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• When designing an event, is it a good idea to prevent listeners from being added twice?

  - by Matt

  I am creating an event-based API where a user can subscribe to an event by adding listener objects (as is common in Java or C#). When the event is raised, all subscribed listeners are invoked with the event information. I initially decided to prevent adding an event listener more than once. If a listener is added that already exists in the listener collection, it is not added again. However, after thinking about it some more, it doesn't seem that most event-based structures actually prevent this. Was my initial instinct wrong? I'm not sure which way to go here. I guess I thought that preventing addition of an existing listener would help to avoid a common programming error. Then again, it could also hide a bug that would lead to code being run multiple times when it shouldn't.

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• Python design mistakes

  - by Andrea

  A while ago, when I was learning Javascript, I studied Javascript: the good parts, and I particularly enjoyed the chapters on the bad and the ugly parts. Of course, I did not agree with everything, as summing up the design defects of a programming language is to a certain extent subjective - although, for instance, I guess everyone would agree that the keyword with was a mistake in Javascript. Nevertheless, I find it useful to read such reviews: even if one does not agree, there is a lot to learn. Is there a blog entry or some book describing design mistakes for Python? For instance I guess some people would count the lack of tail call optimization a mistake; there may be other issues (or non-issues) which are worth learning about.

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• Talking to a server in Win32; how do I see the server's response?

  - by Vinod K

  I am new to Win32 programming. sprintf(lpszBuff,"HELO Mail-Server\r\n"); send(s,lpszBuff,strlen(lpszBuff),0); recv(s,lpszBuff,100,0); cout << lpszBuff; In here I connect to a local mail server. The buffer contains the request I send, the same buffer contains the reply send by the browser. How do I see the reply? cout <<buffer doesn't show any output. I am doing this on VC++ 2008.

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• C++ Types Impossible to Name

  - by Kirakun

  While reading Wikipedia's page on decltype, I was curious about the statement, Its [decltype's] primary intended use is in generic programming, where it is often difficult, or even impossible, to name types that depend on template parameters. While I can understand the difficulty part of that statement, what is an example where there is a need to name a type that cannot be named under C++03? EDIT: My point is that since everything in C++ has a declaration of types. Why would there ever be a case where it is impossible to name a type? Furthermore, aren't trait classes designed to yield type informations? Could trait classes be an alternative to decltype?

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• What workflow should I use for JavaScript editing?

  - by Patrick

  Warning: I have very little JavsScript experience. In my past programming experience, I usually have a standalone interpreter/compiler, a text editor and a command line to compile/run my software or my tests (I love test driven development). I really like it this way, since I have the feeling of being in complete control over the tools. However, editing JavaScript I need to put statements in a text file , open my web browser and click on reload. I don't feel comfortable with it, as I cannot really see what is going on (besides some alert boxes). Can you suggest me (I'm on a Mac) another workflow? Perhaps with a debugger? Is there a standalone JavaScript interpreter?

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• C++ private pointer "leaking"?

  - by jbu

  I'm going to create a class to hold a long list of parameters that will be passed to a function. Let's use this shorter example: class ParamList{ public: ParamList(string& a_string); string& getString(); //returns my_string private: string& my_string; } My question is this: my_string is private, yet I'm returning the reference to it. Isn't that called something like private pointer leaking in C++? Is this not good programming practice? I want callers of getString to be able to get the reference and also modify it. Please let me know. Thanks, jbu edit1: callers will use getString() and modify the string that was returned.

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• What is the best platform/language for a 3D game in a web browser?

  - by CodeJustin.com

  I have enjoyed making 2D games in various langues (actionscript 3.0, java, python, others) but now I'm ready to move into 3D and to really get me amped up while learning 3D development I'm going to attempt to make a 3D multiplayer game (I already have server written in python). I'm looking for a platform that will run a 3D game well in the browser on low end computers with low end internet. What first came to mind was try Java or use flash/silver light with a 3D framework but I wanted to ask the good people of stackoverflow since performance is a big part of my needs and also good documentation is a plus since I'm just starting 3D development. (the programming language does not matter)

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• Third Party Libraries and Technologies very Java Programmer must be aware of?

