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• Are there any downsides in using C++ for network daemons?

  - by badcat

  Hey guys! I've been writing a number of network daemons in different languages over the past years, and now I'm about to start a new project which requires a new custom implementation of a properitary network protocol. The said protocol is pretty simple - some basic JSON formatted messages which are transmitted in some basic frame wrapping to have clients know that a message arrived completely and is ready to be parsed. The daemon will need to handle a number of connections (about 200 at the same time) and do some management of them and pass messages along, like in a chat room. In the past I've been using mostly C++ to write my daemons. Often with the Qt4 framework (the network parts, not the GUI parts!), because that's what I also used for the rest of the projects and it was simple to do and very portable. This usually worked just fine, and I didn't have much trouble. Being a Linux administrator for a good while now, I noticed that most of the network daemons in the wild are written in plain C (of course some are written in other languages, too, but I get the feeling that 80% of the daemons are written in plain C). Now I wonder why that is. Is this due to a pure historic UNIX background (like KISS) or for plain portability or reduction of bloat? What are the reasons to not use C++ or any "higher level" languages for things like daemons? Thanks in advance! Update 1: For me using C++ usually is more convenient because of the fact that I have objects which have getter and setter methods and such. Plain C's "context" objects can be a real pain at some point - especially when you are used to object oriented programming. Yes, I'm aware that C++ is a superset of C, and that C code is basically C++. But that's not the point. ;)

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• How do you use stl's functions like for_each?

  - by thomas-gies

  I started using stl containers because they came in very handy when I needed functionality of a list, set and map and had nothing else available in my programming environment. I did not care much about the ideas behind it. STL documentations were only interesting up to the point where it came to functions, etc. Then I skipped reading and just used the containers. But yesterday, still being relaxed from my holidays, I just gave it a try and wanted to go a bit more the stl way. So I used the transform function (can I have a little bit of applause for me, thank you). From an academic point of view it really looked interesting and it worked. But the thing that boroughs me is that if you intensify the use of those functions, you need 10ks of helper classes for mostly everything you want to do in your code. The hole logic of the program is sliced in tiny pieces. This slicing is not the result of god coding habits. It's just a technical need. Something, that makes my life probably harder not easier. And I learned the hard way, that you should always choose the simplest approach that solves the problem at hand. And I can't see what, for example, the for_each function is doing for me that justifies the use of a helper class over several simple lines of code that sit inside a normal loop so that everybody can see what is going on. I would like to know, what you are thinking about my concerns? Did you see it like I do when you started working this way and have changed your mind when you got used to it? Are there benefits that I overlooked? Or do you just ignore this stuff as I did (and will go an doing it, probably). Thanks. PS: I know that there is a real for_each loop in boost. But I ignore it here since it is just a convenient way for my usual loops with iterators I guess.

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• Ruby: counters, counting and incrementing

  - by Shyam

  Hi, If you have seen my previous questions, you'd already know I am a big nuby when it comes to Ruby. So, I discovered this website which is intended for C programming, but I thought whatever one can do in C, must be possible in Ruby (and more readable too). The challenge is to print out a bunch of numbers. I discovered this nifty method .upto() and I used a block (and actually understanding its purpose). However, in IRb, I got some unexpected behavior. class MyCounter def run 1.upto(10) { |x| print x.to_s + " " } end end irb(main):033:0> q = MyCounter.new => #<MyCounter:0x5dca0> irb(main):034:0> q.run 1 2 3 4 5 6 7 8 9 10 => 1 I have no idea where the = 1 comes from :S Should I do this otherwise? I am expecting to have this result: 1 2 3 4 5 6 7 8 9 10 Thank you for your answers, comments and feedback!

