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  • Object inheritance and method parameters/return types - Please check my logic

    - by user2368481
    I'm preparing for a test and doing practice questions, this one in particular I am unsure I did correctly: We are given a very simple UML diagram to demonstrate inheritance: I hope this is clear, it shows that W inherits from V and so on: |-----Y V <|----- W<|-----| |-----X<|----Z and this code: public X method1(){....} method2(new Y()); method2(method1()); method2(method3()); The questions and my answers: Q: What types of objects could method1 actually return? A: X and Z, since the method definition includes X as the return type and since Z is a kind of X is would be OK to return either. Q: What could the parameter type of method2 be? A: Since method2 in the code accepts Y, X and Z (as the return from method1), the parameter type must be either V or W, as Y,X and Z inherit from both of these. Q: What could return type of method3 be? A: Return type of method3 must be V or W as this would be consistent with answer 2.

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  • How are generics implemented?

    - by greenoldman
    This is the question from compiler internals perspective. I am interested in generics, not templates (C++), so I marked the question with C#. Not Java, because AFAIK the generics in both languages differ in implementations. When I look at languages w/o generics it is pretty straightforward, you can validate the class definition, add it to hierarchy and that's it. But what to do with generic class, and more importantly how handle references to it? How to make sure that static fields are singular per instantiations (i.e. each time generic parameters are resolved). Let's say I see a call: var x = new Foo<Bar>(); Do I add new Foo_Bar class to hierarchy? Update: So far I found only 2 relevant posts, however even they don't go into much details in sense "how to do it by yourself": http://www.jprl.com/Blog/archive/development/2007/Aug-31.html http://www.artima.com/intv/generics2.html

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  • Does your organization still use the term "screens" to describe a user interface?

    - by bit-twiddler
    I have been in the field long enough to remember when the term "screen" entered our lexicon. As difficult as it is to believe, the early systems on which I worked had no user interface (UI), that is, unless one counts a keypunch machine and job listings as a user interface. These systems ran as "card image" production jobs back in a day when being a computer operator required a reasonably deep understanding of how computers worked. Flashing forward to today: I cringe every time I hear a systems practitioner use the term "screen." The metaphor no longer fits the medium. The term somewhat fit back when the user dialog consumed 100% of available monitor real estate; however, the term lost its relevance the moment we moved to windowed environments. With the above said, does your organization still use the term "screens" to describe an application's UI? Has anyone successfully purged the term from an organization? For those who do not use the term to describe UI dialog elements, what term do you use in place of “screen.”

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  • Does Agile force developers to work more?

    - by Shooshpanchick
    Looking at common Agile practices it seems to me that they (intentionally or unintentionally?) force developer to spend more time actually working as opposed to reading blogs/articles, chatting, coffee breaks and just plain procrastinating. In particular: 1) Pair programming - the biggest work-forcer, just because it is inconvenient to do all that procrastination when there are two of you sitting together. 2) Short stories - when you have a HUGE chunk of work that must be done in e.g. a month, it is pretty common to slack off in the first three weeks and switch to OMG DEADLINE mode for the last one. And with the little chunks (that must be done in a day or less) it is exact opposite - you feel that time is tight, there is no space for maneuvering, and you will be held accountable for the task pretty soon, so you start working immediately. 3) Team communication and cohesion - when you underperform in a slow, distanced and silent environment it may feel ok, but when at the end of the day at Scrum meeting everyone boasts what they have accomplished and you have nothing to say you may actually feel ashamed. 4) Testing and feedback - again, it prevents you from keeping tasks "99% ready" (when it's actually around 20%) until the deadline suddenly happens. Do you feel that under Agile you work more than under "conventional" methodologies? Is this pressure compensated by the more comfortable environment and by the feeling of actually getting right things done quickly?

