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• Free libraries to work with Excel

  - by Danil Gholtsman

  I got some excel files, I need to read data from it and upload data to some database (I need to use firebird, but whatever). Right now I use <QAxObject> from Qt and code look like QAxObject* excel = new QAxObject("Excel.Application"); //pointer to excel //excel->setProperty("Visible", false); QAxObject* workbooks = excel->querySubObject("WorkBooks"); //get pointer to booklist workbooks->dynamicCall("Open (const QString&)", QString("C:\\databases\\test.xls")); //opening file, getting pointer to booklist QAxObject* workbook = excel->querySubObject("ActiveWorkBook"); QAxObject* worksheets = workbook->querySubObject("WorkSheets"); etc. The problem is that this way on users PC there must be installed Excel. Is there exists some free C++ libraries to work with *.xls, *.xlsx files without Excel installed?

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• newbie in c and issue with integers [migrated]

  - by user2527918

  // // main.c // cmd4 // // Created by Kevin Rudd on 27/06/13. // Copyright (c) 2013 Charlie Brown. All rights reserved. // #include <stdio.h> int main(int argc, const char * argv[]) { int x =10, y =20, b = 500; int z = x*y; int f = z/b; // insert code here... printf("x is:%d, y is:%d, b is %d\n",x,y,b); printf("x times y is: %d\n",z); printf("z divided by b is: %d\n",f); return 0; } on print out f = 0. Why?

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• Inventory Item Exist checker

  - by Annalyne

  I have a question regarding declaring my inventory. I made it a string named inventory, with a constant number as its max value. The thing is, I want the user to use an item if he / she gains an item. The problem is, I do not know what syntax should I use to determine if the user has an item and use that item. Here's my code I just started: so declaring the inventory: const int MAX_ITEMS = 15; string game_inventory [MAX_ITEMS]; int itemnum = 0; I have some items like potion, antidote, gems and others. I use the: game_inventory[itemnum++] = "Potion" to place items in my inventory. If I want to use the potion, IF I HAVE one, how can i make a function to check whether I have a potion or anything and use it?

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• Problem playing repeat animation/action?

  - by Beast

  I'm calling this function on multiple sprites after checking numberOfRunningActions()"to play same animation but it's not working only the first tagged sprite plays the animation. What am I doing wrong? void CGame::playAnimation(const char* filename, int tag, CCLayer* target) { CCAnimation* animation = CCAnimation::animation(); CCSprite* spriteSheet = CCSprite::spriteWithFile(filename); for(int i = 0; i < spriteSheet->getTexture()->getPixelsWide()/SIZE; i++) // SIZE is an int value { animation->addFrameWithTexture(spriteSheet->getTexture(), CCRect(SIZE * i, 0, SIZE, SIZE)); } CCActionInterval* action = CCAnimate::actionWithDuration(1, animation, true); CCRepeatForever* repeatAction = CCRepeatForever::actionWithAction(action); target->getChildByTag(tag)->runAction(repeatAction); }

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• is this the correct way to use glTexCoordPointer?

  - by RubyKing

  Hey all Just trying to work out how to use this function glTexCoordPointer. Here is the man pages http://www.opengl.org/sdk/docs/man/xhtml/glTexCoordPointer.xml which states that I must set a pointer to the first element of the array that uses the texture cordinate. Here is my array static const GLfloat GUIVertices[] = { //FIRST QUAD 1.0f, 1.0f, 0.0f, 1.0f, 1.0f, 0.0f, -1.0f, 1.0f, 0.0f, 1.0f, 0.0f, 0.0f, -1.0f, 0.94f, 0.0f, 1.0f, 0.0f, 1.0f, 1.0f, 0.94f, 0.0f, 1.0f, 1.0f, 1.0f, //2ND QUAD // x y z w X Y 1.0f, -1.0f, 0.0f, 1.0f, 1.0f, 0.0f, -1.0f,-1.0f, 0.0f, 1.0f, 0.0f, 0.0f, -1.0f,-0.94f, 0.0f,1.0f, 0.0f, 1.0f, 1.0f, -0.94f, 0.0f,1.0f, 1.0f, 1.0, }; But how do I set the pointer correctly? like this glTexCoordPointer(1, GL_FLOAT, 6, reinterpret_cast(29 * sizeof(float)) ); for the fifth element on the 2nd quad first row. any help is thankful

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• Triangles in a C++ STL Vector as an Objective-C member sometimes draws incorrectly in OpenGL ES

