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• What is better for a student programming in C++ to learn for writing GUI: C# vs QT?

  - by flashnik

  I'm a teacher(instructor) of CS in the university. The course is based on Cormen and Knuth and students program algorithms in C++. But sometimes it is good to show how an algorithm works or just a result of task through GUI. Also in my opinion it's very imporant to be able to write full programs. They will have courses concerning GUI but a three years, later, in fact, before graduatuion. I think that they should be able to write simple GUI applications earlier. So I want to teach them it. How do you think, what is more useful for them to learn: programming GUI with QT or writing GUI in C# and calling unmanaged C++ library? Update. For developing C++ applications students use MS Visual studio, so C# is already installed. But QT AFAIK also can be integrated into VS. I have following pros of C# (some were suggested there in answers): The need to make an additional layer. It's more work, but it forces you explicitly specify contract between GUI and processing data. The border between GUI and algorithms becomes very clear. It's more popular among employers. At least, in Russia where we live. It's rather common to write performance-critical algorithms in C++ and PInvoke them from well-looking C# application/ASP.Net website. Maybe it is not so widespread in the rest of the world but in Russia Windows is very popular, especially in companies and corporations due to some reasons, so most of b2b applications are Windows applications. Rapid development. It's much quicker to code in .Net then in C++ due to many reasons. And the con is that it's a new language with own specific for students. And the mess with invoking calls to library.

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• Rails: update_attribute vs update_attributes

  - by Sam

  Object.update_attribute(:only_one_field, "Some Value") Object.update_attributes(:field1 => "value", :field2 => "value2", :field3 => "value3") Both of these will update an object without having to explicitly tell AR to update. Rails API says: for update_attribute Updates a single attribute and saves the record without going through the normal validation procedure. This is especially useful for boolean flags on existing records. The regular update_attribute method in Base is replaced with this when the validations module is mixed in, which it is by default. for update_attributes Updates all the attributes from the passed-in Hash and saves the record. If the object is invalid, the saving will fail and false will be returned. So if I don't want to have the object validated I should use update_attribute. What if I have this update on a before_save, will it stackoverflow? My question is does update_attribute also bypass the before save or just the validation. Also, what is the correct syntax to pass a hash to update_attributes... check out my example at the top.

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• DCI: How to implement Context with Dependency Injection?

  - by ciscoheat

  Most examples of a DCI Context are implemented as a Command pattern. When using Dependency Injection though, it's useful to have the dependencies injected in the constructor and send the parameters into the executing method. Compare the Command pattern class: public class SomeContext { private readonly SomeRole _someRole; private readonly IRepository<User> _userRepository; // Everything goes into the constructor for a true encapsuled command. public SomeContext(SomeRole someRole, IRepository<User> userRepository) { _someRole = someRole; _userRepository = userRepository; } public void Execute() { _someRole.DoStuff(_userRepository); } } With the Dependency injected class: public class SomeContext { private readonly IRepository<User> _userRepository; // Only what can be injected using the DI provider. public SomeContext(IRepository<User> userRepository) { _userRepository = userRepository; } // Parameters from the executing method public void Execute(SomeRole someRole) { someRole.DoStuff(_userRepository); } } The last one seems a bit nicer, but I've never seen it implemented like this so I'm curious if there are any things to consider.

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• Do I need a spatial index in my database?

  - by Sanoj

  I am designing an application that needs to save geometric shapes in a database. I haven't choosen the database management system yet. In my application, all database queries will have an bounding box as input, and as output I want all shapes within that database. I know that databases with a spatial index is used for this kind of application. But in my application there will not be any queries of type "give me objects nearby x/y" or other more complex queries that are useful in a GIS application. I am planning of having a database without a spatial index and have queries looking like: SELECT * FROM shapes WHERE x < max_x AND x > min_x AND y < max_y AND y > min_y And have an index on the columns x (double) and y (double). As long I can see, I don't really need a database with an spatial index, howsoever my application is close to that kind of applications. And even if I would like to have nearby queries, then I could create a big enough bounding box around that point. Or will this lead to poor performance? Do I really need a spatial database? And when is a spatial index needed?

