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  • Interpreter in C++: Function table storage problem

    - by sub
    In my interpreter I have built-in functions available in the language like print exit input, etc. These functions can obviously be accessed from inside the language. The interpreter then looks for the corresponding function with the right name in a vector and calls it via a pointer stored with its name. So I gather all these functions in files like io.cpp, string.cpp, arithmetic.cpp. But I have to add every function to the function list in the interpreter in order for it to be found. So in these function files I have things like: void print( arg ) { cout << arg.ToString; } I'd add this print function to the interpreter function list with: interpreter.AddFunc( "print", print ); But where should I call the interpreter.AddFunc? I can't just put it there below the print function as it has to be in a function according to the C++ syntax. Where and how should all the functions be added to the list?

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  • design decision between array or object save in database

    - by justjoe
    i code some configuration setting. And need those values to be load, everytime my webapp start. yes, it's somekind autoload setting. But, right now, i have to choose between save it as object or array. is there any different between them when we save them in database ? which one is faster or maintainable or other pro and cons thanks

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  • What is the best practice for accessing Model using MVVM pattern

    - by Dzenand
    I have a database that communicates with webservices with my Model (own thread) and exposes Data Objects. My UI application consists of different Views and ViewModels and Custom Controls. I'm using ServiceProvider (IServiceProvider) to access the Model and route the events to the UI thread. Communication between the ViewModels is handeled by a Messenger. Is this way to go? I was also wondering what is the best way to strucutre the DataObjects At the moment i have the DataObjects that have a hierarchy structure but does not support INotifyProperty though the children list are of type of ObservableCollection. I have no possiblity to implement notifypropertychange on the properties. I was wondering the best way of making them MVVM friendly. Implementing a partial class and adding all the properties or commands that are necessary or wrapping all the DataObjects and keep the Model list and MVVM list in sync. All thoughts and ideas are appreciated.

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  • Does writing program using global variables is safer?

    - by ZoZo123
    I was reading about buffer, stack and heap overflows. I read this post as well. my question is like that: if I use only global variables in my code, can I say it prevents all the exploits of overflow? let's say I have this buffers in code declared in the global scope: char buf1[10]; char buf2[100]; If I send buf1 as the buffer to recv(int s, char *buf, int len,int flags); I will overwrite the data segment and may ruin the buf2 content, right? Would I be able to run a code from it because as I know it is not a code segment and data segment is not executable. Can we conclude that using Globals is the safest way?

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  • How should I handle expected errors? eg. "username already exists"

    - by Pheter
    I am struggling to understand how I should design the error handling parts of my code. I recently asked a similar question about how I should go about returning server error codes to the user, eg. 404 errors. I learnt that I should handle the error from within the current part of the application; seem's simple enough. However, what should I do when I can't handle the error from the current link in the chain? For example, I may have a class that is used to manage authentication. One of it's methods could be createUser($username, $password). Within that function, I need to determine if the username already exists. If this is true, how should I alert the calling code about this? Returning null instead of a user object is one way. But how do I then know what caused the error? How should I handle errors in such a way that calling code can easily find out what caused the error? Is there a design pattern commonly used for this kind of situation?

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  • Keeping Computer Science Writing Accessible and Eloquent

    - by Federer
    This question is particularly aimed at descriptions and explanations of what is happening in a computer program, as well as any general advice or approaches for undertaking technical reports in Computer Science at both undergraduate and graduate levels. You see, I am having particular difficulty in the best way to explain what is happening. As in, given any given program from a multi-agent system to a standard webservice, the best and most eloquent way to say exactly what is going on, the logic behind it and it's respective justifications. Should I avoid saying class names? Avoid specifying methods? Keep referring to class variables and any particular references? I'm banging my head against the wall at trying to keep a solid technical foundation and making it accessible to people of all backgrounds. Apologies for the rather vague question. Cheers.

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  • command design pattern usage

    - by sagie
    Hi. I've read 3 descriptions of the command design pattern: wikipedia, dofactory and source making. In all of them, the UML shows a relation between the client to the receiver & the concrete command, but no relation to the invoker. But in all 3 examples the client is the one that initiates the invoker and call its Execute method. I think that should be a relation to the invoker as well. Am I missing somthing in here? Maybe even a basic UML knowladge?

