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  • Using forward declarations for build in datatypes.

    - by bdhar
    I understand that wherever possible we shall use forward declarations instead of includes to speed up the compilation. I have a class Person like this. #pragma once #include <string> class Person { public: Person(std::string name, int age); std::string GetName(void) const; int GetAge(void) const; private: std::string _name; int _age; }; and a class Student like this #pragma once #include <string> class Person; class Student { public: Student(std::string name, int age, int level = 0); Student(const Person& person); std::string GetName(void) const; int GetAge(void) const; int GetLevel(void) const; private: std::string _name; int _age; int _level; }; In Student.h, I have a forward declaration class Person; to use Person in my conversion constructor. Fine. But I have done #include <string> to avoid compilation error while using std::string in the code. How to use forward declaration here to avoid the compilation error? Is it possible? Thanks.

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  • Question about decorator pattern and the abstract decorator class?

    - by es11
    This question was asked already here, but rather than answering the specific question, descriptions of how the decorator pattern works were given instead. I'd like to ask it again because the answer is not immediately evident to me just by reading how the decorator pattern works (I've read the wikipedia article and the section in the book Head First Design Patterns). Basically, I want to know why an abstract decorator class must be created which implements (or extends) some interface (or abstract class). Why can't all the new "decorated classes" simply implement (or extend) the base abstract object themselves (instead of extending the abstract decorator class)? To make this more concrete I'll use the example from the design patterns book dealing with coffee beverages: There is an abstract component class called Beverage Simple beverage types such as HouseBlend simply extend Beverage To decorate beverage, an abstract CondimentDecorator class is created which extends Beverage and has an instance of Beverage Say we want to add a "milk" condiment, a class Milk is created which extends CondimentDecorator I'd like to understand why we needed the CondimentDecorator class and why the class Milk couldn't have simply extended the Beverage class itself and been passed an instance of Beverage in its constructor. Hopefully this is clear...if not I'd simply like to know why is the abstract decorator class necessary for this pattern? Thanks. Edit: I tried to implement this, omitting the abstract decorator class, and it seems to still work. Is this abstract class present in all descriptions of this pattern simply because it provides a standard interface for all of the new decorated classes?

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  • Problems running XNA game on 64-bit Windows 7

    - by Tesserex
    I'm having problems getting my game engine to run on my brother's machine, which is running 64-bit Windows 7. I'm developing on 32-bit XP SP2. My app uses XNA, FMOD.NET, and another dll I wrote entirely in C#. Everything is targeted to x86, not AnyCPU. I've read that this is required for XNA to work because there is no 64-bit xna framework. I recompiled FMOD.NET as x86 as well and made sure to be using the 32-bit version of the native dll. So I don't see any problems there. However when he tries to run my app, it gives an error which is mysterious, but not unheard of. A FileNotFoundException with an empty file name, and the top of the stack trace is in my main form constructor. The message is The specified module could not be found. (Exception from HRESULT: 0x8007007E) I found some threads online about this error, all with very vague, mixed, and fuzzy responses that don't really help me. Most remind people to target x86. Some say check that they have all the dlls necessary. I gave my brother Microsoft.Xna.Framework.dll, but does he need to install the entire XNA redistributable package? When I take everything I sent him and stick it in a random directory, it still runs fine for me. I developed the game in VS2008, not in game studio, using XNA 3.0 and a Windows Forms control that uses XNA drawing which I found in an msdn tutorial. I would also like to avoid requiring a full installer if possible. Any insight? Please?