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  • Spring + JSR 303 Validation group is ignored [closed]

    - by nsideras
    we have a simple bean with JSR annotations public class CustomerDTO { private static final long serialVersionUID = 1L; private Integer id; @NotEmpty(message = "{customer.firstname.empty}") private String firstName; @NotEmpty(message = "{customer.lastname.empty}") private String lastName; @NotEmpty(groups={PasswordChange.class}, message="{password.empty}") private String password; @NotEmpty(groups={PasswordChange.class}, message="{confirmation.password.empty}") private String password2; } and we have a Spring Controller @RequestMapping(value="/changePassword", method = RequestMethod.POST) public String changePassword(@Validated({ PasswordChange.class }) @ModelAttribute("customerdto") CustomerDTO customerDTO, BindingResult result, Locale locale) { logger.debug("Change Password was submitted with information: " + customerDTO.toString()); try { passwordStrengthPolicy.checkPasswordStrength(locale, customerDTO.getPassword()); if (result.hasErrors()) { return "changePassword"; } logger.debug("Calling customer service changePassword: " + customerDTO); customerOnlineNewService.changePassword(customerDTO); } catch (PasswordNotChangedException e) { logger.error("Could not change password PasswordNotChangedException: " + customerDTO.toString()); return "changePassword"; } catch (PasswordNotSecureException e) { return "changePassword"; } return createRedirectViewPath("changePassword"); } Our problem is that when changePassword is invoked the validator ignores the group(PasswordChange.class) and validates only firstName and lastName which are not in the group. Any idea? Thank you very much for your time.

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  • UI Controls Copyright

    - by user3692481
    I'm developing a cross-platform computer software. It will run on Windows and Mac OS X. For user experience reasons, I want it to have the same graphic on both platforms. I really like the Mac OS UI controls and I'd love to see them on the Windows version too. My question is: is it legal to "copy" UI components? I'm not going to copy icons or reproduce an existing Apple software. I would only "copy" some standard UI components such as Buttons, Progressbars, TreeView, ListView etc. You can see them here: http://i.stack.imgur.com/9YzYQ.png http://i.stack.imgur.com/MWR6B.jpg IMHO, they should not be copyrighted for two reasons: They are implicitly used by any Mac OS software There are a lot of Apps (for Windows and even Web-Apps) that are "inspired by" the Mac graphic. Am I right?

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  • Earmarks of a Professional PHP Programmer

    - by Scotty C.
    I'm a 19 year old student who really REALLY enjoys programming, and I'm hoping to glean from your years of experience here. At present, I'm studying PHP every chance I get, and have been for about 3 years, although I've never taken any formal classes. I'd love to some day be a programmer full time, and make a good career of it. My question to you is this: What do you consider to be the earmarks or traits of a professional programmer? Mainly in the field of PHP, but other, more generalized qualifications are also more than welcome, as I think PHP is more of a hobbyist language and may not be the language of choice in the eyes of potential employers. Please correct me if I'm wrong. Above all, I don't want to wast time on something that isn't worth while. I'm currently feeling pretty confident in my knowledge of PHP as a language, and I know that I could build just about anything I need and have it "work", but I feel sorely lacking in design concepts and code structure. I can even write object oriented code, but in my personal opinion, that isn't worth a hill of beans if it isn't organized well. For this reason, I bought Matt Zandstra's book "PHP Objects, Patterns, and Practice" and have been reading that a little every day. Anyway, I'm starting to digress a little here, so back to the original question. What advice would you give to an aspiring programmer who wants to make an impact in this field? Also, on a side note, I've been working on a project with a friend of mine that would give a fairly good idea of where I'm at coding wise. I'm gonna give a link, I don't want anyone to feel as though I'm pushing or spamming here, so don't click it if you don't want to. But if you are interested on giving some feedback there as well, you can see the code on github. I'm known as The Craw there. https://github.com/PureChat/PureChat--Beta-/tree/

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  • Unit-testing code that relies on untestable 3rd party code

    - by DudeOnRock
    Sometimes, especially when working with third party code, I write unit-test specific code in my production code. This happens when third party code uses singletons, relies on constants, accesses the file-system/a resource I don't want to access in a test situation, or overuses inheritance. The form my unit-test specific code takes is usually the following: if (accessing or importing a certain resource fails) I assume this is a test case and load a mock object Is this poor form, and if it is, what is normally done when writing tests for code that uses untestable third party code?