  - by kunjaan

  I agree that this is a very subjective question but as a student of Java , I get suggested good libraries and technologies for Java by my mentors at work. For example, I was not aware of Google Guice for Dependency Injection, awesomeness of Java Reflection APIs, ORMs like Hibernate or stuffs you could do with libraries like Hadoop. I want to collect and share some of the libraries that exemplifies good java programming (so that beginners like me could code walk and emulate the coding practice), teach unique concepts to Java (for example Dependency Injections or ORM) and/or are really interesting libraries that a student like me would get to do interesting projects on (eg. Hadoop). I redited this question 3 times to make it more specific : ). I am sorry if I am really not clear in my intentions. But some kind of a list of good concepts and third party libraries for Java could really help some of my intern friends here at work. Thank you.

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• Could someone tell me if my C++ indent style is named? (example given)

  - by Maulrus

  I'm learning C++. For me, my programming style is just what looks the best; it doesn't seem to follow the rules of any one particular style. Here's an example void f(int x){ //no space between close-paren and bracket if (!x){ cout << "x is non-zero\n"; } //closing bracket indented to the same level as the original statement } It's only slightly different for something like a class or a namespace: class myClass {}; //space between class name and bracket, otherwise the same as functions K&R style does uses that kind of bracketing for statements, but my style uses it for everything. I'd like to know if there's a name for it so I can say simply what my indent style is without having to explain using examples like these.

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• Printing python tkinter output

  - by Eric

  I am trying to print the contents of a python tkinter canvas. I have tried using the postscript method of canvas to create a postscript file, but I get a blank page. I know this is because I have embedded widgets, and these do not get rendered by the postscript method. Before I rewrite my program to create a more printer-friendly layout, can someone suggest a way to approach this problem? All of the programming books I have ever read approach the problem of sending output to a printer with a bit of hand-waving, something along the lines of: "It's a difficult problem that depends on interacting with the operating system." I also have a hard time finding resources about this because of all the pages related to printing to the screen. I am using Python 2.6, on Ubuntu 9.04.

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• Access static constant variable from multiple threads in C

  - by user325519

  I have some experience with multithread programming under Linux (C/C++ & POSIX threads), however most obvious cases are sometimes very complicated. I have several static constant variables (global and function local) in my code, can I access them simultaneously from multiple threads without using mutexes? Because I don't modify them it should be ok, but it's always better to ask. I have to do heavy speed optimization, so even as fast operations as mutex lock/unlock are quite expensive for me, especially because my application is going to access these variables form long loops.

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• Adding a Jar to ext and using it in Eclipse

  - by Bob Breznak

  I am providing a client with a lab station image for a school program. There is a library that I'd like to directly add to the JRE so that students can use the library without needing to fiddle with adding the classpath. As this is a basic after school program, the goal is to just get students into programming with as little overhead additions as possible. At this point, I have the lib put into the jre/lib/ext and Eclipse is able to find it, however it will not allow access to any of the classes. I see it in the JRE System Library and the classes and packages are showing up there but when I go to use it, I am getting an "Access restriction" error. When I remove the JRE System Library then add it back in, everything works swimmingly. The library is accessible exactly as intended. Any ideas on how to resolve this?

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• Draw arrow on line

  - by Pete

  Hi, I have this code: CGPoint arrowMiddle = CGPointMake((arrowOne.x + arrowTo.x)/2, (arrowOne.y + arrowTo.y)/2); CGPoint arrowLeft = CGPointMake(arrowMiddle.x-40, arrowMiddle.y); CGPoint arrowRight = CGPointMake(arrowMiddle.x, arrowMiddle.y + 40); [arrowPath addLineToScreenPoint:arrowLeft]; [arrowPath addLineToScreenPoint:arrowMiddle]; [arrowPath addLineToScreenPoint:arrowRight]; [[mapContents overlay] addSublayer:arrowPath]; [arrowPath release]; with this output: http://yfrog.com/edschermafbeelding2010032p What have i to add to get the left and right the at same degree of the line + 30°. If someone has the algorithm of drawing an arrow on a line, pleas give it. It doesn't matter what programming language it is... Thanks

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• Is It Worth Using Bitwise Operators In Methods?