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  • Html.ListBox() and MultiselectList

    - by Ivan90
    Hi guys, I've a little problem with an Html.ListBox! I am developing a personal blog in ASP.NET MVC 1.0 and I created an adminpanel where I can add and edit a post! During this two operations, I can add also tags! I think of use an Html.ListBox() helper to list all tags, and so I can select multiple tags to add in a post! The problem isn't during the add mode, but in the edit mode, where I have to pre-select post's tags! I read that I have to use a MultiSelectList and so in its constructor pass, tags' list and tag's list(pre-selected value). But I don't know how to use this class! I post, some code: This is my models method that get all list tags in selectlist public IEnumerable<SelectListItem> GetTagsListBox() { return from t in db.Tags orderby t.IDTag descending select new SelectListItem { Text = t.TagName, Value = t.IDTag.ToString(), }; } So in Edit (Get and Post), Add(Get and Post) I use a ViewData to pass this list in Html.ListBox(). ViewData["Tags"] = tagdb.GetTagsListBox(); And in my view <%=Html.ListBox("Tags",ViewData["Tags"] as SelectList) %> So with this code it's ok in Add Mode! But in Edit Mode I need to pre-select those values! So Now, of course I have to create a method that get all tagsbypostid! and then in ViewData what Must I to pass? Any suggest?

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  • why am I stuck on "Initiating update" when deploying to google

    - by michelle
    I've have not had any trouble deploying through eclipse until now. I'm guessing it might have to do with all the stuff I've added today a folder of .pdf and .tex files (in war/web-inf directory) a bit of JDO stuff and a servlet that reads the files in the directory and indexes them into the JDO Is there any way to find out what exactly is the problem? I currently get stuck at "Initiating update" and the stack trace say "ConnectionReset" Any helkp of imput will be appreciated, I really need to deploy this today, thanks! here's the deploy trace: Unable to update: java.net.SocketException: Connection reset at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at sun.net.www.protocol.http.HttpURLConnection$6.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at sun.net.www.protocol.http.HttpURLConnection.getChainedException(Unknown Source) at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source) at java.net.HttpURLConnection.getResponseCode(Unknown Source) at com.google.appengine.tools.admin.ServerConnection.getAuthCookie(ServerConnection.java:315) at com.google.appengine.tools.admin.ServerConnection.authenticate(ServerConnection.java:219) at com.google.appengine.tools.admin.ServerConnection.send(ServerConnection.java:145) at com.google.appengine.tools.admin.ServerConnection.post(ServerConnection.java:81) at com.google.appengine.tools.admin.AppVersionUpload.send(AppVersionUpload.java:427) at com.google.appengine.tools.admin.AppVersionUpload.beginTransaction(AppVersionUpload.java:241) at com.google.appengine.tools.admin.AppVersionUpload.doUpload(AppVersionUpload.java:98) at com.google.appengine.tools.admin.AppAdminImpl.update(AppAdminImpl.java:56) at com.google.appengine.eclipse.core.proxy.AppEngineBridgeImpl.deploy(AppEngineBridgeImpl.java:271) at com.google.appengine.eclipse.core.deploy.DeployProjectJob.runInWorkspace(DeployProjectJob.java:148) at org.eclipse.core.internal.resources.InternalWorkspaceJob.run(InternalWorkspaceJob.java:38) at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55) Caused by: java.net.SocketException: Connection reset at java.net.SocketInputStream.read(Unknown Source) at java.io.BufferedInputStream.fill(Unknown Source) at java.io.BufferedInputStream.read1(Unknown Source) at java.io.BufferedInputStream.read(Unknown Source) at sun.net.www.http.HttpClient.parseHTTPHeader(Unknown Source) at sun.net.www.http.HttpClient.parseHTTP(Unknown Source) at sun.net.www.http.HttpClient.parseHTTP(Unknown Source) at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source) at sun.net.www.protocol.http.HttpURLConnection.getHeaderFieldKey(Unknown Source) at com.google.appengine.tools.util.ClientCookieManager.readCookies(ClientCookieManager.java:123) at com.google.appengine.tools.admin.ServerConnection.connect(ServerConnection.java:340) at com.google.appengine.tools.admin.ServerConnection.getAuthCookie(ServerConnection.java:314) ... 11 more

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  • Declaring a string array in class header file - compiler thinks string is variable name?

