def act() { loop { react { case MessageActor => println() println("MessageActor: Got something-> " + msg) } } } } object messages extends Application { val messageReceiver = new MessageReceiver("bootstrap") val loopControl = new LoopControl(messageReceiver) messageReceiver.start loopControl.start }

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• Javascript JQUERY AJAX: When Are These Implemented

  - by Michael Moreno

  I'm learning javascript. Poked around this excellent site to gather intel. Keep coming across questions / answers about javascript, JQUERY, JQUERY with AJAX, javascript with JQUERY, AJAX alone. My conclusion: these are all individually powerful and useful. My confusion: how does one determine which/which combination to use ? I've concluded that javascript is readily available on most browsers. For example, I can extend a simple HTML page with <html> <body> <script type="text/javascript"> document.write("Hello World!"); </script> </body> </html> However, within the scope of Python/DJANGO, many of these questions are JQUERY and AJAX related. At which point or under what development circumstances would I conclude that javascript alone isn't going to "cut it", and I need to implement JQUERY and/or AJAX and/or some other permutation ?

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• not able to run c/cpp execs in eclipse cdt

  - by user1658323

  i installed eclipse and then cdt on an ubuntu system recently and was trying to make the first runnable c/c++ proj.. i installed g++ also, and then created the first executable cpp 'Hello World' project some files are created... then some issues... 1) even though Build Automatically is selected, I have to goto the project n do a Build Project to build it manually, and this i have to do everytime i make a change 2) After Building manually, there are some new folders created with Binaries and Debug files and i can see g++ commands in the console being executed. The project binary is output both to debug n binaries folder. But i am not able to run these through the Green Play Button or any other way in eclipse. Even Run configuration is not showing any option for c/C++ proj.. though i can goto terminal and run the binary myself through ./ But i want to be able to run n debug this through eclipse. plz help in fixing me this problem as i really love eclipse n have some c/cpp assignments coming soon.. Console info on doing a manual project build - Build of configuration Debug for project qwe ** make all Building file: ../src/qwe.cpp Invoking: GCC C++ Compiler g++ -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/qwe.d" -MT"src/qwe.d" -o "src/qwe.o" "../src/qwe.cpp" Finished building: ../src/qwe.cpp Building target: qwe Invoking: GCC C++ Linker g++ -o "qwe" ./src/qwe.o Finished building target: qwe Build Finished **

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• Am I going the right way to make login system secure with this simple password salting?

  - by LoVeSmItH

  I have two fields in login table password salt And I have this little function to generate salt function random_salt($h_algo="sha512"){ $salt1=uniqid(rand(),TRUE); $salt2=date("YmdHis").microtime(true); if(function_exists('dechex')){ $salt2=dechex($salt2); } $salt3=$_SERVER['REMOTE_ADDR']; $salt=$salt1.$salt2.$salt3; if(function_exists('hash')){ $hash=(in_array($h_algo,hash_algos()))?$h_algo:"sha512"; $randomsalt=hash($hash,md5($salt)); //returns 128 character long hash if sha512 algorithm is used. }else{ $randomsalt=sha1(md5($salt)); //returns 40 characters long hash } return $randomsalt; } Now to create user password I have following $userinput=$_POST["password"] //don't bother about escaping, i have done it in my real project. $static_salt="THIS-3434-95456-IS-RANDOM-27883478274-SALT"; //some static hard to predict secret salt. $salt=random_salt(); //generates 128 character long hash. $password =sha1($salt.$userinput.$static_salt); $salt is saved in salt field of database and $password is saved in password field. My problem, In function random_salt(), I m having this FEELING that I'm just making things complicated while this may not generate secure salt as it should. Can someone throw me a light whether I m going in a right direction? P.S. I do have an idea about crypt functions and like such. Just want to know is my code okay? Thanks.

