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• When to define SDD operations System->Actor?

  - by devoured elysium

  I am having some trouble understanding how to make SDDs, as I don't fully grasp why in some cases one should define operations for System - Actor and in others don't. Here is an example: 1) The User tells the System that wants to buy some tickets, stating his client number. 2) The System confirms that the given client number is valid. 3) The User tells the System the movie that wants to see. 4) The System shows the set of available sessions and seats for that movie. 5) The System asks the user which session/seat he wants. 6) The user tells the System the chosen session/seat. This would be converted to: a) -----> tellClientNumber(clientNumber) b) <----- validClientNumber c) -----> tellMovieToSee(movie) d) <----- showsAvailableSeatsHours e) -----> tellSystemChosenSessionSeat(session, seat) I know that when we are dealing with SDD's we are still far away from coding. But I can't help trying to imagine how it how it would have been had I to convert it right away to code: I can understand 1) and 2). It's like if it was a C#/Java method with the following signature: boolean tellClientNumber(clientNumber) so I put both on the SDD. Then, we have the pair 3) 4). I can imagine that as something as: SomeDataStructureThatHoldsAvailableSessionsSeats tellSystemMovieToSee(movie) Now, the problem: From what I've come to understand, my lecturer says that we shouldn't make an operation on the SDD for 5) as we should only show operations from the Actor to the System and when the System is either presenting us data (as in c)) or validating sent data (such as in b)). I find this odd, as if I try to imagine this like a DOS app where you have to put your input sequencially, it makes sense to make an arrow even for 5). Why is this wrong? How should I try to visualize this? Thanks

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• Why should I abstract my data layer?

  - by Gazillion

  OOP principles were difficult for me to grasp because for some reason I could never apply them to web development. As I developed more and more projects I started understanding how some parts of my code could use certain design patterns to make them easier to read, reuse, and maintain so I started to use it more and more. The one thing I still can't quite comprehend is why I should abstract my data layer. Basically if I need to print a list of items stored in my DB to the browser I do something along the lines of: $sql = 'SELECT * FROM table WHERE type = "type1"';' $result = mysql_query($sql); while($row = mysql_fetch_assoc($result)) { echo '<li>'.$row['name'].'</li>'; } I'm reading all these How-Tos or articles preaching about the greatness of PDO but I don't understand why. I don't seem to be saving any LoCs and I don't see how it would be more reusable because all the functions that I call above just seem to be encapsulated in a class but do the exact same thing. The only advantage I'm seeing to PDO are prepared statements. I'm not saying data abstraction is a bad thing, I'm asking these questions because I'm trying to design my current classes correctly and they need to connect to a DB so I figured I'd do this the right way. Maybe I'm just reading bad articles on the subject :) I would really appreciate any advice, links, or concrete real-life examples on the subject!

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• C -- Basic Struct questions

  - by Ryan Yu

  So I'm trying to learn C right now, and I have some basic struct questions I'd like to clear up: Basically, everything centers around this snippet of code: #include <stdio.h> #include <stdlib.h> #define MAX_NAME_LEN 127 typedef struct { char name[MAX_NAME_LEN + 1]; unsigned long sid; } Student; /* return the name of student s */ const char* getName (const Student* s) { // the parameter 's' is a pointer to a Student struct return s->name; // returns the 'name' member of a Student struct } /* set the name of student s If name is too long, cut off characters after the maximum number of characters allowed. */ void setName(Student* s, const char* name) { // 's' is a pointer to a Student struct | 'name' is a pointer to the first element of a char array (repres. a string) s->name = name; } /* return the SID of student s */ unsigned long getStudentID(const Student* s) { // 's' is a pointer to a Student struct return s->sid; } /* set the SID of student s */ void setStudentID(Student* s, unsigned long sid) { // 's' is a pointer to a Student struct | 'sid' is a 'long' representing the desired SID s->sid = sid; } I've commented up the code in an attempt to solidify my understanding of pointers; I hope they're all accurate. So anyway, I have a feeling that setName and setStudentID aren't correct, but I'm not exactly sure why. Can someone explain? Thanks!