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• Is it OK to write code after [super dealloc]? (Objective-C)

  - by Richard J. Ross III

  I have a situation in my code, where I cannot clean up my classes objects without first calling [super dealloc]. It is something like this: // Baseclass.m @implmentation Baseclass ... -(void) dealloc { [self _removeAllData]; [aVariableThatBelongsToMe release]; [anotherVariableThatBelongsToMe release]; [super dealloc]; } ... @end This works great. My problem is, when I went to subclass this huge and nasty class (over 2000 lines of gross code), I ran into a problem: when I released my objects before calling [super dealloc] I had zombies running through the code that were activated when I called the [self _removeAllData] method. // Subclass.m @implementation Subclass ... -(void) deallloc { [super dealloc]; [someObjectUsedInTheRemoveAllDataMethod release]; } ... @end This works great, and It didn't require me to refactor any code. My question Is this: Is it safe for me to do this, or should I refactor my code? Or maybe autorelease the objects? I am programming for iPhone if that matters any.

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• Freelance web hosting - what are good LAMP choices?

  - by tkotitan

  I think it's best if I ask this question with an example scenario. Let's say your mom-and-pop local hardware store has never had a website, and they want you, the freelance developer to build them a website. You have all the skills to run a LAMP setup and admin a system, so the difficult question you ask yourself is - where will I host it? As you aren't going to host it out of the machine in your apartment. Let's say you want to be able to customize your own system, install the version of PHP you want, and manage your own database. Perhaps the best kind of hosting is to get a virtual machine so you can customize the system as you see fit. But this essentially a "set it and forget it" site you make, bill by the hour for, and then are done. In other words, the hosting should not be an issue. Given the requirements of hosting a website: Unlimited growth potential needing good amounts of bandwidth to handle visitors Wide range of system and programming options allowing it to be portable Relatively cheap (not necessarily the cheapest) or reasonable scaling cost Reliable hosting with good support Hosted entirely on the host company's hardware Who would you pick to host this website? Yes I am asking for a business/company recommendation. Is there a clear answer for this scenario, or a good source that can reliably give the current answer? I know there are all kinds of schemes out there. I'm just wondering if any one company fills the bill for freelancers and stands out in such a crowded market.

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• Help! I'm a Haskell Newbie

  - by Darknight

  I've only just dipped my toe in the world of Haskell as part of my journey of programming enlightenment (moving on from, procedural to OOP to concurrent to now functional). I've been trying an online Haskell Evaluator. However I'm now stuck on a problem: Create a simple function that gives the total sum of an array of numbers. In a procedural language this for me is easy enough (using recursion) (c#) : private int sum(ArrayList x, int i) { if (!(x.Count < i + 1)) { int t = 0; t = x.Item(i); t = sum(x, i + 1) + t; return t; } } All very fine however my failed attempt at Haskell was thus: let sum x = x+sum in map sum [1..10] this resulted in the following error (from that above mentioned website): Occurs check: cannot construct the infinite type: a = a -> t Please bear in mind I've only used Haskell for the last 30 minutes! I'm not looking simply for an answer but a more explanation of it. Thanks in advanced.

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• Alter a function as a parameter before evaluating it in R?

  - by Shane

  Is there any way, given a function passed as a parameter, to alter its input parameter string before evaluating it? Here's pseudo-code for what I'm hoping to achieve: test.func <- function(a, b) { # here I want to alter the b expression before evaluating it: b(..., val1=a) } Given the function call passed to b, I want to add in a as another parameter without needing to always specify ... in the b call. So the output from this test.func call should be: test.func(a="a", b=paste(1, 2)) "1" "2" "a" Edit: Another way I could see doing something like this would be if I could assign the additional parameter within the scope of the parent function (again, as pseudo-code); in this case a would be within the scope of t1 and hence t2, but not globally assigned: t2 <- function(...) { paste(a=a, ...) } t1 <- function(a, b) { local( { a <<- a; b } ) } t1(a="a", b=t2(1, 2)) This is somewhat akin to currying in that I'm nesting the parameter within the function itself. Edit 2: Just to add one more comment to this: I realize that one related approach could be to use "prototype-based programming" such that things would be inherited (which could be achieved with the proto package). But I was hoping for a easier way to simply alter the input parameters before evaluating in R.

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• Parallelize or vectorize all-against-all operation on a large number of matrices?