  - by Rahil627

  The polygons draw correctly 80% of the time. When it fails, a vertex is dislocated. The polygon is consistently drawn with the wrong vertex. I checked that the vector is correct during initialization, even when it's wrongly drawn. I'm using Cocos2d. The class member: @interface Polygon : CCSprite { std::vector<float> triangleVertices; } The draw function called in [Polygon draw]: + (void)drawTrianglesWithVertices:(const std::vector<float> &)v { //glEnableClientState(GL_VERTEX_ARRAY); glDisable(GL_TEXTURE_2D); glDisableClientState(GL_TEXTURE_COORD_ARRAY); glDisableClientState(GL_COLOR_ARRAY); glVertexPointer(2, GL_FLOAT, 0, &v[0]); glDrawArrays(GL_TRIANGLES, 0, v.size()); //glDisableClientState(GL_VERTEX_ARRAY); glEnableClientState(GL_COLOR_ARRAY); glEnableClientState(GL_TEXTURE_COORD_ARRAY); glEnable(GL_TEXTURE_2D); } Any ideas?

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• Whether to use -pedantic flag in g++ or not?

  - by user803563

  I'm learning C++ and I'm using g++ on Linux for practicing. 1) I want to know if people working as programmers use g++ -pedantic flag and also it's importance in real world. 2) What about other compilers, do they also allow this? Has this become some de-facto standard? I'm interested because I'm reading C++ Primer where the author points that its illegal to use non-const expression as dimension in array definition and g++ by default allows it. And there might be other things I'm unaware of.

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• Storing and reading file paths from _TCHAR *argv[]

  - by ArsenArsen

  How to convert from _TCHAR* to "" and to keep all : and /? I tried: int _tmain(int argc, _TCHAR* argv[]) { if(!argv[1]){ std::cout<<"No Variables.\r\n"; system("PAUSE"); return 0; std::exit; } std::cout<<"Path: "<<argv[1]<<"\r\n"; system("PAUSE"); return 0; } But, output is either "No variables." or "Path: C" (when I changed _TCHAR to const char and char) or either "Path: 00038706"

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• What is wrong with this code for reading binary files? [on hold]

  - by qed

  What is wrong with this code for reading binary files? It compiles OK, but will not print out the file as planned, in fact, it prints nothing at all. #include <iostream> #include <fstream> int main(int argc, const char *argv[]) { if (argc < 2) { ::std::cerr << "usage: " << argv[0] << " <filename>\n"; return 1; } ::std::basic_ifstream<unsigned char> in(argv[1], ::std::ios::binary); unsigned char uc; while (in.get(uc)) { printf("%02X ", uc); } // TODO: error handling, in case the file could not be opened or read return 0; }

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• Personal Technology – Excel Tip: Comparing Excel Files

  - by Pinal Dave

  This guest post is by Vinod Kumar. Vinod Kumar has worked with SQL Server extensively since joining the industry over a decade ago. Working on various versionsfrom SQL Server 7.0, Oracle 7.3 and other database technologies – he now works with the Microsoft Technology Center (MTC) as a Technology Architect. Let us read the blog post in Vinod’s own voice. I have been writing about Excel Tips over my blog and thought it would be great to share one interesting tips here as a guest blog here. Assume a situation where you want to compare multiple excel files. Here is a typical scenario I have encountered as a common activity. Assume you are sending an Excel file with tons of data, formulae and multiple sheets. Now you are requesting your colleague to validate the file and if required change content for correctness. After receiving the file from your colleague, now you want to know what changes were made by this person to your document. Now here is a cool new addition to Excel 2013 that can help you achieve this task. To get to this option, click the INQUIRE Tab. Incase you don’t have the INQUIRE Tab, check Options using INQUIRE blog. In that post, we discuss all the other options of INQUIRE tab. Once you are on the INQUIRE Tab, select “Compare Files” button as shown in the figure above. This brings a dialog as below. If you are on Windows 8 or Windows 7 OS, search for an application called “Spreadsheet Compare 2013”. Ultimately both the options lead us to the same application. If you are using the stand alone app, once the App initializes, click the “Compare files” options from the toolbar. Make sure to give two different Excel files as shown in the figure above. After selecting the Excel Sheets, you can see the Compare tool has a number of other options to play from. We will talk about some of them later in this post. Just below our toolbar is a colorful side-by-side comparison of both our excel sheets. We can also see the various Tab’s from each file. There is a meaning for each of our color coding which will be discussed next. As you saw above, the color coding has a meaning. For example the bottom pane lists each of the color coding and most importantly each of the changes as compared side-by-side. The detailed information shown below can be exported using the “Export Results” options from the toolbar as a separate Excel Workbook or can be copied to clipboard to be used later. The final piece of the puzzle is to show a graphical view of these differences results based on each category. We cannot drill down per se, but this is a great way to know that the maximum changes seem to be based on “Cell Formats” and then few “Calculated Values” have changed. The INQUIRE option and Spreadsheet Compare 2013 tool is part of Excel 2013. So as you explore using the new version of Excel, there are many such hidden features that are worth exploring. Do let us know if you enjoyed learning a new feature today and I hope you will play around with this feature in your day-today challenges when working with Excel files. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQLAuthority News, T SQL, Technology Tagged: Excel, Personal Technology