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• Print an array elements

  - by 1ace1

  Hello guys, this is my first post and im still a beginner in the programming world so bare with me. I just created an array with 100 initialized values and i want to print out 10 elements on each line so it would be somthing like this 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 ...26 this is the code i used and i managed to do it for the first 10 elements but i couldnt figure out how to do it for the rest public static void main(String[] args) { int[] numbers = { 0,1,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17}; int i, count = 0; for (i = 0; i < numbers.length; i++) { System.out.print(numbers[i] + " "); count++; if (count == 9) for (i = 9; i < numbers.length; i++) System.out.println(numbers[i] + " "); } } thanks!

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• Java object graph -> xml when direction of object association needs to be reversed.

  - by Sigmoidal

  An application I have been working on has objects with a relationship similar to below. In the real application both objects are JPA entities. class Underlying{} class Thing { private Underlying underlying; public Underlying getUnderlying() { return underlying; } public void setUnderlying(final Underlying underlying) { this.underlying = underlying; } } There is a requirement in the application to create xml of the form: <template> <underlying> <thing/> <thing/> <thing/> </underlying> </template> So we have a situation where the object graph expresses the relationship between Thing and Underlying in the opposite direction to how it's expressed in the xml. I expect to use JAXB to create the xml but ideally I don't want to have to create a new object hierarchy to reflect the associations in the xml. Is there any way to create xml of the form required from the entities in their current form (through the use of xml annotations or something)? I don't have any experience using JAXB but from the limited research I've done it doesn't seem like it's possible to reverse the direction of association in any straightforward way. Any help/advice would be greatly appreciated. One other option that has been suggested is to use XLST to transform the xml into the correct format. I have done no research on this topic as yet but I'll add to the question when I have some more info. Thanks, Matt.

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• Django: Paginator + raw SQL query

  - by Silver Light

  Hello! I'm using Django Paginator everywhere on my website and even wrote a special template tag, to make it more convenient. But now I got to a state, where I need to make a complex custom raw SQL query, that without a LIMIT will return about 100K records. How can I use Django Pagintor with custom query? Simplified example of my problem: My model: class PersonManager(models.Manager): def complicated_list(self): from django.db import connection #Real query is much more complex cursor.execute("""SELECT * FROM `myapp_person`"""); result_list = [] for row in cursor.fetchall(): result_list.append(row[0]); return result_list class Person(models.Model): name = models.CharField(max_length=255); surname = models.CharField(max_length=255); age = models.IntegerField(); objects = PersonManager(); The way I use pagintation with Django ORM: all_objects = Person.objects.all(); paginator = Paginator(all_objects, 10); try: page = int(request.GET.get('page', '1')) except ValueError: page = 1 try: persons = paginator.page(page) except (EmptyPage, InvalidPage): persons = paginator.page(paginator.num_pages) This way, Django get very smart, and adds LIMIT to a query when executing it. But when I use custom manager: all_objects = Person.objects.complicated_list(); all data is selected, and only then python list is sliced, which is VERY slow. How can I make my custom manager behave similar like built in one?

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• Telerik RadGrid: grid clientside pagination

  - by ram

  I have a web service which returns me some data,I am massaging this data and using this as datasource for my radgrid (telerik). The datasource is quite large, and would like to paginate it. I found couple of problems when I paginate it in the server side I have to bind the grid again for pagination, which essentially means I have to make a call to WS again to get the data. This is an expensive call for me. I would rather forgo the benefits of pagination and would display all the results in the same page, except for it would be a bit clumsy During the postback RadGrid1.Items.Count happens to be the number of items getting paginated (25- in my case) which is expected as all the items in the datasource are not getting bound. This of course is not an issue. The real issue is that we have some checkboxes which get checked based on some business condition. We add this to our business object/DB later. So if the user has not navigated all the pages, these "checked" items do not get added as pagination limits the "Items" in the grid to those which get bound for that particular page index. My Thoughts: I would rather have some sort of client side pagination, where we can hide/show contents than going to the server and doing a databind every time. Though it will return all the results, the UI will not be clumsy and the grid would have "all the items" during postback Is there a way to do it ? If it were a regular asp.net gridView, can someone point me to a good article which would serve my purpose Ram PS: who else think radgrid is crazy ? (unfortunately I did not make this choice)