  - by user1626141

  I am very new to Java (and programming in general, my previous experience is with ActionScript 2.0 and some simple JavaScript), and I am working my way slowly and methodically through Java: A Beginner's Guide by Herbert Schildt. It is an incredible book. For one thing, I finally understand more-or-less what bitwise operators (which I first encountered in ActionScript 2.0) do, and that they are more efficient than other methods for certain sums. My question is, is it more efficient to use a method that uses, say, a shift right, to perform all your divisions/2 (or divisions/even) for you in a large program with many calculations (in this case, a sprawling RPG), or is it more efficient to simply use standard mathematical operations because the compiler will optimise it all for you? Or, am I asking the wrong question entirely?

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• C++ code generation for repeted task

  - by sateesh

  Hi, I have something like below which will get repeated many times based on the function that get called for e.g acceptfunction() { inserter["quantity"] = sdd.getfloat(quantity); inserter["prodtype"] = sdd.getstring(prodtype); : : so on } Like accept above there are 20 more functions(reject,cancel etc) which will do the similar thing.But the parameteres they insert can differ based on function called. How can I automate this kind of code.So that I dont need to write new function from scratch.Basically what I need is if i provide parametres like ("quantity",prodtype) through some text file or xml, it should generate the required function with the input parametres. Is this task can be handled through C++ tempalte Meta programming or someother code generation tool will help me to do this?

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• VBA long overflow

  - by HK_CH

  Hi I am trying to do some maths with my VBA excel (prime factorization) and I am hitting the limit of the long data type (runtime error 6 Overflow). Is there any way to get around this and still stay within VBA? (I am aware that the obvious one would be to use another more appropriate programming language) Thanks for help in advance! Thank you, it works in so far that I am able to get the big numbers into the variables now. However when I try to apply the MOD function (bignumber MOD 2 for example) it still fails with error message runtime error 6 Overflow.

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• Drawing unfilled rectangle shape in c++ openGL

  - by Bahaa

  I want to draw unfilled rectangle shape in openGL using c++ programming language but when I used the glBegin(GL_QUADS) or glBegin(GL_POLYGON), the resulted shape is filled but I want to be unfilled. How I can draw unfilled rectangle. void draweRect(void) { glClear(GL_COLOR_BUFFER_BIT); glColor3f(0.0,0.0,1.0); glLineWidth(30); glBegin(GL_POLYGON); glVertex2i(50,90); glVertex2i(100,90); glVertex2i(100,150); glVertex2i(50,150); glEnd(); glFlush(); }

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• What are the difference between Cygwin on windows and real UNIX environment

  - by Tarun

  Hi, I am a C/C++ developer. I have never done C++ programming on UNIX, I have done only on windows. I want to practice C++ on Unix. (Because all big companies ask C++ with Unix). I have a laptop on which i do not want to install any other OS (because i have installed very important software on it and i don't have setups) So, I searched and found CygWin which is Unix emulator for Windows. I am thinking to practice C++ on this. Please help me, how can I practice/learn in more close to the environment(Unix Environment) that is used in Big companies like IBM. What will be the difference between Unix and Cygwin?

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• HTTP server that handles requests through IO devices?

  - by StackedCrooked

  This question can probably only be answered for Unix-like systems that follow the "everything is a file" idiom. Would it be hard to create a web server that mounts local devices for handling http traffic? It would enable a program to read raw http requests from /dev/httpin (for example) and write the responses to /dev/httpout. I think this would be nice because it would allow me to create a web server from any programming language that is capable of handling IO streams. I don't really know where to start on this. Any suggestions on how to setup such a system?