    - by Dave
    Hey everybody, I need a bit of a hand with declaring a string array in my class header file in C++. atm it looks like this: //Maze.h #include <string> class Maze { GLfloat mazeSize, mazeX, mazeY, mazeZ; string* mazeLayout; public: Maze ( ); void render(); }; and the constructor looks like this: //Maze.cpp #include <GL/gl.h> #include "Maze.h" #include <iostream> #include <fstream> Maze::Maze( ) { cin >> mazeSize; mazeLayout = new string[mazeSize]; mazeX = 2/mazeSize; mazeY = 0.25; mazeZ = 2/mazeSize; } I'm getting a compiler error that says: In file included from model-view.cpp:11: Maze.h:14: error: ISO C++ forbids declaration of ‘string’ with no type Maze.h:14: error: expected ‘;’ before ‘*’ token and the only sense that makes to me is that for some reason it thinks I want string as a variable name not as a type declaration. If anybody could help me out that would be fantastic, been looking this up for a while and its giving me the shits lol. Cheers guys

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  • Prototypal inheritance should save memory, right?

    - by Techpriester
    Hi Folks, I've been wondering: Using prototypes in JavaScript should be more memory efficient than attaching every member of an object directly to it for the following reasons: The prototype is just one single object. The instances hold only references to their prototype. Versus: Every instance holds a copy of all the members and methods that are defined by the constructor. I started a little experiment with this: var TestObjectFat = function() { this.number = 42; this.text = randomString(1000); } var TestObjectThin = function() { this.number = 42; } TestObjectThin.prototype.text = randomString(1000); randomString(x) just produces a, well, random String of length x. I then instantiated the objects in large quantities like this: var arr = new Array(); for (var i = 0; i < 1000; i++) { arr.push(new TestObjectFat()); // or new TestObjectThin() } ... and checked the memory usage of the browser process (Google Chrome). I know, that's not very exact... However, in both cases the memory usage went up significantly as expected (about 30MB for TestObjectFat), but the prototype variant used not much less memory (about 26MB for TestObjectThin). I also checked: The TestObjectThin instances contain the same string in their "text" property, so they are really using the property of the prototype. Now, I'm not so sure what to think about this. The prototyping doesn't seem to be the big memory saver at all. I know that prototyping is a great idea for many other reasons, but I'm specifically concerned with memory usage here. Any explanations why the prototype variant uses almost the same amount of memory? Am I missing something?

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  • How does one create and use a pointer to an array of an unknown number of structures inside a class?

    - by user1658731
    Sorry for the confusing title... I've been playing around with C++, working on a project to parse a game's (Kerbal Space Program) save file so I can modify it and eventually send it over a network. I'm stuck with storing an unknown number of vessels and crew members, so I need to have an array of unknown size. Is this possible? I figured having a pointer to an array would be the way to go. I have: class SaveFileSystem { string version; string UT; int activeVessel; int numCrew; ??? Crews; // !! int numVessels; ??? Vessels; // !! } Where Crews and Vessels should be arrays of structures: struct Crew { string name; //Other stuff }; struct Vessel { string name; //Stuff }; I'm guessing I should have something like: this->Crews = new ???; this->Vessels = new ???; in my constructor to initialize the arrays, and attempt to access it with: this->Crews[0].name = "Ship Number One"; Does this make any sense??? I'd expect the "???"'s to involve a mess of asterisk's, like "*struct (*)Crews" but I have no real idea. I've got normal pointers down and such, but this is a tad over my head... I'd like to access the structures like in the last snippet, but if C++ doesn't like that I could do pointer arithmetic. I've looked into vectors, but I have an unhealthy obsession with efficiency, and it really pains me how you don't know what's going on behind it.