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  • What's the best/most efficent way to create a semi-intelligent AI for a tic tac toe game?

    - by Link
    basically I am attempting to make a a efficient/smallish C game of Tic-Tac-Toe. I have implemented everything other then the AI for the computer so far. my squares are basically structs in an array with an assigned value based on the square. For example s[1].value = 1; therefore it's a x, and then a value of 3 would be a o. My question is whats the best way to create a semi-decent game playing AI for my tic-tac-toe game? I don't really want to use minimax, since It's not what I need. So how do I avoid a a lot of if statments and make it more efficient. Here is the rest of my code: #include <stdio.h> #include <stdlib.h> #include <string.h> #include <time.h> struct state{ // defined int state; // 0 is tie, 1 is user loss, 2 is user win, 3 is ongoing game int moves; }; struct square{ // one square of the board int value; // 1 is x, 3 is o char sign; // no space used }; struct square s[9]; //set up the struct struct state gamestate = {0,0}; //nothing void setUpGame(){ // setup the game int i = 0; for(i = 0; i < 9; i++){ s[i].value = 0; s[i].sign = ' '; } gamestate.moves=0; printf("\nHi user! You're \"x\"! I'm \"o\"! Good Luck :)\n"); } void displayBoard(){// displays the game board printf("\n %c | %c | %c\n", s[6].sign, s[7].sign, s[8].sign); printf("-----------\n"); printf(" %c | %c | %c\n", s[3].sign, s[4].sign, s[5].sign); printf("-----------\n"); printf(" %c | %c | %c\n\n", s[0].sign, s[1].sign, s[2].sign); } void getHumanMove(){ // get move from human int i; while(1){ printf(">>:"); char line[255]; // input the move to play fgets(line, sizeof(line), stdin); while(sscanf(line, "%d", &i) != 1) { //1 match of defined specifier on input line printf("Sorry, that's not a valid move!\n"); fgets(line, sizeof(line), stdin); } if(s[i-1].value != 0){printf("Sorry, That moves already been taken!\n\n");continue;} break; } s[i-1].value = 1; s[i-1].sign = 'x'; gamestate.moves++; } int sum(int x, int y, int z){return(x*y*z);} void getCompMove(){ // get the move from the computer } void checkWinner(){ // check the winner int i; for(i = 6; i < 9; i++){ // check cols if((sum(s[i].value,s[i-3].value,s[i-6].value)) == 8){printf("The Winner is o!\n");gamestate.state=1;} if((sum(s[i].value,s[i-3].value,s[i-6].value)) == 1){printf("The Winner is x!\n");gamestate.state=2;} } for(i = 0; i < 7; i+=3){ // check rows if((sum(s[i].value,s[i+1].value,s[i+2].value)) == 8){printf("The Winner is o!\n");gamestate.state=1;} if((sum(s[i].value,s[i+1].value,s[i+2].value)) == 1){printf("The Winner is x!\n");gamestate.state=2;} } if((sum(s[0].value,s[4].value,s[8].value)) == 8){printf("The Winner is o!\n");gamestate.state=1;} if((sum(s[0].value,s[4].value,s[8].value)) == 1){printf("The Winner is x!\n");gamestate.state=2;} if((sum(s[2].value,s[4].value,s[6].value)) == 8){printf("The Winner is o!\n");gamestate.state=1;} if((sum(s[2].value,s[4].value,s[6].value)) == 1){printf("The Winner is x!\n");gamestate.state=2;} } void playGame(){ // start playing the game gamestate.state = 3; //set-up the gamestate srand(time(NULL)); int temp = (rand()%2) + 1; if(temp == 2){ // if two comp goes first temp = (rand()%2) + 1; if(temp == 2){ s[4].value = 2; s[4].sign = 'o'; gamestate.moves++; }else{ s[2].value = 2; s[2].sign = 'o'; gamestate.moves++; } } displayBoard(); while(gamestate.state == 3){ if(gamestate.moves<10); getHumanMove(); if(gamestate.moves<10); getCompMove(); checkWinner(); if(gamestate.state == 3 && gamestate.moves==9){ printf("The game is a tie :p\n"); break; } displayBoard(); } } int main(int argc, const char *argv[]){ printf("Welcome to Tic Tac Toe\nby The Elite Noob\nEnter 1-9 To play a move, standard numpad\n1 is bottom-left, 9 is top-right\n"); while(1){ // while game is being played printf("\nPress 1 to play a new game, or any other number to exit;\n>>:"); char line[255]; // input whether or not to play the game fgets(line, sizeof(line), stdin); int choice; // user's choice about playing or not while(sscanf(line, "%d", &choice) != 1) { //1 match of defined specifier on input line printf("Sorry, that's not a valid option!\n"); fgets(line, sizeof(line), stdin); } if(choice == 1){ setUpGame(); // set's up the game playGame(); // Play a Game }else {break;} // exit the application } printf("\nThank's For playing!\nHave a good Day!\n"); return 0; }