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• Low level programming - what's in it for me?

  - by back2dos

  For years I have considered digging into what I consider "low level" languages. For me this means C and assembly. However I had no time for this yet, nor has it EVER been neccessary. Now because I don't see any neccessity arising, I feel like I should either just schedule some point in time when I will study the subject or drop the plan forever. My Position For the past 4 years I have focused on "web technologies", which may change, and I am an application developer, which is unlikely to change. In application development, I think usability is the most important thing. You write applications to be "consumed" by users. The more usable those applications are, the more value you have produced. In order to achieve good usability, I believe the following things are viable Good design: Well-thought-out features accessible through a well-thought-out user interface. Correctness: The best design isn't worth anything, if not implemented correctly. Flexibility: An application A should constantly evolve, so that its users need not switch to a different application B, that has new features, that A could implement. Applications addressing the same problem should not differ in features but in philosophy. Performance: Performance contributes to a good user experience. An application is ideally always responsive and performs its tasks reasonably fast (based on their frequency). The value of performance optimization beyond the point where it is noticeable by the user is questionable. I think low level programming is not going to help me with that, except for performance. But writing a whole app in a low level language for the sake of performance is premature optimization to me. My Question What could low level programming teach me, what other languages wouldn't teach me? Am I missing something, or is it just a skill, that is of very little use for application development? Please understand, that I am not questioning the value of C and assembly. It's just that in my everyday life, I am quite happy that all the intricacies of that world are abstracted away and managed for me (mostly by layers written in C/C++ and assembly themselves). I just don't see any concepts, that could be new to me, only details I would have to stuff my head with. So what's in it for me? My Conclusion Thanks to everyone for their answers. I must say, nobody really surprised me, but at least now I am quite sure I will drop this area of interest until any need for it arises. To my understanding, writing assembly these days for processors as they are in use in today's CPUs is not only unneccesarily complicated, but risks to result in poorer runtime performance than a C counterpart. Optimizing by hand is nearly impossible due to OOE, while you do not get all kinds of optimizations a compiler can do automatically. Also, the code is either portable, because it uses a small subset of available commands, or it is optimized, but then it probably works on one architecture only. Writing C is not nearly as neccessary anymore, as it was in the past. If I were to write an application in C, I would just as much use tested and established libraries and frameworks, that would spare me implementing string copy routines, sorting algorithms and other kind of stuff serving as exercise at university. My own code would execute faster at the cost of type safety. I am neither keen on reeinventing the wheel in the course of normal app development, nor trying to debug by looking at core dumps :D I am currently experimenting with languages and interpreters, so if there is anything I would like to publish, I suppose I'd port a working concept to C, although C++ might just as well do the trick. Again, thanks to everyone for your answers and your insight.

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• C# unit test code questions continue

  - by 5YrsLaterDBA

  more questions after questions in here: http://stackoverflow.com/questions/2714073/c-unit-test-code-questions I found the VS unit test testframe treat private and protected method in the same way but deferent with public method. The following is the generated code for a private method: /// <summary> ///A test for recordLogin ///</summary> [TestMethod()] [DeploymentItem("SystemSoftware.exe")] public void recordLoginTest() { User_Accessor target = new User_Accessor(); // TODO: Initialize to an appropriate value Guid userId = new Guid(); // TODO: Initialize to an appropriate value string action = string.Empty; // TODO: Initialize to an appropriate value Users user = null; // TODO: Initialize to an appropriate value AndeDBEntities db = null; // TODO: Initialize to an appropriate value bool expected = false; // TODO: Initialize to an appropriate value bool actual; actual = target.recordLogin(userId, action, user, db); Assert.AreEqual(expected, actual); Assert.Inconclusive("Verify the correctness of this test method."); } questions: [DeploymentItem("SystemSoftware.exe")] is for private and protected methods, why needs it and what is it for? In my original class/file, if I point to the original method and try to "Find All References". The reference in the unit test class/file will not show up for private and protected methods but it will show up for all public methods. Why is that? Is it right? 3.