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• Refactoring or Rewriting Monolithic PHP Spaghetti Codebase

  - by nategood

  I've inherited a really poorly designed PHP spaghetti code project. It's been gaining a good bit of traffic recently and is starting to have performance issues on top of the poor monolithic code base. Its maxing out performance on a chunky 16GB dedicated machine when it really shouldn't be. I'm planning on doing some performance tweaks right off the bat to help the performance issue, but this still won't really help the horrible code base. The team is small but expecting to grow very soon. I've read Joel's article on the troubles of doing a complete rewrite and see the concerns. But how bad does the code base have to be before you consider a rewrite? There is PHP handling logic interjected into what one would usually consider a "view". Even worse, in some places SQL statements are in these same files! The only real separation of presentation and logic are a few PHP scripts that serve as function libraries. These scripts do most of the ORM stuff... if you can even call it that. Trying to slowly refractor this seems like a nightmare. Open to your thoughts and opinions... however not interested in hearing, "Run away, Run away!".

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• How do you prove a function works?

  - by glenn I.

  I've recently gotten the testing religion and have started primarily with unit testing. I code unit tests which illustrate that a function works under certain cases, specifically using the exact inputs I'm using. I may do a number of unit tests to exercise the function. Still, I haven't actually proved anything other than the function does what I expect it to do under the scenarios I've tested. There may be other inputs and scenarios I haven't thought of and thinking of edge cases is expensive, particularly on the margins. This is all not very satisfying to do me. When I start to think of having to come up with tests to satisfy branch and path coverage and then integration testing, the prospective permutations can become a little maddening. So, my question is, how can one prove (in the same vein of proving a theorem in mathematics) that a function works (and, in a perfect world, compose these 'proofs' into a proof that a system works)? Is there a certain area of testing that covers an approach where you seek to prove a system works by proving that all of its functions work? Does anybody outside of academia bother with an approach like this? Are there tools and techniques to help? I realize that my use of the word 'work' is not precise. I guess I mean that a function works when it does what some spec (written or implied) states that it should do and does nothing other than that. Note, I'm not a mathematician, just a programmer.

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• Code Golf: Find the possible ways on a numpad

  - by ikar

  I was bored today at school and so I tried to amuse myself using my calculator and a "game" I've invented which isn't really a game but keeps the boringness away. Also some time has passed since the last real code-golf here, so I decided to create this one. Imagine a simplified numpad like you know it from your phone (I'll leave the 0 out for this code-golf as it kinda destroys all the fun) 1 2 3 4 5 6 7 8 9 Now the rules of the game were always: At the end every digit must have been visited exactly once You can start at any digit you want You can always move one digit up, down, left or right. You can't move diagonally! There a quite a lot of possible ways (or not; I haven't found out yet), here some trivial examples: > > v v < < > > | The output of the golf-program should look something like the above, I'll try to explain: Symbols: Go right < Go left ^ Go up v Go down | End of the way Example solutions: (Program output can either be the numbers pressed in the right order from beginning point to end, or an (ASCII) picture like above) 147852369 569874123 523698741 So if we speak out the example above it would be: Start at 1, move right to 2, move right to 3, go down to 6, go left to 5, go left to 4, go down to 7, go right to 8 then go right to 9 and we are finished! Now there are many different ways possible: You could as well start at 5 and go around it in a circle. So the task would be: Write a program that can compute (using brute-force or whatever) the possible solutions for the numpad problem described above. (Friendly rethorical question with smiley removed because it made some people think that this is homework)

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• How would I go about sharing variables in a C++ class with Lua?