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  • Self-documenting code vs Javadocs?

    - by Andiaz
    Recently I've been working on refactoring parts of the code base I'm currently dealing with - not only to understand it better myself, but also to make it easier for others who are working on the code. I tend to lean on the side of thinking that self-documenting code is nice. I just think it's cleaner and if the code speaks for itself, well... That's great. On the other hand we have documentation such as javadocs. I like this as well, but there's a certain risk that comments here gets outdated (as well as comments in general of course). However, if they are up-to-date they can be extremely useful of say, understanding a complex algorithm. What are the best practices for this? Where do you draw the line between self-documenting code and javadocs?

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  • Should I forward the a call to .Equals onto .Equals<T>?

    - by Jaimal Chohan
    So, I've got you bog standard c# object, overriding Equalsand implementing IEquatable public override int GetHashCode() { return _name.GetHashCode(); } public override bool Equals(object obj) { return Equals(obj as Tag) } #region IEquatable<Tag> Members public bool Equals(Tag other) { if (other == null) return false; else return _name == other._name; } #endregion Now, for some reason, I used to think that forwarding the calls from Equals into Equals was bad, no idea why, perhaps I read it a long time ago, anyway I'd write separate (but logically same) code for each method. Now I think forwarding Equals to Equals is okay, for obvious reasons, but for the life me I can't remember why I thought it wasn't before. Any thoughts?

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  • Where to find algorithms work?

    - by Misha
    The funnest parts of my projects have been the back-end algorithms work. I have worked on projects where I implemented Gaussian Mixture models, a Remez algorithm and a few Monte Carlo schemes. I loved figuring out how these processes worked and tuning them when they didn't. I recently graduated and my problem lies in the work I was able to find. The only jobs I have found, with my Electrical Engineering degree, are for writing user applications. Tasks such as fashioning web interfaces or front-ends for hardware devices. When I speak with potential employers about my interests they say they have no work of the sort. Where does one find work that involves implementing these kind of schemes?

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  • In centralized version control, is it always good to update often?

    - by janos
    Assuming that: You are in a team developing some software. Your team is using centralized version control in the development process. You are working on a new feature which will surely take several days to complete, and you won't be able to commit before that because it would break the build. Your team members commit something every day that affects some of the files you're working with for your fancy new feature. Since this is centralized version control, you will have to update your local checkout at some point: at least once right before committing the new feature. If you update only once right before your commit, then there might be a lot of conflicts due to the many other changes by your teammates, which could be a world of pain to resolve all at once. Or, you could update often, and even if there are a few conflicts to resolve day by day, it should be easier to do, little by little. Can we say that it is always a good idea to update often?