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• java time check API

  - by ring bearer

  I am sure this was done 1000 times in 1000 different places. The question is I want to know if there is a better/standard/faster way to check if current "time" is between two time values given in hh:mm:ss format. For example, my big business logic should not run between 18:00:00 and 18:30:00. So here is what I had in mind: public static boolean isCurrentTimeBetween(String starthhmmss, String endhhmmss) throws ParseException{ DateFormat hhmmssFormat = new SimpleDateFormat("yyyyMMddhh:mm:ss"); Date now = new Date(); String yyyMMdd = hhmmssFormat.format(now).substring(0, 8); return(hhmmssFormat.parse(yyyMMdd+starthhmmss).before(now) && hhmmssFormat.parse(yyyMMdd+endhhmmss).after(now)); } Example test case: String doNotRunBetween="18:00:00,18:30:00";//read from props file String[] hhmmss = downTime.split(","); if(isCurrentTimeBetween(hhmmss[0], hhmmss[1])){ System.out.println("NOT OK TO RUN"); }else{ System.out.println("OK TO RUN"); } What I am looking for is code that is better in performance in looks in correctness What I am not looking for third-party libraries Exception handling debate variable naming conventions method modifier issues

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• MYSQL fetch 10 posts, each w/ vote count, sorted by vote count, limited by where clause on posts

  - by nibblebot

  I want to fetch a set of Posts w/ vote count listed, sorted by vote count (e.g.) Post 1 - Post Body blah blah - Votes: 500 Post 2 - Post Body blah blah - Votes: 400 Post 3 - Post Body blah blah - Votes: 300 Post 4 - Post Body blah blah - Votes: 200 I have 2 tables: Posts - columns - id, body, is_hidden Votes - columns - id, post_id, vote_type_id Here is the query I've tried: SELECT p.*, v.yes_count FROM posts p LEFT JOIN (SELECT post_id, vote_type_id, COUNT(1) AS yes_count FROM votes WHERE (vote_type_id = 1) GROUP BY post_id ORDER BY yes_count DESC LIMIT 0, 10) v ON v.post_id = p.id WHERE (p.is_hidden = 0) ORDER BY yes_count DESC LIMIT 0, 10 Correctness: The above query almost works. The subselect is including votes for posts that have is_hidden = 1, so when I left join it to posts, if a hidden post is in the top 10 (ranked by votes), I can end up with records with NULL on the yes_count field. Performance: I have ~50k posts and ~500k votes. On my dev machine, the above query is running in .4sec. I'd like to stay at or below this execution time. Indexes: I have an index on the Votes table that covers the fields: vote_type_id and post_id EXPLAIN id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY p ALL NULL NULL NULL NULL 45985 Using where; Using temporary; Using filesort 1 PRIMARY <derived2> ALL NULL NULL NULL NULL 10 2 DERIVED votes ref VotingPost VotingPost 4 319881 Using where; Using index; Using temporary; Using filesort

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• Query on object id in VQL

  - by Banang

  I'm currently working with the versant object database (using jvi), and have a case where I need to query the database based on an object id. What I'm trying to achieve is something along the lines of Employee employee = new Employee("Mr. Pickles"); session.commit(); FundVQLQuery q = new FundVQLQuery(session, "select * from Employee employee where employee = $1"); q.bind(employee); q.execute(); However, I'm finding out the hard way (I get an EVJ_NOT_A_VALID_KEY_TYPE error thrown at me) that this is infact not the way to do it. Anyone got any experience in working with VQL? Your help is much apreciated! A small clarification: The problem is I'm running some performance tests on the database using the pole position framework, and one of the tests in that framework requires me to fetch an object from the database using either an object reference or a low level object id. Thus, I'm not allowed to reference specific fields in the employee object, but must perform the query on the object in its entirety. So, it's not allowed for me to go "select * from Employee e where e.id = 4", I need it to use the entire object. Accepted answer: Since there is some sort of lunacy magic built into SO that prevents me to mark an accepted answer after a bounty has run out, readers should know that the answer posted by Chris Holmes solves this issue. Readers are encouraged to up-vote his post to further signalize the correctness of his answer to any future readers of this thread.