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• Is "tip-of-the-day" good?

  - by Jonta

  Many programs (often large ones, like MS Office, The GIMP, Maxthon) have a feature called "tip-of-the-day". It explains a small part of the program, like this one in Maxthon: "You can hide/show the main menu bar by pressing Ctrl+F11" You can usually browse through them by clicking next. And other options provided are "Previous", "Close", "Do not show at startup". I think I like the way Maxthon used to handle this; in the browser's statusbar (down at the bottom usually, together with "Done", the progress-bar etc), there would sometimes be a small hint or tip on what else you could do with it. As Joel Spolsky wrote in his article-series "User Interface Design for Programmers", people don't like reading manuals. But we still want them to use the program, and the features they could benefit from, don't we? Therefore, I think it is useful to have such a feature, without the annoyance of the pop-up on startup. What do you think? Pop-up? Maxthonstyle? No way?

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• Confused about std::runtime_error vs. std::logic_error

  - by David Gladfelter

  I recently saw that the boost program_options library throws a logic_error if the command-line input was un-parsable. That challenged my assumptions about logic_error vs. runtime_error. I assumed that logic errors (logic_error and its derived classes) were problems that resulted from internal failures to adhere to program invariants, often in the form of illegal arguments to internal API's. In that sense they are largely equivalent to ASSERT's, but meant to be used in released code (unlike ASSERT's which are not usually compiled into released code.) They are useful in situations where it is infeasible to integrate separate software components in debug/test builds or the consequences of a failure are such that it is important to give runtime feedback about the invalid invariant condition to the user. Similarly, I thought that runtime_errors resulted exclusively from runtime conditions outside of the control of the programmer: I/O errors, invalid user input, etc. However, program_options is obviously heavily (primarily?) used as a means of parsing end-user input, so under my mental model it certainly should throw a runtime_error in the case of bad input. Where am I going wrong? Do you agree with the boost model of exception typing?

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• How to get readable classname and title from HWND handle? in WinApi c++

  - by Marko29

  I am using the following enumchild proc to get hwnd of each window, the problem is that i am unable to somehow detect any info from each hwnd so i can do what i want with the ones that are detected as the ones i need. For example, how could i get window class name and the title of each window in the enum bellow? I tried something like.. BOOL CALLBACK EnumChildProc(HWND hwnd, LPARAM lParam) { TCHAR className[MAX_PATH]; GetClassName(hwnd, cName, _countof(cName)); cout << cName; return TRUE; } It just returns the hexadec handle info and every single time it is same, shouldnt the GetClassName func change the cName into new handle each time? Also GetClassName function returns number of chars written to cName, i dont really see how this is useful to me? I need to get my cName in some readable format so i can do something like if(cName == TEXT("classnameiamlookingfor" && hwndtitle = TEXT("thetitlethatinterestsme") DOSOMETHINGWITHIT(); But all i get here is hexadec mess.

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• Pushing or serving real-time data to an excel spreadsheet

  - by evan_irl

  I am running some test automation on a networked computer resource (remote). The remote computer running the test automation generates some output, which I can customize however I wish - probably a text or excel file. I would like to create an excel spreadsheet which, from my local machine, monitors this output and provides real-time analytics. Later I would make the networked computer visible to more people, and they can use the same spreadsheet to monitor this output. My problem is that this networked computer is located on the other side of the earth, and so using any kind of polling in excel VBA to PULL the data from the networked computer results in a very long wait with the pinwheel spinning, making the sheet clumsy and less useful. The same thing happens when I use excel's built in function for linking to "external resources" Is there any way to PUSH data to the excel spreadsheet from the networked computer? Something that is easy to set up would be ideal, the latency does not have to be low, so long as there is no awkward "busy wait" while the sheet updates. If that is not possible, is there any way of using PULL from the excel sheet that avoids the same busy wait?