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  • Which prediction model for web page recommendation?

    - by Nilesh
    I am trying to implement a web page recommendation wherein registered users will be given a recommendation of which page to visit depending upon the previous data.So with initial study I decided to go on with clustering the data with rough sets and then will move forward to find out the sequential patters with the use of prefix span algorithm.So now I want to have a better prediction model in place which can predict the access frequency of pages.I have figured out with Markov model but still some more suggestions will be valuable.Also please help me with some references of the models too.Is it possible to directly predict the next page access with the result of PrefixSpan.If so how?

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  • DDD and validation of aggregate root

    - by Mik378
    Suppose an aggregate root : MailConfiguration (wrapping an AddressPart object). The AddressPart object is a simple immutable value object with some fields like senderAdress, recipentAddress (to make example simple). As being an invariant object, AddressPart should logically wrap its own Validator (by the way of external a kind of AddressValidator for respecting Single Responsibility Principle) I read some articles that claimed an aggregateRoot must validate its 'children'. However, if we follow this principle, one could create an AddressPart with an uncohesive/invalid state. What are your opinion? Should I move the collaborator AddressValidator(used in constructor so in order to validate immediately the cohesion of an AddressPart) from AddressPart and assign it to aggregateRoot (MailConfiguration) ?

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  • Do you leverage the benefits of the open-closed principle?

    - by Kaleb Pederson
    The open-closed principle (OCP) states that an object should be open for extension but closed for modification. I believe I understand it and use it in conjunction with SRP to create classes that do only one thing. And, I try to create many small methods that make it possible to extract out all the behavior controls into methods that may be extended or overridden in some subclass. Thus, I end up with classes that have many extension points, be it through: dependency injection and composition, events, delegation, etc. Consider the following a simple, extendable class: class PaycheckCalculator { // ... protected decimal GetOvertimeFactor() { return 2.0M; } } Now say, for example, that the OvertimeFactor changes to 1.5. Since the above class was designed to be extended, I can easily subclass and return a different OvertimeFactor. But... despite the class being designed for extension and adhering to OCP, I'll modify the single method in question, rather than subclassing and overridding the method in question and then re-wiring my objects in my IoC container. As a result I've violated part of what OCP attempts to accomplish. It feels like I'm just being lazy because the above is a bit easier. Am I misunderstanding OCP? Should I really be doing something different? Do you leverage the benefits of OCP differently? Update: based on the answers it looks like this contrived example is a poor one for a number of different reasons. The main intent of the example was to demonstrate that the class was designed to be extended by providing methods that when overridden would alter the behavior of public methods without the need for changing internal or private code. Still, I definitely misunderstood OCP.

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  • Pause and Resume and get the value of a countdown timer by savedInstanceState [closed]

    - by Catherine grace Balauro
    I have developed a countdown timer and I am not sure how to pause and resume the timer as the TextView for the timer is being clicked. Click to start then click again to pause and to resume, click again the timer's text view. This is my code: Timer = (TextView)this.findViewById(R.id.time); //TIMER Timer.setOnClickListener(TimerClickListener); counter = new MyCount(600000, 1000); }//end of create private OnClickListener TimerClickListener = new OnClickListener() { public void onClick(View v) { updateTimeTask(); } private void updateTimeTask() { if (decision==0){ counter.start(); decision=1;} else if(decision==2){ counter.onResume1(); decision=1; } else{ counter.onPause1(); decision=2; }//end if }; }; class MyCount extends CountDownTimer { public MyCount(long millisInFuture, long countDownInterval) { super(millisInFuture, countDownInterval); }//MyCount public void onResume1(){ onResume(); } public void onPause1() { onPause();} public void onFinish() { Timer.setText("00:00"); p1++; if (p1<=4){ TextView PScore = (TextView) findViewById(R.id.pscore); PScore.setText(p1 + ""); }//end if }//finish public void onTick(long millisUntilFinished) { Integer milisec = new Integer(new Double(millisUntilFinished).intValue()); Integer cd_secs = milisec / 1000; Integer minutes = (cd_secs % 3600) / 60; Integer seconds = (cd_secs % 3600) % 60; Timer.setText(String.format("%02d", minutes) + ":" + String.format("%02d", seconds)); //long timeLeft = millisUntilFinished / 1000; }//on tick }//class MyCount protected void onResume() { super.onResume(); //handler.removeCallbacks(updateTimeTask); //handler.postDelayed(updateTimeTask, 1000); }//onResume @Override protected void onPause() { super.onPause(); //do stuff }//onPause I am only beginner in android programming and I don't know how to get the value of the countdown timer using savedInstanceState. How do I do this?