  - by reve_etrange

  I have approximately 5,000 matrices with the same number of rows and varying numbers of columns (20 x ~200). Each of these matrices must be compared against every other in a dynamic programming algorithm. In this question, I asked how to perform the comparison quickly and was given an excellent answer involving a 2D convolution. Serially, iteratively applying that method, like so list = who('data_matrix_prefix*') H = cell(numel(list),numel(list)); for i=1:numel(list) for j=1:numel(list) if i ~= j eval([ 'H{i,j} = compare(' char(list(i)) ',' char(list(j)) ');']); end end end is fast for small subsets of the data (e.g. for 9 matrices, 9*9 - 9 = 72 calls are made in ~1 s). However, operating on all the data requires almost 25 million calls. I have also tried using deal() to make a cell array composed entirely of the next element in data, so I could use cellfun() in a single loop: # who(), load() and struct2cell() calls place k data matrices in a 1D cell array called data. nextData = cell(k,1); for i=1:k [nextData{:}] = deal(data{i}); H{:,i} = cellfun(@compare,data,nextData,'UniformOutput',false); end Unfortunately, this is not really any faster, because all the time is in compare(). Both of these code examples seem ill-suited for parallelization. I'm having trouble figuring out how to make my variables sliced. compare() is totally vectorized; it uses matrix multiplication and conv2() exclusively (I am under the impression that all of these operations, including the cellfun(), should be multithreaded in MATLAB?). Does anyone see a (explicitly) parallelized solution or better vectorization of the problem?

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• SYN receives RST,ACK very frequently

  - by user1289508

  Hi Socket Programming experts, I am writing a proxy server on Linux for SQL Database server running on Windows. The proxy is coded using bsd sockets and in C, and it is working just fine. When I use a database client (written in JAVA, and running on a Linux box) to fire queries (with a concurrency of 100 or more) directly to the Database server, not experiencing connection resets. But through my proxy I am experiencing many connection resets. Digging deeper I came to know that connection from 'DB client' to 'Proxy' always succeeds but when the 'Proxy' tries to connect to the DB server the connection fails, due to the SYN packet getting RST,ACK. That was to give some background. The question is : Why does sometimes SYN receives RST,ACK? 'DB client(linux)' to 'Server(windows)' ---- Works fine 'DB client(linux) to 'Proxy(Linux)' to 'Server(windows)' ----- problematic I am aware that this can happen in "connection refused" case but this definitely is not that one. SYN flooding might be another scenario, but that does not explain fine behavior while firing to Server directly. I am suspecting some socket option setting may be required, that the client does before connecting and my proxy does not. Please put some light on this. Any help (links or pointers) is most appreciated. Additional info: Wrote a C client that does concurrent connections, which takes concurrency as an argument. Here are my observations: - At 5000 concurrency and above, some connects failed with 'connection refused'. - Below 2000, it works fine. But the actual problem is observed even at a concurrency of 100 or more. Note: The problem is time dependent sometimes it never comes at all and sometimes it is very frequent and DB client (directly to server) works fine at all times .

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• What is the best Networking implementation for my application?

  - by CaptainPhil

  I am in the planning phases of a project for myself, it is to be a single and multi-player card game. I would like to track statistics for each person such as world rankings etc... My problem is I do not know the best approach for the client - server architecture and programming. My original goal was to program everything in C# as I want to get proficient in that language. My original idea was to have a back-end database and a back end server run on some sort of hosting on the internet, however that seems costly for such a small project that may or may not make any money. I have tried looking into cloud services however I am unfamiliar with the technology, and I am not sure I can make them suit my needs, especially since most like Google's cloud wants you to use their coding architecture from what I understand. Finally my last problem is that I would like an architecture that can be used for different languages so that I can port it from PC to IPhone, Xbox etc... So does anyone have any advice on the best architecture and language to do this in? Am I worrying about architecture and back-end costs to much and should just concentrate on getting the game running any which way?