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• C++ union data-structure, easy acccess of bits within a DWORD

  - by TK

  Im running through a set of DirectX tutorials online and I have the following structure: struct CUSTOMVERTEX { FLOAT x, y, z, rhw; // from the D3DFVF_XYZRHW flag DWORD color; // from the D3DFVF_DIFFUSE flag } My basic understanding of directX leads me to thing tha color is made up of 8-bit alpha, red, green and blue channels. I am attempting to get east access to these channels. Rather than write the following code numerous times (within the CUSTOMVERTEX structure): public: int red() { return (color & 0x00FF0000) >> 16; } I could write a more elegant somution with a combination of a union and a structure e.g. struct CUSTOMVERTEX { FLOAT x, y, z, rhw; // from the D3DFVF_XYZRHW flag #pragma pack(2) union { DWORD color; // from the D3DFVF_DIFFUSE flag struct { char a; char r; char g; char b; }; }; } However this does not appear to function as expected, the values in r, g, & b almost appear the reverse of whats in color e.g. if color is 0x12345678 a = 0x78, r = 0x56. Is this an endieness issue? Also what other problems could I be expecting from this solution? e.g. overflow from the color members? I guess what Im asking is ... is there a better way to do this?!

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• Why does Python's 'for ... in' work differently on a list of values vs. a list of dictionaries?

  - by Code Duck

  I'm wondering about some details of how for ... in works in Python. My understanding is for var in iterable on each iteration creates a variable, var, bound to the current value of iterable. So, if you do for c in cows; c = cows[whatever], but changing c within the loop does not affect the original value. However, it seems to work differently if you're assigning a value to a dictionary key. cows=[0,1,2,3,4,5] for c in cows: c+=2 #cows is now the same - [0,1,2,3,4,5] cows=[{'cow':0},{'cow':1},{'cow':2},{'cow':3},{'cow':4},{'cow':5}] for c in cows: c['cow']+=2 # cows is now [{'cow': 2}, {'cow': 3}, {'cow': 4}, {'cow': 5}, {'cow': 6}, {'cow': 7} #so, it's changed the original, unlike the previous example I see one can use enumerate to make the first example work, too, but that's a different story, I guess. cows=[0,1,2,3,4,5] for i,c in enumerate(cows): cows[i]+=1 # cows is now [1, 2, 3, 4, 5, 6] Why does it affect the original list values in the second example but not the first?

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• c++ and visual studio 08, how to develop the following web extracting application. folloow up of las

  - by user287745

  the purpose is to use c++ in a useful way. i have just started programming and have made a few small applications in c and c#. my understanding is that programming for web and thing related to web is now a days a very easy task. please note this is for personnel learning not for rent a coder or any money making. an application which can run on any windows platform even win98. the application should start automatically at a scheduled time and do the following. connect to a site which displays stock prices summary (high low current open ). captures the data (excluding the other things in the site) and saves it to disk ( a sql database) please note:- internet connection is assumed to be there always. do not want to know how to make database schema or database. the stock exchange has no law prohibiting the use of the data provided on its site, but i do not want to mention the name in case i am wrong, but its for personnel private use only. the data of summary of pricing is arranged in a table such that when copied pasted to ms excel it automatically forms a table. guidance needed thank u.

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• Java's Swing Threading

  - by nevets1219

  My understanding is that if I start up another thread to perform some actions, I would need to SwingUtilities.invokeAndWait or SwingUtilities.invokeLater to update the GUI while I'm in said thread. Please correct me if I'm wrong. What I'm trying to accomplish is relatively straightforward: when the user clicks submit, I want to (before performing any actions) disable the submit button, perform the action, and at the end of the action re-enable the button. My method to perform the action updates the GUI directly (displays results) when it gets the results back. This action basically queries a server and gets some results back. What I have so far is: boolean isRunning = false; synchronized handleButtonClick() { if ( isRunning == false ) { button.setEnabled( false ); isRunning = true; doAction(); } } doAction() { new Thread() { try { doAction(); // Concern A } catch ( ... ) { displayStackTrace( ... ); // Concern B } finally { SwingUtilities.invokeLater ( /* simple Runnable to enable button */ ); isRunning = false; } } } For both of my concerns above, do I would have to use SwingUtilities.invokeAndWait since they both will update the GUI? All GUI updates revolve around updating JTextPane. Do I need to in my thread check if I'm on EDT and if so I can call my code (regardless of whether it updates the GUI or not) and NOT use SwingUtilities.invokeAndWait?