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  • C# ref Confusion

    - by Rahat
    I have a confusion that when i pass a variable by refrence in the constructor of another class and after passing that object by refrence i recreate the refrence object with the new keyword. Now the class in which i have passed the refrenced object dosen't reflect the updated data. An exabple of the above problem is shown below: Object to be passed by Refrence: public class DummyObject { public string Name = "My Name"; public DummyObject() { } } Class which is passing the Refrence: public partial class Form1 : Form { // Object to be passed as refrence DummyObject dummyObject = new DummyObject(); public Form1() { InitializeComponent(); } private void button1_Click(object sender, EventArgs e) { // assigning value dummyObject.Name = "I am Dummy"; // Passing object Form2 frm = new Form2(ref dummyObject); frm.Show(); } private void button2_Click(object sender, EventArgs e) { // Displaying Name MessageBox.Show(this.dummyObject.Name); } private void button3_Click(object sender, EventArgs e) { // Assigning new object this.dummyObject = new DummyObject(); // Changing Name Variable this.dummyObject.Name = "I am Rechanged"; // Displaying Name MessageBox.Show(this.dummyObject.Name); } } Class to which Object is passed by Reference: public partial class Form2 : Form { private DummyObject dummyObject = null; public Form2(ref DummyObject DummyObject) { InitializeComponent(); this.dummyObject = DummyObject; this.dummyObject.Name = "I am Changed"; } private void button2_Click(object sender, EventArgs e) { MessageBox.Show(this.dummyObject.Name); } } whn i reaasign the object in Form 1 and cdisplay its value in form 2 it still displays "I am Changed" instead of "I am Rechanged". How to keep the data synchronized?

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  • Handling selection and deselection of objects in a user interface

    - by Dennis
    I'm writing a small audio application (in Silverlight, but that's not really relevant I suppose), and I'm a struggling with a problem I've faced before and never solved properly. This time I want to get it right. In the application there is one Arrangement control, which contains several Track controls, and every Track can contain AudioObject controls (these are all custom user controls). The user needs to be able to select audio objects, and when these objects are selected they are rendered differently. I can make this happen by hooking into the MouseDown event of the AudioObject control and setting state accordingly. So far so good, but when an audio object is selected, all other audio objects need to be deselected (well, unless the user holds the shift key). Audio objects don't know about other audio objects though, so they have no way to tell the rest to deselect themselves. Now if I would approach this problem like I did the last time I would pass a reference to the Arrangement control in the constructor of the AudioObject control and give the Arrangement control a DeselectAll() method or something like that, which would tell all Track controls to deselect all their AudioObject controls. This feels wrong, and if I apply this strategy to similar issues I'm afraid I will soon end up with every object having a reference to every other object, creating one big tightly coupled mess. It feels like opening the floodgates for poorly designed code. Is there a better way to handle this?

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  • Java KeyListener in separate class

    - by Chris
    So I have my main class here, where basically creates a new jframe and adds a world object to it. The world object is basically where all drawing and keylistening would take place... public class Blobs extends JFrame{ public Blobs() { super("Blobs :) - By Chris Tanaka"); setVisible(true); setResizable(false); setSize(1000, 1000); setIgnoreRepaint(true); setDefaultCloseOperation(EXIT_ON_CLOSE); add(new World()); } public static void main(String[] args) { new Blobs(); } } How exactly would you get key input from the world class? (So far I have my world class extending a jpanel and implementing a keylistener. In the constructor i addKeyListener(this). I also have these methods since they are auto implemented: public void keyPressed(KeyEvent e) { if (e.getKeyCode() == KeyEvent.VK_W) System.out.println("Hi"); } public void keyReleased(KeyEvent e) {} public void keyTyped(KeyEvent e) {} However this does not seem to work?

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  • QT QSslError being signaled with the error code set to NoError