  - by Nicholas Flynt

  I'm fairly new to Lua, I've been working on trying to implement Lua scripting for logic in a Game Engine I'm putting together. I've had no trouble so far getting Lua up and running through the engine, and I'm able to call Lua functions from C and C functions from Lua. The way the engine works now, each Object class contains a set of variables that the engine can quickly iterate over to draw or process for physics. While game objects all need to access and manipulate these variables in order for the Game Engine itself to see any changes, they are free to create their own variables, a Lua is exceedingly flexible about this so I don't forsee any issues. Anyway, currently the Game Engine side of things are sitting in C land, and I really want them to stay there for performance reasons. So in an ideal world, when spawning a new game object, I'd need to be able to give Lua read/write access to this standard set of variables as part of the Lua object's base class, which its game logic could then proceed to run wild with. So far, I'm keeping two separate tables of objects in place-- Lua spawns a new game object which adds itself to a numerically indexed global table of objects, and then proceeds to call a C++ function, which creates a new GameObject class and registers the Lua index (an int) with the class. So far so good, C++ functions can now see the Lua object and easily perform operations or call functions in Lua land using dostring. What I need to do now is take the C++ variables, part of the GameObject class, and expose them to Lua, and this is where google is failing me. I've encountered a very nice method here which details the process using tags, but I've read that this method is deprecated in favor of metatables. What is the ideal way to accomplish this? Is it worth the hassle of learning how to pass class definitions around using libBind or some equivalent method, or is there a simple way I can just register each variable (once, at spawn time) with the global lua object? What's the "current" best way to do this, as of Lua 5.1.4?

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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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• what use does the javascript forEach method have (that map can't do)?

  - by JohnMerlino

  Hey all, The only difference I see in map and foreach is that map is returning an array and foreach is not. However, I don't even understand the last line of the foreach method "func.call(scope, this[i], i, this);". For example, isn't "this" and "scope" referring to same object and isn't this[i] and i referring to the current value in the loop? I noticed on another post someone said "Use forEach when you want to do something on the basis of each element of the list. You might be adding things to the page, for example. Essentially, it's great for when you want "side effects". I don't know what is meant by side effects. Array.prototype.map = function(fnc) { var a = new Array(this.length); for (var i = 0; i < this.length; i++) { a[i] = fnc(this[i]); } return a; } Array.prototype.forEach = function(func, scope) { scope = scope || this; for (var i = 0, l = this.length; i < l; i++) func.call(scope, this[i], i, this); } Finally, are there any real uses for these methods in javascript (since we aren't updating a database) other than to manipulate numbers like this: alert([1,2,3,4].map(function(x){ return x + 1})); //this is the only example I ever see of map in javascript. Thanks for any reply.

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• How can someone with no experience learn how to program?

  - by Mugatu

  A friend and I have been coming up with website ideas for a couple years, mostly just jotting them down whenever we come up with a good, useful idea when browsing the web. For the past 6 months we've hired a couple different programmers to make a couple of the sites for us, but have been disappointed with how it's gone. Been too slow and too many miscommunications for our liking. So like the saying goes if you want something done right do it yourself, we're going to do it ourselves. I know nothing about programming, I've never written a line of code in my life. I consider myself very good with math and about as logical as you can get, but I have zero real-life programming knowledge. The sites we want to make are all pretty 'Web 2.0'ish', meaning user-generated content, commenting on posts, pages that change on the fly, etc. So here are some of my questions for anyone who's been there before: Is there a language you'd recommend learning first? Something that is a good indicator how most other languages work? What web programming languages do you recommend learning first based on popularity both now and the future. I don't want to learn a language that's going to be outdated by the time I'm an expert at it. Any specific books you'd recommend? Any general advice you'd give to someone literally starting at square zero for coding who plans on being in it for the long haul?