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• Lazy Sequences that "Look Ahead" for Project Euler Problem 14

  - by ivar

  I'm trying to solve Project Euler Problem 14 in a lazy way. Unfortunately, I may be trying to do the impossible: create a lazy sequence that is both lazy, yet also somehow 'looks ahead' for values it hasn't computed yet. The non-lazy version I wrote to test correctness was: (defn chain-length [num] (loop [len 1 n num] (cond (= n 1) len (odd? n) (recur (inc len) (+ 1 (* 3 n))) true (recur (inc len) (/ n 2))))) Which works, but is really slow. Of course I could memoize that: (def memoized-chain (memoize (fn [n] (cond (= n 1) 1 (odd? n) (+ 1 (memoized-chain (+ 1 (* 3 n)))) true (+ 1 (memoized-chain (/ n 2))))))) However, what I really wanted to do was scratch my itch for understanding the limits of lazy sequences, and write a function like this: (def lazy-chain (letfn [(chain [n] (lazy-seq (cons (if (odd? n) (+ 1 (nth lazy-chain (dec (+ 1 (* 3 n))))) (+ 1 (nth lazy-chain (dec (/ n 2))))) (chain (+ n 1)))))] (chain 1))) Pulling elements from this will cause a stack overflow for n2, which is understandable if you think about why it needs to look 'into the future' at n=3 to know the value of the tenth element in the lazy list because (+ 1 (* 3 n)) = 10. Since lazy lists have much less overhead than memoization, I would like to know if this kind of thing is possible somehow via even more delayed evaluation or queuing?

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• Why does Tex/Latex not speed up in subsequent runs?

  - by Debilski

  I really wonder, why even recent systems of Tex/Latex do not use any caching to speed up later runs. Every time that I fix a single comma*, calling Latex costs me about the same amount of time, because it needs to load and convert every single picture file. (* I know that even changing a tiny comma could affect the whole structure but of course, a well-written cache format could see the impact of that. Also, there might be situations where 100% correctness is not needed as long as it’s fast.) Is there something in the language of Tex which makes this complicated or impossible to accomplish or is it just that in the original implementation of Tex, there was no need for this (because it would have been slow anyway on those large computers)? But then on the other hand, why doesn’t this annoy other people so much that they’ve started a fork which has some sort of caching (or transparent conversion of Tex files to a format which is faster to parse)? Is there anything I can do to speed up subsequent runs of Latex? Except from putting all the stuff into chapterXX.tex files and then commenting them out?

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• In a class with no virtual methods or superclass, is it safe to assume (address of first member vari

  - by Jeremy Friesner

  Hi all, I made a private API that assumes that the address of the first member-object in the class will be the same as the class's this-pointer... that way the member-object can trivially derive a pointer to the object that it is a member of, without having to store a pointer explicitly. Given that I am willing to make sure that the container class won't inherit from any superclass, won't have any virtual methods, and that the member-object that does this trick will be the first member object declared, will that assumption hold valid for any C++ compiler, or do I need to use the offsetof() operator (or similar) to guarantee correctness? To put it another way, the code below does what I expect under g++, but will it work everywhere? class MyContainer { public: MyContainer() {} ~MyContainer() {} // non-virtual dtor private: class MyContained { public: MyContained() {} ~MyContained() {} // Given that the only place Contained objects are declared is m_contained // (below), will this work as expected on any C++ compiler? MyContainer * GetPointerToMyContainer() { return reinterpret_cast<MyContainer *>(this); } }; MyContained m_contained; // MUST BE FIRST MEMBER ITEM DECLARED IN MyContainer int m_foo; // other member items may be declared after m_contained float m_bar; };

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• Why do C# containers and GUI classes use int and not uint for size related members ?

  - by smerlin

  I usually program in C++, but for school i have to do a project in C#. So i went ahead and coded like i was used to in C++, but was surprised when the compiler complained about code like the following: const uint size = 10; ArrayList myarray = new ArrayList(size); //Arg 1: cannot convert from 'uint' to 'int Ok they expect int as argument type, but why ? I would feel much more comfortable with uint as argument type, because uint fits much better in this case. Why do they use int as argument type pretty much everywhere in the .NET library even if though for many cases negative numbers dont make any sense (since no container nor gui element can have a negative size). If the reason that they used int is, that they didnt expect that the average user cares about signedness, why didnt they add overloads for uint additonally ? Is this just MS not caring about sign correctness or are there cases where negative values make some sense/ carry some information (error code ????) for container/gui widget/... sizes ?