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• How do you convert an unsigned int[16] of hexidecimal to an unsigned char array without losing any information?

  - by user1068636

  I have a unsigned int[16] array that when printed out looks like this: 4418703544ED3F688AC208F53343AA59 The code used to print it out is this: for (i = 0; i < 16; i++) printf("%X", CipherBlock[i] / 16), printf("%X",CipherBlock[i] % 16); printf("\n"); I need to pass this unsigned int array "CipherBlock" into a decrypt() method that only takes unsigned char *. How do correctly memcpy everything from the "CipherBlock" array into an unsigned char array without losing information? My understanding is an unsigned int is 4 bytes and unsigned char 1 byte. Since "CipherBlock" is 16 unsigned integers, the total size in bytes = 16 * 4 = 64 bytes. Does this mean my unsigned char[] array needs to be 64 in length? If so, would the following work? unsigned char arr[64] = { '\0' }; memcpy(arr,CipherBlock,64); This does not seem to work. For some reason it only copies the the first byte of "CipherBlock" into "arr". The rest of "arr" is '\0' thereafter.

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• StructureMap Configuration Per Thread/Request for the Full Dependency Chain

  - by Phil Sandler

  I've been using Structuremap for a few months now, and it has worked great on some smaller (green field) projects. Most of the configurations I have had to set up involve a single implementation per interface. In the cases where I needed to choose a specific implementation at runtime, I created a factory class that used ObjectFactory.GetNamedInstance<(). In the smaller projects, there were few enough of these cases where I was comfortable with the references to ObjectFactory. My understanding is that you want to limit these references as much as possible, and ideally only reference the ObjectFactory once. I am working to refactor a larger codebase to use IOC/StructureMap, and am finding that I may need many of these factory classes with ObjectFactory references to get what I need. Essentially, I am creating a "root service" with the ObjectFactory, so that everything in the dependency chain is managed by the container. The root service is created by name (i.e. "BuildCar", "BuildTruck"), and the services needed deeper in the dependency chain could also be constructed using the same name--so the "IAttachWheels" service could vary based on whether a car or truck is being built. Since the class that depends on IAttachWheels is the same in both configurations, I don't think I can use ConstructedBy in the registry to choose the implementation. Also, to be clear, the IAttachWheels implementations need to be managed by the container as well, because the dependency chain runs fairly deep. I looked briefly at Profiles as an option, but read (here on StackOverflow) that changing profiles essentially changes implementations for all threads. Is there a feature that is similar to profiles that is thread/request specific? Is the factory class that references ObjectFactory approach the right way to go? Any thoughts would be appreciated.

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• With ASP.NET MVC, what is the preferred way to Ajaxify a simple form?

  - by Swoop

  I am trying to add a simple comments/message box to a web page. When the user enters the comment and hits submit, I would like to save this message to the database and add the comment to the list displayed on the page, without refreshing the entire page. However, I am not sure of the best way to do that these days. I am using ASP.NET MVC 2. I have been trying to read up on using JQuery for this type of functionality, but I am having problems getting a full picture of the correct approach that isn't also out of date (i.e. it is using an preview version of MVC 1 or older version of JQuery). I can either find snippets of different pieces without the information of how they work together, or the information appears to be quite dated and no longer valid. Can someone point me in the right direction for something like this? Ideally, I am looking for a simple example of the JQuery code, a snippet of any key differences in an HTML form from a normal post method, and the basic method used in the MVC Controller. I need something to help the lightbulb of understanding to turn on. :) Any help would be greatly appreciated!!