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• Best practice to test a web application, regarding domain name and integration with external service

  - by ycseattle

  I have run into these problems several times and was never able to find a comfortable solution. Let's say my website has the domain name MyDomain.com. When I run the tests on the test machine (a continuous integration server), I will modify the HOSTS file on this machine so the MyDomain.com is mapped to this local machine instead of the real production server. This doesn't work very well for many situations. For example, my application will create subdomain names user1.MyDomain.com dynamically but this is difficult to keep the testing flexible. Another problem is my web application will interact with Amazon S3, and sometimes other service like Amazon Simple Message Queue. I am only comfortable to include these interaction in my tests but I am never happy with my solution for mixing testing and production on Amazon services. Could somebody offer some tips on these issues? I would like to make my testing framework clean and flexible. I am sure this is a common question for all web applications and there must be a mature way to deal with these. Thanks!

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• How do I search & replace all occurrences of a string in a ms word doc with python?

  - by Mark

  Hello there, I am pretty stumped at the moment. Based on http://stackoverflow.com/questions/1045628/can-i-use-win32-com-to-replace-text-inside-a-word-document I was able to code a simple template system that generates word docs out of a template word doc (in Python). My problem is that text in "Text Fields" is not find that way. Even in Word itself there is no option to search everything - you actually have to choose between "Main Document" and "Text Fields". Being new to the Windows world I tried to browse the VBA docs for it but found no help (probably due to "text field" being a very common term). word.Documents.Open(f) wdFindContinue = 1 wdReplaceAll = 2 find_str = '\{\{(*)\}\}' find = word.Selection.Find find.Execute(find_str, False, False, True, False, False, \ True, wdFindContinue, False, False, False) while find.Found: t = word.Selection.Text.__str__() r = process_placeholder(t, answer_data, question_data) if type(r) == dict: errors.append(r) else: find.Execute(t, False, True, False, False, False, \ True, False, False, r, wdReplaceAll) This is the relevant portion of my code. I was able to get around all problems by myself by now (hint: if you want to replace strings with more than 256 chars, you have to do it via clipboard, etc ...) Hope, someone can help me.

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• C++ casted realloc causing memory leak

  - by wyatt

  I'm using a function I found here to save a webpage to memory with cURL: struct WebpageData { char *pageData; size_t size; }; size_t storePage(void *input, size_t size, size_t nmemb, void *output) { size_t realsize = size * nmemb; struct WebpageData *page = (struct WebpageData *)output; page->pageData = (char *)realloc(page->pageData, page->size + realsize + 1); if(page->pageData) { memcpy(&(page->pageData[page->size]), input, realsize); page->size += realsize; page->pageData[page->size] = 0; } return realsize; } and find the line: page->pageData = (char *)realloc(page->pageData, page->size + realsize + 1); is causing a memory leak of a few hundred bytes per call. The only real change I've made from the original source is casting the line in question to a (char *), which my compiler (gcc, g++ specifically if it's a c/c++ issue, but gcc also wouldn't compile with the uncast statement) insisted upon, but I assume this is the source of the leak. Can anyone elucidate? Thanks

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• How should rules for Aggregate Roots be enforced?

  - by MylesRip

  While searching the web, I came across a list of rules from Eric Evans' book that should be enforced for aggregates: The root Entity has global identity and is ultimately responsible for checking invariants Root Entities have global identity. Entities inside the boundary have local identity, unique only within the Aggregate. Nothing outside the Aggregate boundary can hold a reference to anything inside, except to the root Entity. The root Entity can hand references to the internal Entities to other objects, but they can only use them transiently (within a single method or block). Only Aggregate Roots can be obtained directly with database queries. Everything else must be done through traversal. Objects within the Aggregate can hold references to other Aggregate roots. A delete operation must remove everything within the Aggregate boundary all at once When a change to any object within the Aggregate boundary is committed, all invariants of the whole Aggregate must be satisfied. This all seems fine in theory, but I don't see how these rules would be enforced in the real world. Take rule 3 for example. Once the root entity has given an exteral object a reference to an internal entity, what's to keep that external object from holding on to the reference beyond the single method or block? (If the enforcement of this is platform-specific, I would be interested in knowing how this would be enforced within a C#/.NET/NHibernate environment.)