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  • How to face observable object containing an observable field

    - by iseek
    Hello, I need a hint concerning MVC and Observer-Pattern. For example a model contains the classes "Address" and "Person". The Address class contains the fields street:String, zipcode:String, location:String. Whereas the Person class contains the fields name:String, firstName:String, address:Address. My approach so far looks something like this: Both, Address and Person are observable. If one of their setters is being called, I validate whether the current value and new value differ. Only in this case an update event is fired. The event contains the source, the name of the changed field, the old and the new value. The class for the view contains text fields to display and edit the information of a person: name, firstname, street, zipcode, location. It knows the Person model and is an subscribed observer for the person. So it gets the update events from the person object. My questions concerns the address field from type Address in the person class, since an address is observable on its own. If the view gets an update event from person when a new address has been set, I can update all of the address related fields in the view. But what if a field of the address changes? Should the view also register for update events from the address? Any hints about common design approaches would be appreciated. Greetings.

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  • Design pattern: polymorphisim for list of objects

    - by ziang
    Suppose I have a class A, and A1, A2 inherits from A. There are 2 functions: List<A1> getListA1(){...} List<A2> getListA2(){...} Now I want to do something similar to both A1 and A2 in another function public void process(List<A>){...} If I want to pass the instance of either ListA1 or ListA2, of course the types doesn't match because the compiler doesn't allow the coercion from List< A1 to List< A. I can't do something like this: List<A1> listA1 = getListA1(); List<A> newList = (List<A>)listA1; //this is not allowed. So what is the best approach to the process()? Is there any way to do it in a universal way rather than write the similar code to both List and List?

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  • Drupal 6 devel module dd() function not writing to drupal_debug.txt file

    - by Mike Munroe
    I am running a local development Drupal site on a Windows machine. I am trying to use the dd($data, $label = NULL) function from the devel module to help debug. Using this function, should write debug info to a drupal_debug.txt file in the /tmp folder on the machine where the Drupal site is hosted. On my Windows machine, although I am using this function, the drupal_debug.txt file is not getting created anywhere, leading me to believe I am using the function incorrectly. Here is a snippet of how I am using it, <?php $test = "this is my test"; dd($test, $label = NULL); I am looking for an example of the correct syntax for the dd($data, $label = NULL) function. I have the Devel module enabled.

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  • writing something in jList

    - by bigbluedragon
    hey i have another problem. I created jList in my main window and now i want to add something to it. I do it this way... private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) { Dodaj_Przedmiot dodaj_przedmiot = new Dodaj_Przedmiot(null, true); dodaj_przedmiot.setVisible(true); SterowanieBazy instance = SterowanieBazy.getInstance(); Zmienne_pomocnicze zp = new Zmienne_pomocnicze(); instance.dodajPrzedmiot(przedmiot); String przedm[] = instance.zwrocPrzedmioty(); jList1.setListData(przedm); } what i want to write in that list is what i collect from my jDialogForm: dodaj_przedmiot private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) { String sciezka = jTextField1.getText(); if (sciezka.length() > 0) { Zmienne_pomocnicze zp = new Zmienne_pomocnicze(); zp.setPrzechowaj(sciezka); } this.setVisible(false); } and i collect try to copy that date using this class public class Zmienne_pomocnicze { public String n; public int a; public void setPrzechowaj (String neew) { n = neew; } public String getPrzechowaj () { return n; } } i would be grateful for any ideas how to make it works^^

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  • Writing an Eval Procedure in Scheme?

    - by Planeman
    My problem isn't with the built-in eval procedure but how to create a simplistic version of it. Just for starters I would like to be able to take this in '(+ 1 2) and have it evaluate the expression + where the quote usually takes off the evaluation. I have been thinking about this and found a couple things that might be useful: Unquote: , (quasiquote) (apply) My main problem is regaining the value of + as a procedure and not a symbol. Once I get that I think I should just be able to use it with the other contents of the list. Any tips or guidance would be much appreciated.

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  • Should I use a modified singleton design pattern that only allows one reference to its instance?