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• Finding k elements of length-n list that sum to less than t in O(nlogk) time

  - by tresbot

  This is from Programming Pearls ed. 2, Column 2, Problem 8: Given a set of n real numbers, a real number t, and an integer k, how quickly can you determine whether there exists a k-element subset of the set that sums to at most t? One easy solution is to sort and sum the first k elements, which is our best hope to find such a sum. However, in the solutions section Bentley alludes to a solution that takes nlog(k) time, though he gives no hints for how to find it. I've been struggling with this; one thought I had was to go through the list and add all the elements less than t/k (in O(n) time); say there are m1 < k such elements, and they sum to s1 < t. Then we are left needing k - m1 elements, so we can scan through the list again in O(n) time looking for all elements less than (t - s1)/(k - m1). Add in again, to get s2 and m2, then again if m2 < k, look for all elements less than (t - s2)/(k - m2). So: def kSubsetSumUnderT(inList, k, t): outList = [] s = 0 m = 0 while len(outList) < k: toJoin = [i for i in inList where i < (t - s)/(k - m)] if len(toJoin): if len(toJoin) >= k - m: toJoin.sort() if(s0 + sum(toJoin[0:(k - m - 1)]) < t: return True return False outList = outList + toJoin s += sum(toJoin) m += len(toJoin) else: return False My intuition is that this might be the O(nlog(k)) algorithm, but I am having a hard time proving it to myself. Thoughts?

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• Autoloading Development or Production configs (best practices)

  - by Xeoncross

  When programming sites you usually have one set of config files for the development environment and another set for the production server (or one file with both settings). I am assuming all projects should be handled by version control like git or svn. Manual file transfers (like FTP) is wrong on so many levels. How you enable/disable the correct settings (so that your system knows which ones to use) is a problem for me. Each system I work on just kind of jimmy-rigs a solution. Below are the 3 methods I know of and I am hoping that someone can submit a more elegant solutions. 1) File Based The system loads a folder structure based on the URL requested. /site.com /site.fakeTLD /lib index.php For example, if the url is http://site.com then the system loads the production config files located in the site.com folder. However, if I'm working on the site locally I visit http://site.fakeTLD to work on the local copy of the site. To setup this I edit my hosts file and add site.fakeTLD to point to my own computer (127.0.0.1/localhost) and then create a vhost in apache. So now I can work on the codebase locally and then push to the server without any trouble. The problem is that this is susceptible to a "host" injection attack. So someone loading site.com could set the host to site.fakeTLD and then the system would load my development config files instead of production. 2) Config Based The config files contain on section for development - and one for production. The problem is that each time you go to push your changes to the repo you have to edit the file to specify which set of config options should be used. $use = 'production'; //'development'; This leaves the repo open to human error should one of the developers forget to enable the right setting. 3) File System Check Based All the development machines have an extra empty file called "development.txt" or something. Each time the system loads it checks for this file - if found then it knows it is in development mode - if missing then it knows it is in production mode. Since the file is NEVER ADDED to the repo then it will never be pushed (and checked out) on the production machine. However, this just doesn't feel right and causes a slight slow down since all filesystem checks are slow. Is there anyway that the server can auto-detect wither to use the development or production configs?

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• What are five things you hate about your favorite language?

  - by brian d foy

  There's been a cluster of Perl-hate on Stackoverflow lately, so I thought I'd bring my "Five things you hate about your favorite language" question to StackOverflow. Take your favorite language and tell me five things you hate about it. Those might be things that just annoy you, admitted design flaws, recognized performance problems, or any other category. You just have to hate it, and it has to be your favorite language. Don't compare it to another language, and don't talk about languages that you already hate. Don't talk about the things you like in your favorite language. I just want to hear the things that you hate but tolerate so you can use all of the other stuff, and I want to hear it about the language you wished other people would use. I ask this whenever someone tries to push their favorite language on me, and sometimes as an interview question. If someone can't find five things to hate about his favorite tool, he don't know it well enough to either advocate it or pull in the big dollars using it. He hasn't used it in enough different situations to fully explore it. He's advocating it as a culture or religion, which means that if I don't choose his favorite technology, I'm wrong. I don't care that much which language you use. Don't want to use a particular language? Then don't. You go through due diligence to make an informed choice and still don't use it? Fine. Sometimes the right answer is "You have a strong programming team with good practices and a lot of experience in Bar. Changing to Foo would be stupid." This is a good question for code reviews too. People who really know a codebase will have all sorts of suggestions for it, and those who don't know it so well have non-specific complaints. I ask things like "If you could start over on this project, what would you do differently?" In this fantasy land, users and programmers get to complain about anything and everything they don't like. "I want a better interface", "I want to separate the model from the view", "I'd use this module instead of this other one", "I'd rename this set of methods", or whatever they really don't like about the current situation. That's how I get a handle on how much a particular developer knows about the codebase. It's also a clue about how much of the programmer's ego is tied up in what he's telling me. Hate isn't the only dimension of figuring out how much people know, but I've found it to be a pretty good one. The things that they hate also give me a clue how well they are thinking about the subject.