    - by Nantucket
    My Problem I compiled OpenSSL into QT to enable OpenSSL support. Everything appeared to go correctly in the compile. However, when I try to use the official HTTP example application that can be found here, everytime I try to download an https page, it will signal two QSslError, each with contents NoError. The types of QSslErrors, including NoError, are documented here, poorly. There is no explanation on why they even included an error type called NoError, or what it means. Bizarrely, the NoError error code seems to be true, as it downloads the remote https document perfectly even while signaling the error. Does anyone have any idea what this means and what could possibly be causing it? Optional Background Reading Here is the relevant part of the code from the example app (this is connected to the network connection's sslErrors signal by the constructor): void HttpWindow::sslErrors(QNetworkReply*,const QList<QSslError> &errors) { QString errorString; foreach (const QSslError &error, errors) { if (!errorString.isEmpty()) errorString += ", "; errorString += error.errorString(); } if (QMessageBox::warning(this, tr("HTTP"), tr("One or more SSL errors has occurred: %1").arg(errorString), QMessageBox::Ignore | QMessageBox::Abort) == QMessageBox::Ignore) { reply->ignoreSslErrors(); } } I have tried the old version of this example, and it produced the same result. I have tried OpenSSL 1.0.0a and 0.9.8o. I have tried tried compiling OpenSSL myself, I have tried using pre-compiled versions of OpenSSL from the net. All produce the same result. If this were my first time using QT with SSL, I would almost think this is the intended result (even though their example application is popping up error warning message windows), if not for the fact that last time I played with QT, using what would now be an old version of QT with an old version of SSL, I distinctly remember everything working fine with no error windows. My system is running Windows 7 x64.

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  • hadoop implementing a generic list writable

    - by Guruprasad Venkatesh
    I am working on building a map reduce pipeline of jobs(with one MR job's output feeding to another as input). The values being passed around are fairly complex, in that there are lists of different types and hash maps with values as lists. Hadoop api does not seem to have a ListWritable. Am trying to write a generic one, but it seems i can't instantiate a generic type in my readFields implementation, unless i pass in the class type itself: public class ListWritable<T extends Writable> implements Writable { private List<T> list; private Class<T> clazz; public ListWritable(Class<T> clazz) { this.clazz = clazz; list = new ArrayList<T>(); } @Override public void write(DataOutput out) throws IOException { out.writeInt(list.size()); for (T element : list) { element.write(out); } } @Override public void readFields(DataInput in) throws IOException{ int count = in.readInt(); this.list = new ArrayList<T>(); for (int i = 0; i < count; i++) { try { T obj = clazz.newInstance(); obj.readFields(in); list.add(obj); } catch (InstantiationException e) { e.printStackTrace(); } catch (IllegalAccessException e) { e.printStackTrace(); } } } } But hadoop requires all writables to have a no argument constructor to read the values back. Has anybody tried to do the same and solved this problem? TIA.

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  • Jasmine testing coffeescript expect(setTimeout).toHaveBeenCalledWith

    - by Lee Quarella
    In the process of learning Jasmine, I've come to this issue. I want a basic function to run, then set a timeout to call itself again... simple stuff. class @LoopObj constructor: -> loop: (interval) -> #do some stuff setTimeout((=>@loop(interval)), interval) But I want to test to make sure the setTimeout was called with the proper args describe "loop", -> xit "does nifty things", -> it "loops at a given interval", -> my_nifty_loop = new LoopObj interval = 10 spyOn(window, "setTimeout") my_nifty_loop.loop(interval) expect(setTimeout).toHaveBeenCalledWith((-> my_nifty_loop.loop(interval)), interval) I get this error: Expected spy setTimeout to have been called with [ Function, 10 ] but was called with [ [ Function, 10 ] ] Is this because the (-> my_nifty_loop.loop(interval)) function does not equal the (=>@loop(interval)) function? Or does it have something to do with the extra square brackets around the second [ [ Function, 10 ] ]? Something else altogther? Where have I gone wrong?

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  • Remove pointer object whose reference is mantained in three different lists