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• Question about array subscripting in C#

  - by Michael J

  Back in the old days of C, one could use array subscripting to address storage in very useful ways. For example, one could declare an array as such. This array represents an EEPROM image with 8 bit words. BYTE eepromImage[1024] = { ... }; And later refer to that array as if it were really multi-dimensional storage BYTE mpuImage[2][512] = eepromImage; I'm sure I have the syntax wrong, but I hope you get the idea. Anyway, this projected a two dimension image of what is really single dimensional storage. The two dimensional projection represents the EEPROM image when loaded into the memory of an MPU with 16 bit words. In C one could reference the storage multi-dimensionaly and change values and the changed values would show up in the real (single dimension) storage almost as if by magic. Is it possible to do this same thing using C#? Our current solution uses multiple arrays and event handlers to keep things synchronized. This kind of works but it is additional complexity that we would like to avoid if there is a better way.

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• Plugin architecture in C using libdl

  - by LukeN

  I've been toying around, writing a small IRC framework in C that I'm now going to expand with some core functionality - but beyond that, I'd like it to be extensible with plugins! Up until now, whenever I wrote something IRC related (and I wrote a lot, in about 6 different languages now... I'm on fire!) and actually went ahead to implement a plugin architecture, it was inside an interpreted language that had facilities for doing (read: abusing) so, like jamming a whole script file trough eval in Ruby (bad!). Now I want to abuse something in C! Basically there's three things I could do define a simple script language inside of my program use an existing one, embedding an interpreter use libdl to load *.so modules on runtime I'm fond of the third one and raather avoid the other two options if possible. Maybe I'm a masochist of some sort, but I think it could be both fun and useful for learning purposes. Logically thinking, the obvious "pain-chain" would be (lowest to highest) 2 - 1 - 3, for the simple reason that libdl is dealing with raw code that can (and will) explode in my face more often than not. So this question goes out to you, fellow users of stackoverflow, do you think libdl is up to this task, or even a realistic thought?

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• Create a console from within a non-console .NET application.

  - by pauldoo

  How can I open a console window from within a non-console .NET application (so I have a place for System.Console.Out and friends when debugging)? In C++ this can be done using various Win32 APIs: /* EnsureConsoleExists() will create a console window and attach stdout (and friends) to it. Can be useful when debugging. */ FILE* const CreateConsoleStream(const DWORD stdHandle, const char* const mode) { const HANDLE outputHandle = ::GetStdHandle(stdHandle); assert(outputHandle != 0); const int outputFileDescriptor = _open_osfhandle(reinterpret_cast<intptr_t>(outputHandle), _O_TEXT); assert(outputFileDescriptor != -1); FILE* const outputStream = _fdopen(outputFileDescriptor, mode); assert(outputStream != 0); return outputStream; } void EnsureConsoleExists() { const bool haveCreatedConsole = (::AllocConsole() != 0); if (haveCreatedConsole) { /* If we didn't manage to create the console then chances are that stdout is already going to a console window. */ *stderr = *CreateConsoleStream(STD_ERROR_HANDLE, "w"); *stdout = *CreateConsoleStream(STD_OUTPUT_HANDLE, "w"); *stdin = *CreateConsoleStream(STD_INPUT_HANDLE, "r"); std::ios::sync_with_stdio(false); const HANDLE consoleHandle = ::GetStdHandle(STD_OUTPUT_HANDLE); assert(consoleHandle != NULL && consoleHandle != INVALID_HANDLE_VALUE); CONSOLE_SCREEN_BUFFER_INFO info; BOOL result = ::GetConsoleScreenBufferInfo(consoleHandle, &info); assert(result != 0); COORD size; size.X = info.dwSize.X; size.Y = 30000; result = ::SetConsoleScreenBufferSize(consoleHandle, size); assert(result != 0); } }

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• Can Visual Studio (should it be able to) compute a diff between any two changesets associated with a