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• Variable sized packet structs with vectors

  - by Rev316

  Lately I've been diving into network programming, and I'm having some difficulty constructing a packet with a variable "data" property. Several prior questions have helped tremendously, but I'm still lacking some implementation details. I'm trying to avoid using variable sized arrays, and just use a vector. But I can't get it to be transmitted correctly, and I believe it's somewhere during serialization. Now for some code. Packet Header class Packet { public: void* Serialize(); bool Deserialize(void *message); unsigned int sender_id; unsigned int sequence_number; std::vector<char> data; }; Packet ImpL typedef struct { unsigned int sender_id; unsigned int sequence_number; std::vector<char> data; } Packet; void* Packet::Serialize(int size) { Packet* p = (Packet *) malloc(8 + 30); p->sender_id = htonl(this->sender_id); p->sequence_number = htonl(this->sequence_number); p->data.assign(size,'&'); //just for testing purposes } bool Packet::Deserialize(void *message) { Packet *s = (Packet*)message; this->sender_id = ntohl(s->sender_id); this->sequence_number = ntohl(s->sequence_number); this->data = s->data; } During execution, I simply create a packet, assign it's members, and send/receive accordingly. The above methods are only responsible for serialization. Unfortunately, the data never gets transferred. Couple of things to point out here. I'm guessing the malloc is wrong, but I'm not sure how else to compute it (i.e. what other value it would be). Other than that, I'm unsure of the proper way to use a vector in this fashion, and would love for someone to show me how (code examples please!) :) Edit: I've awarded the question to the most comprehensive answer regarding the implementation with a vector data property. Appreciate all the responses!

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• Design Technique: How to design a complex system for processing orders, products and units.

  - by Shyam

  Hi, Programming is fun: I learned that by trying out simple challenges, reading up some books and following some tutorials. I am able to grasp the concepts of writing with OO (I do so in Ruby), and write a bit of code myself. What bugs me though is that I feel re-inventing the wheel: I haven't followed an education or found a book (a free one that is) that explains me the why's instead of the how's, and I've learned from the A-team that it is the plan that makes it come together. So, armed with my nuby Ruby skills, I decided I wanted to program a virtual store. I figured out the following: My virtual Store will have: Products and Services Inventories Orders and Shipping Customers Now this isn't complex at all. With the help of some cool tools (CMapTools), I drew out some concepts, but quickly enough (thanks to my inferior experience in designing), my design started to bite me. My very first product-line were virtual "laptops". So, I created a class (Ruby): class Product attr_accessor :name, :price def initialize(name, price) @name = name @price = price end end which can be instantiated by doing (IRb) x = Product.new("Banana Pro", 250) Since I want my virtual customers to be able to purchase more than one product, or various types, I figured out I needed some kind of "Order" mechanism. class Order def initialize(order_no) @order_no = order_no @line_items = [] end def add_product(myproduct) @line_items << myproduct end def show_order() puts @order_no @line_items.each do |x| puts x.name.to_s + "\t" + x.price.to_s end end end that can be instantiated by doing (IRb) z = Order.new(1234) z.add_product(x) z.show_order Splendid, I have now a very simple ordering system that allows me to add products to an order. But, here comes my real question. What if I have three models of my product (economy, business, showoff)? Or have my products be composed out of separate units (bigger screen, nicer keyboard, different OS)? Surely I could make them three separate products, or add complexity to my product class, but I am looking for are best practices to design a flexible product object that can be used in the real world, to facilitate a complex system. My apologies if my grammar and my spelling are with error, as english is not my first language and I took the time to check as far I could understand and translate properly! Thank you for your answers, comments and feedback!