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• Thread-safety of read-only memory access

  - by Edmund

  I've implemented the Barnes-Hut gravity algorithm in C as follows: Build a tree of clustered stars. For each star, traverse the tree and apply the gravitational forces from each applicable node. Update the star velocities and positions. Stage 2 is the most expensive stage, and so is implemented in parallel by dividing the set of stars. E.g. with 1000 stars and 2 threads, I have one thread processing the first 500 stars and the second thread processing the second 500. In practice this works: it speeds the computation by about 30% with two threads on a two-core machine, compared to the non-threaded version. Additionally, it yields the same numerical results as the original non-threaded version. My concern is that the two threads are accessing the same resource (namely, the tree) simultaneously. I have not added any synchronisation to the thread workers, so it's likely they will attempt to read from the same location at some point. Although access to the tree is strictly read-only I am not 100% sure it's safe. It has worked when I've tested it but I know this is no guarantee of correctness! Questions Do I need to make a private copy of the tree for each thread? Even if it is safe, are there performance problems of accessing the same memory from multiple threads?

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• When is a method eligible to be inlined by the CLR?

  - by Ani

  I've observed a lot of "stack-introspective" code in applications, which often implicitly rely on their containing methods not being inlined for their correctness. Such methods commonly involve calls to: MethodBase.GetCurrentMethod Assembly.GetCallingAssembly Assembly.GetExecutingAssembly Now, I find the information surrounding these methods to be very confusing. I've heard that the run-time will not inline a method that calls GetCurrentMethod, but I can't find any documentation to that effect. I've seen posts on StackOverflow on several occasions, such as this one, indicating the CLR does not inline cross-assembly calls, but the GetCallingAssembly documentation strongly indicates otherwise. There's also the much-maligned [MethodImpl(MethodImpOptions.NoInlining)], but I am unsure if the CLR considers this to be a "request" or a "command." Note that I am asking about inlining eligibility from the standpoint of contract, not about when current implementations of the JITter decline to consider methods because of implementation difficulties, or about when the JITter finally ends up choosing to inline an eligible method after assessing the trade-offs. I have read this and this, but they seem to be more focused on the last two points (there are passing mentions of MethodImpOptions.NoInlining and "exotic IL instructions", but these seem to be presented as heuristics rather than as obligations). When is the CLR allowed to inline?

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• setting the openCV configuration in an openGL project produce several errors

  - by GolSa

  I have a win32 solution which is set for openGL; it works well; but I want to write a function which use functions of openCV; I set the configuration for openCV for both X86 and X64;;I commented the openCV function and just to test the correctness of configuration, I run it; but when I want to run it on X64 I faced with the error below: Error 1 error C2065: 'GWL_HINSTANCE' : undeclared identifier D:\matrix\matrixProjection\src\ControllerMain.cpp 35 1 matrixProjection Error 2 error C2664: 'CreateDialogParamW' : cannot convert parameter 4 from 'BOOL (__cdecl *)(HWND,UINT,WPARAM,LPARAM)' to 'DLGPROC' D:\matrix\matrixProjection\src\DialogWindow.cpp 47 1 matrixProjection Error 2 points to this line of code: HWND DialogWindow::create() { /*-->this line*/ handle = ::CreateDialogParam(instance, MAKEINTRESOURCE(id), parentHandle, Win::dialogProcedure, (LPARAM)controller); return handle; } but on Debug Win32 configure, it runs; I used openGL32 in my project; is there any probability to be the cause? is there any X64 version for openGL? I know that there is something needed in X64 mode which my solution can not handle it; I googled a lot about it but I did not find any solution; How can I solve that?

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• PHP: Opening/closing tags & performance?