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• WindowsFormsApplicationBase SplashScreen makes login form ignore keypresses until I click on it - how to debug?

  - by Tom Bushell

  My WinForms app has a simple modal login form, invoked at startup via ShowDialog(). When I run from inside Visual Studio, everything works fine. I can just type in my User ID, hit the Enter key, and get logged in. But when I run a release build directly, everything looks normal (the login form is active, there's a blinking cursor in the User ID MaskedEditBox), but all keypresses are ignored until I click somewhere on the login form. Very annoying if you are used to doing everything from the keyboard. I've tried to trace through the event handlers, and to set the focus directly with code, to no avail. Any suggestions how to debug this (outside of Visual Studio), or failing that - a possible workaround? Edit Here's the calling code, in my Main Form: private void OfeMainForm_Shown(object sender, EventArgs e) { OperatorLogon(); } private void OperatorLogon() { // Modal dialogs should be in a "using" block for proper disposal using (var logonForm = new C21CfrLogOnForm()) { var dr = logonForm.ShowDialog(this); if (dr == DialogResult.OK) SaveOperatorId(logonForm.OperatorId); else Application.Exit(); } } Edit 2 Didn't think this was relevant, but I'm using Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase for it's splash screen and SingleInstanceController support. I just commented out the splash screen code, and the problem has disappeared. So that's opened up a whole new line of inquiry... Edit 3 Changed title to reflect better understanding of the problem

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• The Purpose of a Service Layer and ASP.NET MVC 2

  - by user332022

  In an effort to understand MVC 2 and attempt to get my company to adopt it as a viable platform for future development, I have been doing a lot of reading lately. Having worked with ASP.NET pretty exclusively for the past few years, I had some catching up to do. Currently, I understand the repository pattern, models, controllers, data annotations, etc. But there is one thing that is keeping me from completely understanding enough to start work on a reference application. The first is the Service Layer Pattern. I have read many blog posts and questions here on Stack Overflow, but I still don't completely understand the purpose of this pattern. I watched the entire video series at MVCCentral on the Golf Tracker Application and also looked at the demo code he posted and it looks to me like the service layer is just another wrapper around the repository pattern that doesn't perform any work at all. I also read this post: http://www.asp.net/Learn/mvc/tutorial-38-cs.aspx and it seemed to somewhat answer my question, however, if you are using data annotations to perform your validation, this seems unnecessary. I have looked for demonstrations, posts, etc. but I can't seem to find anything that simply explains the pattern and gives me compelling evidence to use it. Can someone please provide me with a 2nd grade (ok, maybe 5th grade) reason to use this pattern, what I would lose if I don't, and what I gain if I do?a

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• R Tree 50,000 foot overview?

  - by roufamatic

  I'm working on a school project that involves taking a lat/long point and finding the top five closest points in a known list of places. The list is to be stored in memory, with the caveat that we must choose an "appropriate data structure" -- that is, we cannot simply store all the places in an array and compare distances one-by-one in a linear fashion. The teacher suggested grouping the place data by US State to prevent calculating the distance for places that are obviously too far away. I think I can do better. From my research online it seems like an R-Tree or one of its variants might be a neat solution. Unfortunately, that sentence is as far as I've gotten with understanding the actual technique, as the literature is simply too dense for my non-academic head. Can somebody give me a really high overview of what the process is for populating an R-Tree with lat/long data, and then traversing the tree to find those 5 nearest neighbors of a given point? Additionally the project is in C, and I don't have to reinvent the wheel on this, so if you've used an existing open source C implementation of an R Tree I'd be interested in your experiences.