    - by Graham
    Hi, I have a class that would normally just generate factory objects, however this class should only used once throughout the program in once specifix place. What is the best design pattern to use in this instance? I throught that having a modified singleton design which only allows one reference to instance throughout the program would be the correct way to go. So only the first call to getInstance() returns the factory library. Is this a good or bad idea? Have I missed out another fundermental design pattern for solving this problem? Thanks for your help.

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  • pattern to transfer search model to dao

    - by zeroed
    We have a dao as a project (jar file). Clients use its interfaces and factories to operate with database. Using standard CRUD operations, dao allows you to search an entity by some search criteria. What is the best way to represent this criteria? Is transfer object appropriate pattern in this situation? How should client create SearchModel instance? Please, share. Regards.

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  • How can I get my business objects layer to use the management layer in their methods?

    - by Tom Pickles
    I have a solution in VS2010 with several projects, each making up a layer within my application. I have business entities which are currently objects with no methods, and I have a management layer which references the business entities layer in it's project. I now think I have designed my application poorly and would like to move methods from helper classes (which are in another layer) into methods I'll create within the business entities themselves. For example I have a VirtualMachine object, which uses a helper class to call a Reboot() method on it which passes the request to the management layer. The static manager class talks to an API that reboots the VM. I want to move the Reboot() method into the VirtualMachine object, but I will need to reference the management layer: public void Reboot() { VMManager.Reboot(this.Name); } So if I add a reference to my management project in my entities project, I get the circular dependency error, which is how it should be. How can I sort this situation out? Do I need to an yet another layer between the entity layer and the management layer? Or, should I just forget it and leave it as it is. The application works ok now, but I am concerned my design isn't particularly OOP centric and I would like to correct this.

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  • Have you ever derived a programming solution from nature?

    - by Ryu
    When you step back and look at ... the nature of animals, insects, plants and the problems they have organically solved perhaps even the nature and balance of the universe Have you ever been able to solve a problem by deriving an approach from nature? I've heard of Ant Colony Algorithms being able to optimize supply chain amongst other things. Also Fractal's being the "geometry of nature" have been applied to a wide range of problems. Now that spring is here again and the world is coming back to life I'm wondering if anybody has some experiences they can share. Thanks PS I would recommend watching the "Hunting the Hidden Dimension" Nova episode on fractals.

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  • Guide on writing my first open source software ?

    - by Kim Jong Woo
    Hello Stackoverflow, Since last August 2009, I have been working on project but then decided to release it as an open source project. The purpose of this project is to provide an alternative to existing commercial & expensive solution. So my question is, how can I get started ? The prototype has been ready since May and now being rewritten in Java. Which license type do I need to pursue ? LGPL? MIT? Thank you, John.

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  • ASP.NET MVC Filters: How to set Viewdata for Dropdown based on action paramter

    - by CRice
    Hi, Im loading an entity 'Member' from its id in route data. [ListItemsForMembershipType(true)] public ActionResult Edit(Member someMember) {...} The attribute on the action loads the membership type list items for a dropdown box and sticks it in viewdata. This is fine for add forms, and search forms (it gets all active items) but I need the attribute to execute BASED ON THE VALUE someMember.MembershipTypeId, because its current value must always be present when loading the item (i.e. all active items, plus the one from the loaded record). So the question is, what is the standard pattern for this? How can my attribute accept the value or should I be loading the viewdata for the drop down in a controller supertype or during model binding or something else? It is in an attribute now because the code to set the viewdata would otherwise be duplicated in each usage in each action.

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  • user interface pattern for associating single or many objects to an entity

    - by Samuel
    Need suggestions on implementing associating single or many objects to an entity. All soccer team players are registered individually (e.g. they are part of 'players' table) A soccer team has many players. The click sequence is like this:- a] Soccer team owner provides a name and brief description of the soccer team. b] Now it wants to add players to this team. c] You have the following button 'Add players to team' which lets you navigate to the 'View Players' page and lets you multi select users from there. Assuming this is a paginated list of players, how do you handle the following:- Do you provide a check box against each player and let the manager do a multi selection. If you need to add more players, it doesn't make sense to show the players who have been already added to the team. Do you mark those entries as not selectable or you would adding showing these entries. If you need to filter, do you provide search filters at the top of this page. Am looking for ideas on how to implement this or sites which have already done something similar.