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• L-Soft LISTSERV TCPGUI Interface for PHP Creation

  - by poolnoodl

  I'm trying to use LISTSERV's "API" in PHP. L-Soft calls this TCPGUI, and essentially, you can request data like over Telnet. To do this, I'm using PHP's TCP socket functions. I've seen this done in other languages but can't quite convert it to PHP. I can connect, I can change set ASCII or BINARY mode. But I can never quite craft the header packet the way I need to authenticate, so I'm thinking I'm messing up my conversion. C: http://www.lsoft.com/manuals/16.0/htmlhelp/advanced%20topics/TCPGUI.html#2334328 $origin = '[email protected]'; $pwd = 'password'; $host = "example.com"; $port = 2306; $email = "[email protected]"; $list = "mailinglist"; $command = "Query $list FOR $email"; $fp = stream_socket_client("tcp://$host:$port", $errno, $errstr, 30); $cmd = $command . " PW=" . $pwd; $len = strlen($cmd); $orglen = strlen($origin); $n = $len + $orglen + 1; $headerPacket[0] = "1"; $headerPacket[1] = "B"; $headerPacket[2] = "\r"; $headerPacket[3] = "\n"; $headerPacket[4] = ord($n / 256); $headerPacket[5] = ord($n + 255); $headerPacket[6] = ord($orglen); for ($i = 0; $i < $orglen; $i++) { $headerPacket[$i + 7] = ord($origin[$i]); } for ($i = 0; $i < $len; $i++) { $cmdPacket[$i] = ord($cmd[$i]); } fwrite($fp, implode($headerPacket)); while (!feof($fp)) { echo fgets($fp, 1024); } Any thoughts on where I'm going wrong? I'd much appreciate it if anyone could point me toward some code to do this, days of googling and searching here on SO has only lead me to examples in other languages. Of course, if you know C (or Java or Perl as linked below in my comment to bypass the spam filter), PHP, and socket programming fairly well, you could probably rewrite the whole of the code in an hour, maybe a few minutes. You'd have my eternal thanks for that.

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• Java - is this an idiom or pattern, behavior classes with no state

  - by Berlin Brown

  I am trying to incorporate more functional programming idioms into my java development. One pattern that I like the most and avoids side effects is building classes that have behavior but they don't necessarily have any state. The behavior is locked into the methods but they only act on the parameters passed in. The code below is code I am trying to avoid: public class BadObject { private Map<String, String> data = new HashMap<String, String>(); public BadObject() { data.put("data", "data"); } /** * Act on the data class. But this is bad because we can't * rely on the integrity of the object's state. */ public void execute() { data.get("data").toString(); } } The code below is nothing special but I am acting on the parameters and state is contained within that class. We still may run into issues with this class but that is an issue with the method and the state of the data, we can address issues in the routine as opposed to not trusting the entire object. Is this some form of idiom? Is this similar to any pattern that you use? public class SemiStatefulOOP { /** * Private class implies that I can access the members of the <code>Data</code> class * within the <code>SemiStatefulOOP</code> class and I can also access * the getData method from some other class. * * @see Test1 * */ class Data { protected int counter = 0; public int getData() { return counter; } public String toString() { return Integer.toString(counter); } } /** * Act on the data class. */ public void execute(final Data data) { data.counter++; } /** * Act on the data class. */ public void updateStateWithCallToService(final Data data) { data.counter++; } /** * Similar to CLOS (Common Lisp Object System) make instance. */ public Data makeInstance() { return new Data(); } } // End of Class // Issues with the code above: I wanted to declare the Data class private, but then I can't really reference it outside of the class: I can't override the SemiStateful class and access the private members. Usage: final SemiStatefulOOP someObject = new SemiStatefulOOP(); final SemiStatefulOOP.Data data = someObject.makeInstance(); someObject.execute(data); someObject.updateStateWithCallToService(data);

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• Derived template override return type of member function C++