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• trouble with state monad composition

  - by user1308560

  I was trying out the example given at http://www.haskell.org/haskellwiki/State_Monad#Complete_and_Concrete_Example_1 How this makes the solution composible is beyond my understanding. Here is what I tried but I get compile errors as follows: Couldn't match expected type `GameValue -> StateT GameState Data.Functor.Identity.Identity b0' with actual type `State GameState GameValue' In the second argument of `(>>=)', namely `g2' In the expression: g1 >>= g2 In an equation for `g3': g3 = g1 >>= g2 Failed, modules loaded: none. Here is the code: See the end lines module StateGame where import Control.Monad.State type GameValue = Int type GameState = (Bool, Int) -- suppose I want to play one game after the other g1 = playGame "abcaaacbbcabbab" g2 = playGame "abcaaacbbcabb" g3 = g1 >>= g2 m2 = print $ evalState g3 startState playGame :: String -> State GameState GameValue playGame [] = do (_, score) <- get return score playGame (x:xs) = do (on, score) <- get case x of 'a' | on -> put (on, score + 1) 'b' | on -> put (on, score - 1) 'c' -> put (not on, score) _ -> put (on, score) playGame xs startState = (False, 0) main str = print $ evalState (playGame str) startState

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• Using delegate Types vs methods

  - by Grant Sutcliffe

  I see increasing use of the delegate types offered in the System namespace (Action; Predicate etc). As these are delegates, my understanding is that they should be used where we have traditionally used delegates in the past (asynchronous calls; starting threads, event handling etc). Is it just preference or is it considered practice to use these delegate types in scenarios such as the below; rather than using calls to methods we have declared (or anonymous methods): public void MyMethod { Action<string> action = delegate(string userName { try { XmlDocument profile = DataHelper.GetProfile(userName); UpdateMember(profile); } catch (Exception exception) { if (_log.IsErrorEnabled) _log.ErrorFormat(exception.Message); throw (exception); } }; GetUsers().ForEach(action); } At first, I found the code less intuitive to follow than using declared or anonymous methods. I am starting to code this way, and wonder what the view are in this regard. The example above is all within a method. Is this delegate overuse.

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• Linear Interpolation. How to implement this algorithm in C ? (Python version is given)

  - by psihodelia

  There exists one very good linear interpolation method. It performs linear interpolation requiring at most one multiply per output sample. I found its description in a third edition of Understanding DSP by Lyons. This method involves a special hold buffer. Given a number of samples to be inserted between any two input samples, it produces output points using linear interpolation. Here, I have rewritten this algorithm using Python: temp1, temp2 = 0, 0 iL = 1.0 / L for i in x: hold = [i-temp1] * L temp1 = i for j in hold: temp2 += j y.append(temp2 *iL) where x contains input samples, L is a number of points to be inserted, y will contain output samples. My question is how to implement such algorithm in ANSI C in a most effective way, e.g. is it possible to avoid the second loop? NOTE: presented Python code is just to understand how this algorithm works. UPDATE: here is an example how it works in Python: x=[] y=[] hold=[] num_points=20 points_inbetween = 2 temp1,temp2=0,0 for i in range(num_points): x.append( sin(i*2.0*pi * 0.1) ) L = points_inbetween iL = 1.0/L for i in x: hold = [i-temp1] * L temp1 = i for j in hold: temp2 += j y.append(temp2 * iL) Let's say x=[.... 10, 20, 30 ....]. Then, if L=1, it will produce [... 10, 15, 20, 25, 30 ...]

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• What's the *right* way to handle a POST in FP?

  - by Malvolio

  I'm just getting started with FP and I'm using Scala, which may not be the best way, since I can always fall back to an imperative style if the going gets tough. I'd just rather not. I've got a very specific question that points to a broader lacuna in my understanding of FP. When a web application is processing a GET request, the user wants information that already exists on the web-site. The application only has to process and format the data in some way. The FB way is clear. When a web application is processing a POST request, the user wants change the information held on the site. True, the information is not typically held in application variables, it's in a database or a flat-file, but still, I get the feeling I'm not grokking FP properly. Is there a pattern for handling updates to static data in an FP language? My vague picture of this is that the application is handed the request and the then-current site state. The application does its thing and returns the new site-state. If the current site-state hasn't changed since the application started, the new state becomes the current state and the reply is sent back to the browser (this is my dim image of Clojure's style); if the current state has been changed (by another thread, well, something else happens ...