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  • Pattern for version-specific implementations of a Java class

    - by Mike Monkiewicz
    So here's my conundrum. I am programming a tool that needs to work on old versions of our application. I have the code to the application, but can not alter any of the classes. To pull information out of our database, I have a DTO of sorts that is populated by Hibernate. It consumes a data object for version 1.0 of our app, cleverly named DataObject. Below is the DTO class. public class MyDTO { private MyWrapperClass wrapper; public MyDTO(DataObject data) { wrapper = new MyWrapperClass(data); } } The DTO is instantiated through a Hibernate query as follows: select new com.foo.bar.MyDTO(t1.data) from mytable t1 Now, a little logic is needed on top of the data object, so I made a wrapper class for it. Note the DTO stores an instance of the wrapper class, not the original data object. public class MyWrapperClass { private DataObject data; public MyWrapperClass(DataObject data) { this.data = data; } public String doSomethingImportant() { ... version-specific logic ... } } This works well until I need to work on version 2.0 of our application. Now DataObject in the two versions are very similar, but not the same. This resulted in different sub classes of MyWrapperClass, which implement their own version-specific doSomethingImportant(). Still doing okay. But how does myDTO instantiate the appropriate version-specific MyWrapperClass? Hibernate is in turn instantiating MyDTO, so it's not like I can @Autowire a dependency in Spring. I would love to reuse MyDTO (and my dozens of other DTOs) for both versions of the tool, without having to duplicate the class. Don't repeat yourself, and all that. I'm sure there's a very simple pattern I'm missing that would help this. Any suggestions?

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  • Help with IE bugs when writing JSON via an ASPX response

    - by Jereme
    I have an ASPX page that I am using to write JSON. It works great in Firefox and Chrome, but when I try and use it in IE 8 it gives me an "The XML page cannot be displayed" error instead of allowing jQuery to load the JSON being written by the response. Any ideas? Here is what my code looks like: protected override void OnLoad(EventArgs e) { Response.Clear(); Response.ClearHeaders(); Response.ContentType = "application/json"; Response.Cache.SetCacheability(HttpCacheability.NoCache); Response.Write(string.Format("[ {{ \"Foo\": \"{0}\", \"bar\": \"{1}\" }} ]", "Foo Content", "Bar Content")); Response.End(); }

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  • Writing a script to bypass college login page

    - by gtredcvb
    My college has a silly login page that requires you to download a whole bunch of garbage that a lot of us don't need (Norton Anti-virus, Antispyware software, etc.). We have to have them running to get on the internet on campus. Though, if you are on Linux, or at least set your user-agent to linux, the requirements are gone. We could easily use Firefox with the useragent switcher to bypass this, but it'd be nice to create a script that automates this. How would this be possible? I figure this could be written in python, and could grab the webpage with curl specifying a user agent? How would I go about posting the data back to the servers? Thanks

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  • Generic Abstract Singleton with Custom Constructor in C#

    - by Heka
    I want to write a generic singleton with an external constructor. In other words the constructor can be modified. I have 2 designs in my mind but I don't know whether they are practical or not. First one is to enforce derived class' constructor to be non-public but I do not know if there is a way of it? Second one is to use a delegate and call it inside the constructor? It isn't necessarily to be a constructor. The reason I chose custom constructor is doing some custom initializations. Any suggestions would be appreciated :)

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  • What Is Utility Services ?

    - by query_bug
    Hai, I need some information about Utility Services Layer. Can someone Please help me in getting information on that as I am supposed to give a presentation on Utility Services Layer. Thanks in advance...

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  • Implementing a live voting system

    - by Will Eddins
    I'm looking at implementing a live voting system on my website. The website provides a live stream, and I'd like to be able to prompt viewers to select an answer during a vote initiated by the caster. I can understand how to store the data in a mySQL database, and how to process the answers. However: How would I initially start the vote on the client-side and display it? Should a script be running every few seconds on the page, checking another page to see if a question is available for the user? Are there any existing examples of a real-time polling system such as what I'm looking at implementing?

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