  - by Ruud v A

  I am writing matrix classes. Take a look at this definition: template <typename T, unsigned int dimension_x, unsigned int dimension_y> class generic_matrix { ... generic_matrix<T, dimension_x - 1, dimension_y - 1> minor(unsigned int x, unsigned int y) const { ... } ... } template <typename T, unsigned int dimension> class generic_square_matrix : public generic_matrix<T, dimension, dimension> { ... generic_square_matrix(const generic_matrix<T, dimension, dimension>& other) { ... } ... void foo(); } The generic_square_matrix class provides additional functions like matrix multiplication. Doing this is no problem: generic_square_matrix<T, 4> m = generic_matrix<T, 4, 4>(); It is possible to assign any square matrix to M, even though the type is not generic_square_matrix, due to the constructor. This is possible because the data does not change across children, only the supported functions. This is also possible: generic_square_matrix<T, 4> m = generic_square_matrix<T, 5>().minor(1,1); Same conversion applies here. But now comes the problem: generic_square_matrix<T, 4>().minor(1,1).foo(); //problem, foo is not in generic_matrix<T, 3, 3> To solve this I would like generic_square_matrix::minor to return a generic_square_matrix instead of a generic_matrix. The only possible way to do this, I think is to use template specialisation. But since a specialisation is basically treated like a separate class, I have to redefine all functions. I cannot call the function of the non-specialised class as you would do with a derived class, so I have to copy the entire function. This is not a very nice generic-programming solution, and a lot of work. C++ almost has a solution for my problem: a virtual function of a derived class, can return a pointer or reference to a different class than the base class returns, if this class is derived from the class that the base class returns. generic_square_matrix is derived from generic_matrix, but the function does not return a pointer nor reference, so this doesn't apply here. Is there a solution to this problem (possibly involving an entirely other structure; my only requirements are that the dimensions are a template parameter and that square matrices can have additional functionality). Thanks in advance, Ruud

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• What's the purpose of arrays starting with nonzero index?

  - by helios35

  I tried to find answers, but all I got was answers on how to realize arrays starting with nonzero indexes. Some languages, such as pascal, provide this by default, e.g., you can create an array such as var foobar: array[1..10] of string; I've always been wondering: Why would you want to have the array index not to start with 0? I guess it may be more familiar for beginners to have arrays starting with 1 and the last index being the size of the array, but on a long-term basis, programmers should get used to values starting with 0. Another purpose I could think of: In some cases, the index could actually represent something thats contained in the respective array-entry. e.g., you want to get all capital letters in an array, it may be handy to have an index being the ASCII-Code of the respective letter. But its pretty easy just to subtract a constant value. In this example, you could (in C) simply do something like this do get all capital letters and access the letter with ascii-code 67: #define ASCII_SHIFT 65 main() { int capital_letters[26]; int i; for (i=0; i<26; i++){ capital_letters[i] = i+ASCII_SHIFT; } printf("%c\n", capital_letters[67-ASCII_SHIFT]); } Also, I think you should use hash tables if you want to access entries by some sort of key. Someone might retort: Why should the index always start with 0? Well, it's a hell of a lot simpler this way. You'll be faster when you just have to type one index when declaring an array. Also, you can always be sure that the first entry is array[0] and the last one is array[length_of_array-1]. It is also common that other data structures start with 0. e.g., if you read a binary file, you start with the 0th byte, not the first. Now, why do some programming languages have this "feature" and why do some people ask how to achieve this in languages such as C/C++?, is there any situation where an array starting with a nonzero index is way more useful, or even, something simply cannot be done with an array starting at 0?

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• Is it bad practice to apply class-based design to JavaScript programs?