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• Repository Pattern Standardization of methods

  - by Nix

  All I am trying to find out the correct definition of the repository pattern. My original understanding was this (extremely dubmed down) Separate your Business Objects from your Data Objects Standardize access methods in data access layer. I have really seen 2 different implementations. Implementation 1 : public Interface IRepository<T>{ List<T> GetAll(); void Create(T p); void Update(T p); } public interface IProductRepository: IRepository<Product> { //Extension methods if needed List<Product> GetProductsByCustomerID(); } Implementation 2 : public interface IProductRepository { List<Product> GetAllProducts(); void CreateProduct(Product p); void UpdateProduct(Product p); List<Product> GetProductsByCustomerID(); } Notice the first is generic Get/Update/GetAll, etc, the second is more of what I would define "DAO" like. Both share an extraction from your data entities. Which I like, but i can do the same with a simple DAO. However the second piece standardize access operations I see value in, if you implement this enterprise wide people would easily know the set of access methods for your repository. Am I wrong to assume that the standardization of access to data is an integral piece of this pattern ? Rhino has a good article on implementation 1, and of course MS has a vague definition and an example of implementation 2 is here.

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• Trouble with go tour crawler exercise

  - by David Mason

  I'm going through the go tour and I feel like I have a pretty good understanding of the language except for concurrency. On slide 71 there is an exercise that asks the reader to parallelize a web crawler (and to make it not cover repeats but I haven't gotten there yet.) Here is what I have so far: func Crawl(url string, depth int, fetcher Fetcher, ch chan string) { if depth <= 0 { return } body, urls, err := fetcher.Fetch(url) if err != nil { ch <- fmt.Sprintln(err) return } ch <- fmt.Sprintf("found: %s %q\n", url, body) for _, u := range urls { go Crawl(u, depth-1, fetcher, ch) } } func main() { ch := make(chan string, 100) go Crawl("http://golang.org/", 4, fetcher, ch) for i := range ch { fmt.Println(i) } } The issue I have is where to put the close(ch) call. If I put a defer close(ch) somewhere in the Crawl method, then I end up writing to a closed channel in one of the spawned goroutines, since the method will finish execution before the spawned goroutines do. If I omit the call to close(ch), as is shown in my example code, the program deadlocks after all the goroutines finish executing but the main thread is still waiting on the channel in the for loop since the channel was never closed.

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• Acessing a wordpress database from an iPhone App.

  - by Code

  Hi guys, I've been asked to create an app that will get data back from a database where the CMS will be Wordpress. I've never used a CMS so I'm trying to get a (overview)picture in my head of how it could all work and what each of the components would be. And what a CMS actually brings to the party. Creating the app itself is pretty clear. I've done a few already. I've made a database before and shouldnt cause a problem. But what is going to be in the middle between the app and the database? Part A: I'm guessing iphone apps typically would call some php file that's hosted on the server? The php then would make a call to the database and return the data somehow, maybe as xml. But this is really basic and wouldnt require a CMS. Just a database and a phpfile, or am I wrong? Part B: If i wanted to run a check on the database every minute to see if any of the data in database was no longer valid and remove it if needed, that would require somekind of program running on the server. So that program would be Wordpress, since it is managing the content, so a content management system is actually needed and is for these kind of taskes. Am i understanding the role of CMS? Many Thanks, -Code

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• calling constructor of the class in the destructor of the same class

  - by dicaprio

  Experts !! I know this question is one of the lousy one , but still I dared to open my mind , hoping I would learn from all. I was trying some examples as part of my routine and did this horrible thing, I called the constructor of the class from destructor of the same class. I don't really know if this is ever required in real programming , I cant think of any real time scenarios where we really need to call functions/CTOR in our destructor. Usually , destructor is meant for cleaning up. If my understanding is correct, why the compiler doesn't complain ? Is this because it is valid for some good reasons ? If so what are they ? I tried on Sun Forte, g++ and VC++ compiler and none of them complain about it. using namespace std; class test{ public: test(){ cout<<"CTOR"<<endl; } ~test() {cout<<"DTOR"<<endl; test(); }};

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• Within a DLL, how is the function table structured?