  - by Hamish Grubijan

  Here is my use case: I start on a project XYZ, for which I create a work item, and I make frequent check-ins, easily 10-20 in total. ALL of the code changes will be code-read and code-reviewed. The change sets are not consecutive - other people check-in in-between my changes, although they are very unlikely to touch the exact same files. So ... at the en of the project I am interested in a "total diff" - as if there was a single check-in by me to complete the entire project. In theory this is computable. From the list of change sets associated with the work item, you get the list of all files that were affected. Then, the algorithm can aggregate individual diffs over each file and combine them into one. It is possible that a pure total diff is uncomputable due to the fact that someone else renamed files, or changed stuff around very closely, or in the same functions as me. I that case ... I suppose a total diff can include those changes by non-me as well, and warn me about the fact. I would find this very useful, but I do not know how to do t in practice. Can Visual Studio 2008/2010 (and/or TFS server) do it? Are there other source control systems capable of doing this? Thanks.

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• iPhone application purchase verification -- possible?

  - by Sedate Alien

  The iPhone 3.0 SDK's StoreKit.framework provides support for in-app purchases to give the user additional content, functionality and so on. It is possible for an app to send the transactionReceipt property of SKPaymentTransaction objects to the developer's server for verification of successful purchasing before granting service. Is there any analogous SDK to verify the initial application purchase itself? A developer that wishes for their server to only provide services to genuine applications (i.e. not pirated) without using IAP could do so by verifying the application in this manner, e.g. ensure that only users with the correct transactionReceipt are catered for. I understand that this approach would still be vulnerable to replay attacks; a dedicated group of pirates could share a valid transactionReceipt. However, my server provides a consumable service to users, i.e. once they've connected and done the work, it needn't work a second time so replay attacks are nullified. The service that my app provides is relatively niche. I could distribute it on the App Store as a free application that requires at least one IAP to do anything useful, but I am lead to believe that this would be a very unpopular move among users as it would be considered misleading. If I distribute it as a paid app, I do not know how to ensure that only genuine apps can access the webservice. This is important as every invocation of the webservice costs me money! What are my options?

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• Making a Delete and Reply button in Jquery

  - by Branko Ostojic

  this is my second post on the website. Of all other sites i tried, this one gave the most accurate and useful information! I'm in a bit of a trouble with buttons, i have a task to make an inbox and to add a "reply" and "delete" button into every instance of the message. I was indeed wandering if there is a better way to do that than forcing the HTML code into the script, because every message is dynamically generated. Any help and/or suggestions would be very appreciated!(The objects are called from a JSON file). $(document).ready(function(){ $.getJSON('public/js/data.json', function(json){ $.each(json.data, function(i, data){ var output = ''; if(data.from.id != '234' && data.from.name != 'Alan Ford'){ $("#inbox").append( output += '<div class="post">'+ '<div class="h1">'+data.from.name+' - '+data.subject+'</div>'+ //this gives the name of the person who sent the message and the subject '<div class="content">'+data.message_formatted+'</div>'+ //The content of the message //buttons should be squeezed left of the date //this gives the date of the message sent '<div class="time">'+data.date_sent_formatted.formatted+'</div>'+ '</div>' ); }}); }); }); var date_sent=convertToDateTime(); function delete_message(id){ console.log('Delete message with id: '+id); } function reply_message(id, sender){ console.log('Message id: '+id); console.log('Reply to: '+sender); } The complete code in the JSFiddle . Just copy/pasted!

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• How to implement a multi-threaded asynchronous operation?

  - by drowneath

  Here's how my current approach looks like: // Somewhere in a UI class // Called when a button called "Start" clicked MyWindow::OnStartClicked(Event &sender) { _thread = new boost::thread(boost::bind(&MyWindow::WorkToDo, this)); } MyWindow::WorkToDo() { for(int i = 1; i < 10000000; i++) { int percentage = (int)((float)i / 100000000.f); _progressBar->SetValue(percentage); _statusText->SetText("Working... %d%%", percentage); printf("Pretend to do something useful...\n"); } } // Called on every frame MyWindow::OnUpdate() { if(_thread != 0 && _thread->timed_join(boost::posix_time::seconds(0)) { _progressBar->SetValue(100); _statusText->SetText("Completed!"); delete _thread; _thread = 0; } } But I'm afraid this is far from safe since I keep getting unhandled exception at the end of the program execution. I basically want to separate a heavy task into another thread without blocking the GUI part.