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• What can i use to journal writes to file system

  - by Dmitry

  Hello, all I need to track all writes to files in order to have synchronized version of files on different place (server or just other directory, not considerable). Let it: all files located in same directory feel free to create some system files (e.g. SomeFileName.Ext~temp-data) no one have concurrent access to synced directory; nobody spoil ours meta-files or change real-files before we do postponed writes (like a commits) do not to care recovering "local" changes in case of crash; system can just rolled back to state of "server" by simple copy from it significant to have it transparent to use (so programmer must just call ordinary fopen(), read(), write()) It must be guaranteed that copy of files which "server" have is consistent. That is whole files scope existed in some moment of time. They may be sufficiently outdated but it must be fair snapshot of all files at some time. As i understand i should overload writing logic to collect data in order sent changes to "server". For example writing to temporary File~tmp. And so i have to overload reads in order program could read actual data of file. It would be great if you suggest some existing library (java or c++, it is unimportant) or solution (VCS customizing?). Or give hints how should i write it by myself. edit: After some reading i have more precision requirements: I need COW (Copy-on-write) wrapper for fopen(),fwrite(),.. or interceptor (hook) WriteFile() and other FS api system calls. Log-structured file system in userspace would be a alternative too.

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• where does a novice begin with error logging in asp.net c# ?

  - by korben

  i'm a novice teaching myself asp.net in c# via trial and error learn by doing, unfortunately this means lots of errors! i have a custom errors page now that is basically a 404 so that site visitors don't get that ugly application error message .NET throws, but i WOULD like to be able to see what's going wrong myself as people use the site. so i'm looking to build or learn from a fairly basic error logging c# class, that will send the same information given in a browser when hitting a .NET error, send this into a TXT file and email me the error at the same time would be great i don't know where to even begin, can someone give me some pointers? an open source class that does this already that i could plugin and play with would work as well. otherwise some links or guidance on where to start reading would be great too. i sort of have a mental block on understand msdn info-dump pages though, i'm hoping to find some articles on real people talking about implementing the same thing themselves or something like that please note i'm not looking to use some extensive or complicated third party service for this, i'm hoping to learn from the process of implementing a concise customized one

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• Is there a way to force ContourPlot re-check all the points on the each stage of it's recursion algorithm?

  - by Alexey Popkov

  Hello, Thanks to this excellent analysis of the Plot algorithm by Yaroslav Bulatov, I now understand the reason why Plot3D and ContourPlot fail to draw smoothly functions with breaks and discontinuities. For example, in the following case ContourPlot fails to draw contour x^2 + y^2 = 1 at all: ContourPlot[Abs[x^2 + y^2 - 1], {x, -1, 1}, {y, -1, 1}, Contours -> {0}] It is because the algorithm does not go deeply into the region near x^2 + y^2 = 1. It "drops" this region on an initial stage and do not tries to investigate it further. Increasing MaxRecursion does nothing in this sense. And even undocumented option Method -> {Refinement -> {ControlValue -> .01 \[Degree]}} does not help (but makes Plot3D a little bit smoother). The above function is just a simple example. In real life I'm working with very complicated implicit functions that cannot be solved analytically. Is there a way to get ContourPlot to go deeply into such regions near breaks and discontinuities?

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• How to prevent the user from leaving the page

  - by JohnathanKong

  Hey Everyone, I am currently building a registration site where if the user leaves, I want to pop up a CSS box asking him if he is sure or not. I can accomplish this feat using confirm boxes, but the client says that they are too ugly. I've tried using unload and beforeunload, but both cannot stop the page from being redirected. Using those to events, I return false, so maybe there's a way to cancel other than returning false? Another solution that I've had was redirecting them to another page that has my popup, but the problem with that is that if they do want to leave the page, and it wasn't a mistake, they lose the page they were originally trying to go to. If I was a user, that would irritate me. The last solution was real popup window. The only thing I don't like about that is that the main winow will have their destination page while the pop will have my page. In my opinion it looks disjoint. On top of that, I'd be worried about popup blockers.

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