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• (When) Does hardware, especially the CPU(s), deliver wrong results?

  - by sub

  What I'm talking about is: Is it possible that under certain circumstances the CPU "buggs" and suddenly responses 1+1=2? In which parts of the computer can that happen (HDD, RAM, Mainboard)? What could be the causes? Bad quality? Overheating? Does that even happen? When yes, how frequently? If everything is okay with the CPU (not a single fault in production, good temperature), can that still happen sometimes? What would be the results of, let's say one to three wrong computations? This is programming related as it would be nice to know if you can even rely on the hardware to return the right results.

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• Good real-world uses of metaclasses (e.g. in Python)

  - by Carles Barrobés

  I'm learning about metaclasses in Python. I think it is a very powerful technique, and I'm looking for good uses for them. I'd like some feedback of good useful real-world examples of using metaclasses. I'm not looking for example code on how to write a metaclass (there are plenty examples of useless metaclasses out there), but real examples where you have applied the technique and it was really the appropriate solution. The rule is: no theoretical possibilities, but metaclasses at work in a real application. I'll start with the one example I know: Django models, for declarative programming, where the base class Model uses a metaclass to fill the model objects of useful ORM functionality from the attribute definitions. Looking forward to your contributions.

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• Major inconsistencies in Zend Framework

  - by John Nall

  Okay first of all let me just say Zend Framework is the greatest tool I have ever used in 30+ years of programming (well, for web development, Qt wins the desktop market). However, through my use I have noticed some glaring and annoying inconsistencies. For instance, Zend_Form_Element's have a setAttrib() method. Now why the hell is this the only method in that API which is abbrev.? Why then am I using setRequired() instead of setReq()? I have more examples, I am extremely nerd raged about this. It is completely ruining what could have been God's gift to web development. FOR FUTURE REFERENCE NEVER ABBREV. THINGS WHEN MAKING AN API. also always filter data before storing it i m o Who do we talk to about this, where something will actually get done about it?

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• How compiling circular dependencies works?

  - by Fabio F.

  I've made the example in Java but I think (not tested) that it works in other (all?) languages. You have 2 files M.java that says public class MType{ XType x; MType(){ x = null;} } and another file XType.java (in the same directory) public class XType{ MType m; public XType(MType m){ this.m=m;} } Ok it's BAD programming , but.. if you run javac XType it compiles: compiles even MTypes because XType needs it. But.. MType needs XType.. how it works? How does the compiler know what is happening? Probably is a stupid question, but I would like to know how the compiler (javac or other compilers if you know.) manages that situation, not how to avoid it. I'm asking because i'm writing a precompiler and I would like to manage that situation.. Thank you

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• What can't the NDK be used for?

  - by Android Eve

  From the official NDK site: The Android NDK... provides headers and libraries that allow you to build activities, handle user input, use hardware sensors, access application resources, and more, when programming in C or C++. If you write native code, your applications are still packaged into an .apk file and they still run inside of a virtual machine on the device. The fundamental Android application model does not change. Yet, it is always described as a companion tool to the Android SDK and as a toolset that allows to "implement parts of your applications using native-code languages such as C and C++". My understanding from this is that, unlike the Java based SDK, the NDK is not designed to implement certain parts of an Android application. Is this correct? If so, what parts doesn't the NDK allow implementing?

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• Practise Questions for Templates,Functors,CallBack functions in c++?

  - by Eternal Learner

  Hi, I have been reading templates,functors,callback function for the past week and have referred some good books and articles. I however feel that, unless I can get good practice - programming in templates and use functors-callbacks there is no way I can really understand all the concepts or fluently use them while coding. Could anyone suggest some articles or books or websites where , there is a definition of the problem and also a solution to the same. I could just write code for the problem and check later on if my solution is good enough.. I am also aware that some of our stack-overflow members are experts in templates and callback functions. It would be great if they could design a problem and also post a solution , where a lot of template beginners like me could benefit.

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