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• Why can't we just use a hash of passphrase as the encryption key (and IV) with symmetric encryption algorithms?

  - by TX_

  Inspired by my previous question, now I have a very interesting idea: Do you really ever need to use Rfc2898DeriveBytes or similar classes to "securely derive" the encryption key and initialization vector from the passphrase string, or will just a simple hash of that string work equally well as a key/IV, when encrypting the data with symmetric algorithm (e.g. AES, DES, etc.)? I see tons of AES encryption code snippets, where Rfc2898DeriveBytes class is used to derive the encryption key and initialization vector (IV) from the password string. It is assumed that one should use a random salt and a shitload of iterations to derive secure enough key/IV for the encryption. While deriving bytes from password string using this method is quite useful in some scenarios, I think that's not applicable when encrypting data with symmetric algorithms! Here is why: using salt makes sense when there is a possibility to build precalculated rainbow tables, and when attacker gets his hands on hash he looks up the original password as a result. But... with symmetric data encryption, I think this is not required, as the hash of password string, or the encryption key, is never stored anywhere. So, if we just get the SHA1 hash of password, and use it as the encryption key/IV, isn't that going to be equally secure? What is the purpose of using Rfc2898DeriveBytes class to generate key/IV from password string (which is a very very performance-intensive operation), when we could just use a SHA1 (or any other) hash of that password? Hash would result in random bit distribution in a key (as opposed to using string bytes directly). And attacker would have to brute-force the whole range of key (e.g. if key length is 256bit he would have to try 2^256 combinations) anyway. So either I'm wrong in a dangerous way, or all those samples of AES encryption (including many upvoted answers here at SO), etc. that use Rfc2898DeriveBytes method to generate encryption key and IV are just wrong.

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• Smarter println that shows the depth in the stack

  - by Hectoret

  I am using System.out.println in my code to track the execution of a program and get some useful output. This creates results like this in the console: Main function. Program starts. Method getArea. Getting values Method getSide. Side is 6 Method getArea. First value is 6 Method getSide. Side is 8 Method getArea. Second value is 8 Method getArea. Area is 48 Main function. The final area is 48 I would like to create tha method, which adds a space in front of the output every time the code goes deeper in the method call stack. For example, the same code but instead of using System.out.println, now with Misc.smartPrintln: Main function. Program starts. Method getArea. Getting values Method getSide. Side is 6 Method getArea. First value is 6 Method getSide. Side is 8 Method getArea. Second value is 8 Method getArea. Area is 48 Main function. The final area is 48 The method would have this definition: public static void smartPrintln(String string); I don't know how to implement this functionality. Any ideas how to solve this? And, could the use of a logger offer this functionality?

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• What are the possible tags inside the "global" tag in Magento "config.xml" file?

  - by Knowledge Craving

  Can someone professional experienced Magento developer tell me how to accomplish the following in Magento? I want to know what are the possible tags that can fit in the "global" tag of the "config.xml" page of every module's etc folder? I have tried searching for this answer at many places in Internet but in vain. Please provide the full details along with it for Magento version = 1.4.0.0, because I want at least the users accessing this website find it useful enough, instead of scratching their heads. I really want a detailed explanation, because every newbie like me gets totally confused at this point. From what I know till now, is that in this page, you can set routers, rewrites, cron jobs, admin html, front-end html and many more. But without any strong concepts, none can go ahead with the belief that his code is 100% correct w.r.t. the Magento MVC architecture. So please I want that strong fundamental concept, getting underlined here, with a detailed explanation about it, so that no one gets into this pitfall ever again. Many many thanks to those who can answer only upon knowing the total concept clearly.

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• Where to start with the development of first database driven Web App (long question)?