  - by helixed

  JavaScript is a prototyped-based language, and yet it has the ability to mimic some of the features of class-based object-oriented languages. For example, JavaScript does not have a concept of public and private members, but through the magic of closures, it's still possible to provide the same functionality. Similarly, method overloading, interfaces, namespaces and abstract classes can all be added in one way or another. Lately, as I've been programming in JavaScript, I've felt like I'm trying to turn it into a class-based language instead of using it in the way it's meant to be used. It seems like I'm trying to force the language to conform to what I'm used to. The following is some JavaScript code I've written recently. It's purpose is to abstract away some of the effort involved in drawing to the HTML5 canvas element. /* Defines the Drawing namespace. */ var Drawing = {}; /* Abstract base which represents an element to be drawn on the screen. @param The graphical context in which this Node is drawn. @param position The position of the center of this Node. */ Drawing.Node = function(context, position) { return { /* The method which performs the actual drawing code for this Node. This method must be overridden in any subclasses of Node. */ draw: function() { throw Exception.MethodNotOverridden; }, /* Returns the graphical context for this Node. @return The graphical context for this Node. */ getContext: function() { return context; }, /* Returns the position of this Node. @return The position of this Node. */ getPosition: function() { return position; }, /* Sets the position of this Node. @param thePosition The position of this Node. */ setPosition: function(thePosition) { position = thePosition; } }; } /* Define the shape namespace. */ var Shape = {}; /* A circle shape implementation of Drawing.Node. @param context The graphical context in which this Circle is drawn. @param position The center of this Circle. @param radius The radius of this circle. @praram color The color of this circle. */ Shape.Circle = function(context, position, radius, color) { //check the parameters if (radius < 0) throw Exception.InvalidArgument; var node = Drawing.Node(context, position); //overload the node drawing method node.draw = function() { var context = this.getContext(); var position = this.getPosition(); context.fillStyle = color; context.beginPath(); context.arc(position.x, position.y, radius, 0, Math.PI*2, true); context.closePath(); context.fill(); } /* Returns the radius of this Circle. @return The radius of this Circle. */ node.getRadius = function() { return radius; }; /* Sets the radius of this Circle. @param theRadius The new radius of this circle. */ node.setRadius = function(theRadius) { radius = theRadius; }; /* Returns the color of this Circle. @return The color of this Circle. */ node.getColor = function() { return color; }; /* Sets the color of this Circle. @param theColor The new color of this Circle. */ node.setColor = function(theColor) { color = theColor; }; //return the node return node; }; The code works exactly like it should for a user of Shape.Circle, but it feels like it's held together with Duct Tape. Can somebody provide some insight on this?

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• Microsoft F#

  - by Aamir Hasan

  F# brings you type safe, succinct, efficient and expressive functional programming language on the .NET platform. It is a simple and pragmatic language, and has particular strengths in data-oriented programming, parallel I/O programming, parallel CPU programming, scripting and algorithmic development. F# cannot solve any problem C# could. F# is a functional language, statically typed. F# is a functional language that supports O-O-Programming References:http://msdn.microsoft.com/en-us/fsharp/cc835246.aspx http://research.microsoft.com/en-us/um/cambridge/projects/fsharp/

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• What are good places to get programming online certifications?

  - by Oscar Mederos

  I was reading Am I unhireable? and one of the suggestions @JohnFx gave was getting a few certifications. What is a good place to get online developer certifications? Please, provide info about the site if you used it. I already have some certs in ExpertRating site. Note: It could be certifications about programming in general (methodologies -XP, Scrum, etc-, Modeling, Design Patterns, Architecture, Refactoring, etc.)

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• What are the ways to start making actual/real-world programs using Java/C++ to excel my Programming Skills?

  - by Umer Hassan

  The programming that we learn at university is not that vast, like those are really small exercises to build our logic, but everyone knows that this will not be the scenario when I'll get out in the market as a professional programmer, I really want to make real life programs which would actual make some impacts and will be useful. Tell me in the light of your experience that how should I start making those programs and polish my self as a professional programmer, if there are any sources available for it then kindly also recommend me those.

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• How to apply Data Oriented Design with Object Oriented Programming?

  - by Pombal

  I've read lots of articles about Data Oriented Design (DOD) and I understand it but I can't design an Object Oriented Programming (OOP) system with DOD in mind, I think my OOP education is blocking me. How should I think to mix the two? The objective is to have a nice OOP interface while using DOD behind the scenes. I saw this too but didn't help much: http://stackoverflow.com/questions/3872354/how-to-apply-dop-and-keep-a-nice-user-interface

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• Beginning programming for real clients, what copyright should I put in the code?

  - by Igor Marvinsky

  Hello. So far, I've been writing projects for my friends and friends of my friends, which required no legal stuff. Now I've moved on to freelance programming on websites like vworker.com and I'm wondering what should I put in the comments on top of the code. I'm not doing big, serious serious projects, just frontends and scrapers/bots for what I gather is personal use. Would my usual // Written by Igor Marvinsky, 2011 be enough?

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