  - by Tom

  Hi, This may be a silly question, but as someone relatively new to PHP, I'm wondering if there are any performance-related issues to frequently opening and closing PHP tags in HTML template code, and if so, what might be best practices in terms of working with php tags? My question is not about the importance/correctness of closing tags, or about which type of code is more readable than another, but rather about how the document gets parsed/executed and what impact it might have on performance. To illustrate, consider the following two extremes: Mixing PHP and HTML tags: <?php echo '<tr> <td>'.$variable1.'</td> <td>'.$variable2.'</td> <td>'.$variable3.'</td> <td>'.$variable4.'</td> <td>'.$variable5.'</td> </tr>' ?> // PHP tag opened once Separating PHP and HTML tags: <tr> <td><?php echo $variable1 ?></td> <td><?php echo $variable2 ?></td> <td><?php echo $variable3 ?></td> <td><?php echo $variable4 ?></td> <td><?php echo $variable5 ?></td> </tr> // PHP tag opened five times Would be interested in hearing some views on this, even if it's just to hear that it makes no difference. Thanks.

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• Safe way for getting/finding a vertex in a graph with custom properties -> good programming practice

  - by Shadow

  Hi, I am writing a Graph-class using boost-graph-library. I use custom vertex and edge properties and a map to store/find the vertices/edges for a given property. I'm satisfied with how it works, so far. However, I have a small problem, where I'm not sure how to solve it "nicely". The class provides a method Vertex getVertex(Vertexproperties v_prop) and a method bool hasVertex(Vertexproperties v_prop) The question now is, would you judge this as good programming practice in C++? My opinion is, that I have first to check if something is available before I can get it. So, before getting a vertex with a desired property, one has to check if hasVertex() would return true for those properties. However, I would like to make getVertex() a bit more robust. ATM it will segfault when one would directly call getVertex() without prior checking if the graph has a corresponding vertex. A first idea was to return a NULL-pointer or a pointer that points past the last stored vertex. For the latter, I haven't found out how to do this. But even with this "robust" version, one would have to check for correctness after getting a vertex or one would also run into a SegFault when dereferencing that vertex-pointer for example. Therefore I am wondering if it is "ok" to let getVertex() SegFault if one does not check for availability beforehand?

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• Runge-Kutta (RK4) integration for game physics

  - by Kai

  Gaffer on Games has a great article about using RK4 integration for better game physics. The implementation is straightforward but the math behind it confuses me. I understand derivatives and integrals on a conceptual level but I haven't manipulated equations in a long time. Here's the brunt of Gaffer's implementation: void integrate(State &state, float t, float dt) { Derivative a = evaluate(state, t, 0.0f, Derivative()); Derivative b = evaluate(state, t+dt*0.5f, dt*0.5f, a); Derivative c = evaluate(state, t+dt*0.5f, dt*0.5f, b); Derivative d = evaluate(state, t+dt, dt, c); const float dxdt = 1.0f/6.0f * (a.dx + 2.0f*(b.dx + c.dx) + d.dx); const float dvdt = 1.0f/6.0f * (a.dv + 2.0f*(b.dv + c.dv) + d.dv) state.x = state.x + dxdt * dt; state.v = state.v + dvdt * dt; } Can anybody explain in simple terms how RK4 works? Specifically, why are we averaging the derivatives at 0.0f, 0.5f, 0.5f, and 1.0f? How is averaging derivatives up to the 4th order different from doing a simple euler integration with a smaller timestep? After reading the accepted answer below, and several other articles, I have a grasp on how RK4 works. To answer my own questions: Can anybody explain in simple terms how RK4 works? RK4 takes advantage of the fact that we can get a much better approximation of a function if we use its higher-order derivatives rather than just the first or second derivative. That's why the Taylor series converges much faster than Euler approximations. (take a look at the animation on the right side of that page) Specifically, why are we averaging the derivatives at 0.0f, 0.5f, 0.5f, and 1.0f? The Runge-Kutta method is an approximation of a function that samples derivatives of several points within a timestep, unlike the Taylor series which only samples derivatives of a single point. After sampling these derivatives we need to know how to weigh each sample to get the closest approximation possible. An easy way to do this is to pick constants that coincide with the Taylor series, which is how the constants of a Runge-Kutta equation are determined. This article made it clearer for me: http://web.mit.edu/10.001/Web/Course%5FNotes/Differential%5FEquations%5FNotes/node5.html. Notice how (15) is the Taylor series expansion while (17) is the Runge-Kutta derivation. How is averaging derivatives up to the 4th order different from doing a simple euler integration with a smaller timestep? Mathematically it converges much faster than doing many Euler approximations. Of course, with enough Euler approximations we can gain equal accuracy to RK4, but the computational power needed doesn't justify using Euler.

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