  - by Ryan

  Hi all, I've decided to develop a database driven web app, but I'm not sure where to start. The end goal of the project is three-fold: 1) to learn new technologies and practices, 2) deliver an unsolicited demo to management that would show how information that the company stores as office documents spread across a cumbersome network folder structure can be consolidated and made easier to access and maintain and 3) show my co-workers how Test Drive Development and prototyping via class diagrams can be very useful and reduces future maintenance headaches. I think this ends up being a basic CMS to which I have generated a set of features, see below. 1) Create a database to store the site structure (organized as a tree with a 'project group'-project structure). 2) Pull the site structure from the database and display as a tree using basic front end technologies. 3) Add administrator privileges/tools for modifying the site structure. 4) Auto create required sub pages* when an admin adds a new project. 4.1) There will be several sub pages under each project and the content for each sub page is different. 5) add user privileges for assigning read and write privileges to sub pages. What I would like to do is use Test Driven Development and class diagramming as part of my process for developing this project. My problem; I'm not sure where to start. I have read on Unit Testing and UML, but never used them in practice. Also, having never worked with databases before, how to I incorporate these items into the models and test units? Thank you all in advance for your expertise.

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• Adding functions to Java class libraries

  - by Eric

  I'm using a Java class library that is in many ways incomplete: there are many classes that I feel ought to have additional member functions built in. However, I am unsure of the best practice of adding these member functions. Lets call the insufficient base class A. class A { public A(/*long arbitrary arguments*/) { //... } public A(/*long even more arbitrary arguments*/) { //... } public int func() { return 1; } } Ideally, I would like to add a function to A. However, I can't do that. My choice is between: class B extends A { //Implement ALL of A's constructors here public int reallyUsefulFunction() { return func()+1; } } and class AddedFuncs { public int reallyUsefulFunction(A a) { return a.func()+1; } } The way I see it, they both have advantages and disadvantages. The first choice gives a cleaner syntax than the second, and is more logical, but has problems: Let's say I have a third class, C, within the class library. class C { public A func() { return new A(/*...*/); } } As I see it, there is no easy way of doing this: C c; int useful = c.func().reallyUsefulFunction(); as the type returned by C.func() is an A, not a B, and you can't down-cast. So what is the best way of adding a member function to a read-only library class?

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• performance issue: difference between select s.* vs select *

  - by kamil

  Recently I had some problem in performance of my query. The thing is described here: poor Hibernate select performance comparing to running directly - how debug? After long time of struggling, I've finally discovered that the query with select prefix like: select sth.* from Something as sth... Is 300x times slower then query started this way: select * from Something as sth.. Could somebody help me, and asnwer why is that so? Some external documents on this would be really useful. The table used for testing was: SALES_UNIT table contains some basic info abot sales unit node such as name and etc. The only association is to table SALES_UNIT_TYPE, as ManyToOne. The primary key is ID and field VALID_FROM_DTTM which is date. SALES_UNIT_RELATION contains relation PARENT-CHILD between sales unit nodes. Consists of SALES_UNIT_PARENT_ID, SALES_UNIT_CHILD_ID and VALID_TO_DTTM/VALID_FROM_DTTM. No association with any tables. The PK here is ..PARENT_ID, ..CHILD_ID and VALID_FROM_DTTM The actual query I've done was: select s.* from sales_unit s left join sales_unit_relation r on (s.sales_unit_id = r.sales_unit_child_id) where r.sales_unit_child_id is null select * from sales_unit s left join sales_unit_relation r on (s.sales_unit_id = r.sales_unit_child_id) where r.sales_unit_child_id is null Same query, both uses left join and only difference is with select.

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• Why is joining two vectors simply not working?