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  • Why should a class be anything other than "abstract" or "final/sealed"

    - by Nicolas Repiquet
    After 10+ years of java/c# programming, I find myself creating either: abstract classes: contract not meant to be instantiated as-is. final/sealed classes: implementation not meant to serve as base class to something else. I can't think of any situation where a simple "class" (i.e. neither abstract nor final/sealed) would be "wise programming". Why should a class be anything other than "abstract" or "final/sealed" ? EDIT This great article explains my concerns far better than I can.

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  • Placing of copyright notice in source code

    - by Diana Dcn
    I'm about to release a project of mine that I'm really proud of under the GNU GPL and I have some questions: Should one attach a copyright notice on each and every source code file from their project? I think it's a bit ridiculous to claim copyright on a 3 line abstract class. Should I attach a copyright notice only to really important source code files? Can I not attach the whole standard thingy? Because it's big and bulky and gets in the way... If so, is the variant below ok/enough? Copyright year firstname lastname. This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation.

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  • How to switch from developer to dba? [on hold]

    - by lamwaiman1988
    I am working as a developer for 3 years and I am thinking of switch to dba. I do not own any certificate nor received any training regarding the daily job of dba. My company also do not offer any chance of work/training related to a dba. If I want to be a dba ( because of the salary and a much stable job than developer ), should I go to get some oracle certificates? I've also heard that you can't be a good dba if you cannot get a good understanding about the working OS such as windows/unix ( and to do that you also need to get some certificate on windows administration or unix administration ) but they recommend book of Rich Stevens over certificate. I am confused on what should I do to make this happen.

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  • Microsoft Public License Question

    - by ryanzec
    Let preface this by saying that I understand that any advice I may receive is not to be taken as 100% correct, I am just looking for what people's understand of what this license is. I have been looking for a library that allow be to deal with archived compressed files (like zip files) and so far the best one I have found is DotNetZip. The only concern I have is that I am not familiar with the Microsoft Public License. While I plan to release a portion of my project (a web application platform) freely (MIT/BSD style) there are a few things. One is that I don't plan on actually releasing the source code, just the compiled project. Another thing is that I don't plan on releasing everything freely, only a subset of the application. Those are reason why I stay away form (L)GPL code. Is this something allowed while using 3rd party libraries that are licensed under the Microsoft Public License? EDIT The part about the Microsoft license that concerns me is Section 3 (D) which says (full license here): If you distribute any portion of the software in source code form, you may do so only under this license by including a complete copy of this license with your distribution. If you distribute any portion of the software in compiled or object code form, you may only do so under a license that complies with this license. I don't know what is meant by 'software'. My assumption would be that 'software' only refers to the library included under the license (being DotNetZip) and that is doesn't extends over to my code which includes the DotNetZip library. If that is the case then everything is fine as I have no issues keeping the license for DotNetZip when release this project in compiled form while having my code under its own license. If 'software' also include my code that include the DotNetZip library then that would be an issue (as it would basically act like GPL with the copyleft sense).