  - by Willi Ballenthin

  I've been looking into the implementation of a device library that doesn't explicitly support my operating system. In particular, I have a disassembled DLL, and a fair amount of supporting source code. Now, how is the function table/export table structured? My understanding is that the first structure of the .data section is a table of VRAs. Next is a table of strings linked by index to that first address table. This makes sense to me, as a linker could translate between symbols and addresses. How do functions referenced by ordinals fit into this picture? How does one know which function has such and such ordinal number, and how does the linker resolve this? In other words, given that some other DLL imports SOME_LIBRARY_ordinal_7, how does the linker know which function to work with? Thanks, all! edit More information... Im working with the FTDI libraries, and would like to resolve which function is being invoked. In particular, I see something like: extern FTD2XX_Ordinal_28: near how might I go about determining which function is being referenced, and how does the linker do this?

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• efficient thread-safe singleton in C++

  - by user168715

  The usual pattern for a singleton class is something like static Foo &getInst() { static Foo *inst = NULL; if(inst == NULL) inst = new Foo(...); return *inst; } However, it's my understanding that this solution is not thread-safe, since 1) Foo's constructor might be called more than once (which may or may not matter) and 2) inst may not be fully constructed before it is returned to a different thread. One solution is to wrap a mutex around the whole method, but then I'm paying for synchronization overhead long after I actually need it. An alternative is something like static Foo &getInst() { static Foo *inst = NULL; if(inst == NULL) { pthread_mutex_lock(&mutex); if(inst == NULL) inst = new Foo(...); pthread_mutex_unlock(&mutex); } return *inst; } Is this the right way to do it, or are there any pitfalls I should be aware of? For instance, are there any static initialization order problems that might occur, i.e. is inst always guaranteed to be NULL the first time getInst is called?

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• What do you call a set of Javascript closures that share a common context?

  - by Ed Stauff

  I've been trying to learn closures (in Javascript), which kind of hurts my brain after way too many years with C# and C++. I think I now have a basic understanding, but one thing bothers me: I've visited lots of websites in this Quest for Knowledge, and nowhere have I seen a word (or even a simple two-word phrase) that means "a set of Javascript closures that share a common execution context". For example: function CreateThingy (name, initialValue) { var myName = name; var myValue = initialValue; var retObj = new Object; retObj.getName = function() { return myName; } retObj.getValue = function() { return myValue; } retObj.setValue = function(newValue) { myValue = newValue; } return retObj; }; From what I've read, this seems to be one common way of implementing data hiding. The value returned by CreateThingy is, of course, an object, but what would you call the set of functions which are properties of that object? Each one is a closure, but I'd like a name I can used to describe (and think about) all of them together as one conceptual entity, and I'd rather use a commonly accepted name than make one up. Thanks! -- Ed

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• Wicket: Where to add components? Constructor? Or onBeforeRender?

  - by gmallett

  I'm a Wicket newb. This may just be my ignorance of the Wicket lifecycle so please enlighten me! My understanding is that Wicket WebPage objects are instantiated once and then serialized. This has led to a point of confusion for me, see below. Currently I have a template class which I intend to subclass. I followed the example in the Wicket docs demonstrating how to override the template's behavior in the subclass: protected void onBeforeRender() { add(new Label("title", getTitle())); super.onBeforeRender(); } protected String getTitle() { return "template"; } Subclass: protected String getTitle() { return "Home"; } This works very well. What's not clear to me are the "best practices" for this. It seems like onBeforeRender() is called on every request for the page, no? This seems like there would be substantially more processing done on a page if everything is in onBeforeRender(). I could easily follow the example of the other Wicket examples and add some components in the constructor that I do not want to override, but then I've divided by component logic into two places, something I'm hesitant to do. If I add a component that I intend to be in all subclasses, should I add it to the constructor or onBeforeRender()?

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