  - by Jim

  I have two vectors of MyObj structs. MyObj is defined as follows: struct MyObj { float x, y; unsigned int data[8]; unsigned int tmp[1]; MyObj(const MyObj &m) { x = m.x; y = m.y; tmp[0] = 0; for (int i = 0; i < 8; ++i) { data[i] = m.data[i]; } } }; I then have two vectors... vector<MyObj> v1; vector<MyObj> v2; // both get data eventually. v1.insert(v1.end(), v2.begin(), v2.end()); v2 has 3535004 elements in my experiment. v1 is similarly sized. I've also tried building a new vector and just using .push_back to build it from both vectors. Essentially, when I try to merge the two vectors I just get an error from visual studio saying "Debug error! R6010, abort() has been called". Very non-useful... So my question is: what could be causing this error, and how can I solve it? Thank you

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• Looking for a book which teaches how to write applications (as opposed to writng code)

  - by rumtscho

  I am not a developer. I have coded for fun and for university projects in several languages, and during an internship, I have written code which is still in use by a department of Fortune Global 500 company. I also have extensive theoretical knowledge of software engineering - process models, architecture, project management, UI construction using Lauesen's virtual windows... you get the picture. But I am not involved with software development in my job. I recently decided to start coding for fun again, and now I have some free days to do it. But this time, I want to do it right. I want to write a real, useful application, install it on my devices and use it myself. Also I want to publish it for others to use, should they want to do so. I am vaguely aware that there is more to writing an application than to writing code. There is stuff like version control software, decision for the right IDE, having a suite of unit tests, producing an installation package - and probably lots of other things I never thought of but which must be taken care of in a proper application, as opposed to a bunch of classes I am running from my IDE. All this is stuff I should know before I start, but I have not learned it. Coding books touch on some of the subjects like IDE choice, but don't go into detail, and are not exhaustive. Theoretical software engineering textbooks are even less helpful. So is there a book which teaches exactly that? I know that I can find information on each of these topics on the Internet, but I'd rather have a systematic book exhaustively listing all the things I should take care of if I want to create a good application, and offering the currently accepted solutions for them. In the best case, it will be language- and platform independent, but if you know of a good book focusing on a specific platform, I would like to know about it too. I know I want a lot, but given how important such knowledge is and how many people need it, surely somebody must have written such a book?

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• C#: How to implement a smart cache

  - by Svish

  I have some places where implementing some sort of cache might be useful. For example in cases of doing resource lookups based on custom strings, finding names of properties using reflection, or to have only one PropertyChangedEventArgs per property name. A simple example of the last one: public static class Cache { private static Dictionary<string, PropertyChangedEventArgs> cache; static Cache() { cache = new Dictionary<string, PropertyChangedEventArgs>(); } public static PropertyChangedEventArgs GetPropertyChangedEventArgsa(string propertyName) { if (cache.ContainsKey(propertyName)) return cache[propertyName]; return cache[propertyName] = new PropertyChangedEventArgs(propertyName); } } But, will this work well? For example if we had a whole load of different propertyNames, that would mean we would end up with a huge cache sitting there never being garbage collected or anything. I'm imagining if what is cached are larger values and if the application is a long-running one, this might end up as kind of a problem... or what do you think? How should a good cache be implemented? Is this one good enough for most purposes? Any examples of some nice cache implementations that are not too hard to understand or way too complex to implement?

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• How costly performance-wise are these actions in iPhone objective-C?

  - by Alex Gosselin

  This is really a few questions in one, I'm wondering what the performance cost is for these things, as I haven't really been following a best practice of any sort for these. The answers may also be useful to other readers, if somebody knows these. (1) If I need the core data managed object context, is it bad to use #import "myAppDelegate.h" //farther down in the code: NSManagedObjectContext *context = [(myAppDelegate.h*)[[UIApplication sharedApplication] delegate] managedObjectContext]; as opposed to leaving the warning you get if you don't cast the delegate? (2) What is the cheapest way to hard-code a string? I have been using return @"myString"; on occasion in some functions where I need to pass it to a variety of places, is it better to do it this way: static NSString *str = @"myString"; return str; (3) How costly is it to subclass an object i wrote vs. making a new one, in general? (4) When I am using core data and navigating through a hierarchy of some sort, is it necessary to turn things back into faults somehow after I read some info from them? or is this done automatically? Thanks for any help.

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