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  • advice for a new software engineer/developer right out of college

    - by ranzy
    I just graduated recently from a 4-year university with a degree in Computer Science and thankfully got a job in Software Engineering. I'm working with C++ with a .NET framework if that's correct to say because that also confuses me. What I'm asking for is what tutorials/books are out there to learn C++ for Windows Programming I guess? I know how to program somewhat and I understand the concepts but when I look at the code it doesn't make sense to me. I know I just started so it's kind of expected but it's certainly quite different from college. Thanks!

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  • GCC: assembly listing for IA64 without an Itanium machine

    - by KD04
    I need to try the following thing: I would like to compile some simple C code samples and see the assembly listing generated by GCC for IA64 architecture, i.e. I just want to run GCC with the -S switch and see the resultant .s file. I don't have an Itanium machine, so in order to do it myself I'll probably need a cross-compiling version of GCC built for x86 RedHat. I'm not interested in full cross-compilation, meaning that I don't need to generate the binaries at all. The easiest way, of course, would be to find an Itanium machine with with GCC and just try it there. Unfortunately, I don't seem to have access to any. Another option is to build a cross-compiling version GCC on my RedHat, but apparently that's quite an endeavor for someone who hasn't done it before (I assume that the fact that I only need .s output doesn't make it simpler). What other options are there, if any? Maybe there's some sort of a web front to an Itanium GCC compiler on the Net (something like Comeau Online or ideone.com, but with .s output)? Anything else? I would appreciate any help.

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  • Building a template engine - starting point

    - by Anirudh
    We're building a Django-based project with a template component. This component will be separate from the project as such and can be Django/Python, Node, Java or whatever works. The template has to be rendered into HTML. The templates will contain references to objects with properties that are defined in the DB, say, a Bus. For eg, it could be something like [object type="vehicle" weight="heavy"] and it would have to pull a random object from the DB fulfilling the criteria : type="vehicle" weight="heavy" (bus/truck/jet) and then substitute that tag with an image, say, of a Bus. Also it would have to be able to handle some processing. Eg: What is [X type="integer" lte="10"] + [Y type="integer" lte="10"] [option X+Y correct_ans="true"] [option X-Y correct_ans="false"] [option X+y+1 correct_ans="false"] The engine would be expected to fill in a random integer value <= 10 for X and Y and show radioboxes for each of the options. Would also have to store the fact that the first option is the correct answer. Does it to make sense to write something from the scratch? Or is it better to use an existing templating system (like Django's own templating system) as a starting point? Any suggestions on how I can approach this?

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  • How to handle encryption key conflicts when synchronizing data?

    - by Rafael
    Assume that there is data that gets synchronized between several devices. The data is protected with a symmetric encryption algorithm and a key. The key is stored on each device and encrypted with a password. When a user changes the password only the key gets re-encrypted. Under normal circumstances, when there is a good network connection to other peers, the current key gets synchronized and all data on the new device gets encrypted with the same key. But how to handle situations where a new device doesn’t have a network connection and e.g. creates its own new, but incompatible key? How to keep the usability as high as possible under such circumstances? The application could detect that there is no network and hence refuse to start. That’s very bad usability in my opinion, because the application isn’t functional at all in this case. I don’t consider this a solution. The application could ignore the missing network connection and create a new key. But what to do when the application gains a network connection? There will be several incompatible keys and some parts of the underlying data could only be encrypted with one key and other parts with another key. The situation would get worse if there would be more keys than just two and the application would’ve to ask every time for a password when another object that should get decrypted with another key would be needed. It is very messy and time consuming to try to re-encrypt all data that is encrypted with another key with a main key. What should be the main key at all in this case? The oldest key? The key with the most encrypted objects? What if the key got synchronized but not all objects that got encrypted with this particular key? How should the user know for which particular password the application asks and why it takes probably very long to re-encrypt the data? It’s very hard to describe encryption “issues” to users. So far I didn’t find an acceptable solution, nor some kind of generic strategy. Do you have some hints about a concrete strategy or some books / papers that describe synchronization of symmetrically encrypted data with keys that could cause conflicts?

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