    - by brainydexter
    I am not sure how to approach this problem: 'Player' class mantains a list of Bullet* objects: class Player { protected: std::list< Bullet* > m_pBullet_list; } When the player fires a Bullet, it is added to this list. Also, inside the constructor of bullet, a reference of the same object is updated in CollisionMgr, where CollisionMgr also mantains a list of Bullet*. Bullet::Bullet(GameGL*a_pGameGL, Player*a_pPlayer) : GameObject( a_pGameGL ) { m_pPlayer = a_pPlayer; m_pGameGL->GetCollisionMgr()->AddBullet(this); } class CollisionMgr { void AddBullet(Bullet* a_pBullet); protected: std::list< Bullet*> m_BulletPList; } In CollisionMgr.Update(); based on some conditions, I populate class Cell which again contain a list of Bullet*. Finally, certain conditions qualify a Bullet to be deleted. Now, these conditions are tested upon while iterating through a Cell's list. So, if I have to delete the Bullet object, from all these places, how should I do it so that there are no more dangling references to it? std::list< Bullet*>::iterator bullet_it; for( bullet_it = (a_pCell->m_BulletPList).begin(); bullet_it != (a_pCell->m_BulletPList).end(); bullet_it++) { bool l_Bullet_trash = false; Bullet* bullet1 = *bullet_it; // conditions would set this to true if ( l_Bullet_Trash ) // TrashBullet( bullet1 ); continue; } Also, I was reading about list::remove, and it mentions that it calls the destructor of the object we are trying to delete. Given this info, if I delete from one list, the object does not exist, but the list would still contain a reference to it..How do I handle all these problems ? Can someone please help me here ? Thanks PS: If you want me to post more code or provide explanation, please do let me know.

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  • Low-Hanging Fruit: Obfuscating non-critical values in JavaScript

    - by Piskvor
    I'm making an in-browser game of the type "guess what place/monument/etc. is in this satellite/aerial view", using Google Maps JS API v3. However, I need to protect against cheaters - you have to pass a google.maps.LatLng and a zoom level to the map constructor, which means a cheating user only needs to view source to get to this data. I am already unsetting every value I possibly can without breaking the map (such as center and the manipulation functions like setZoom()), and initializing the map in an anonymous function (so the object is not visible in global namespace). Now, this is of course in-browser, client-side, untrusted JavaScript; I've read much of the obfuscation tag and I'm not trying to make the script bullet-proof (it's just a game, after all). I only need to make the obfuscation reasonably hard against the 1337 Java5kryp7 haxz0rz - "kid sister encryption", as Bruce Schneier puts it. Anything harder than base64 encoding would deter most cheaters by eliminating the lowest-hanging fruit - if the cheater is smart and determined enough to use a JS debugger, he can bypass anything I can do (as I need to pass the value to Google Maps API in plaintext), but that's unlikely to happen on a mass scale (there will also be other, not-code-related ways to prevent cheating). I've tried various minimizers and obfuscators, but those will mostly deal with code - the values are still shown verbatim. TL;DR: I need to obfuscate three values in JavaScript. I'm not looking for bullet-proof armor, just a sneeze-guard. What should I use?

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  • KeyStore, HttpClient, and HTTPS: Can someone explain this code to me?

    - by stormin986
    I'm trying to understand what's going on in this code. KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType()); FileInputStream instream = new FileInputStream(new File("my.keystore")); try { trustStore.load(instream, "nopassword".toCharArray()); } finally { instream.close(); } SSLSocketFactory socketFactory = new SSLSocketFactory(trustStore); Scheme sch = new Scheme("https", socketFactory, 443); httpclient.getConnectionManager().getSchemeRegistry().register(sch); My Questions: trustStore.load(instream, "nopassword".toCharArray()); is doing what exactly? From reading the documentation load() will load KeyStore data from an input stream (which is just an empty file we just created), using some arbitrary "nopassword". Why not just load it with null as the InputStream parameter and an empty string as the password field? And then what is happening when this empty KeyStore is being passed to the SSLSocketFactory constructor? What's the result of such an operation? Or -- is this simply an example where in a real application you would have to actually put a reference to an existing keystore file / password?

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  • How can you connect to a password protected MS Access Database from a Spring JdbcTemplate?

    - by Tim Visher
    I need to connect to a password protected MS Access 2003 DB using the JDBC-ODBC bridge. I can't find out how to specify the password in the connect string, or even if that is the correct method of connecting. It would probably be relevant to mention that this is a Spring App which is accessing the database through a JdbcTemplate configured as a datasource bean in our application context file. Some relevant snippets: from application-context.xml <bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate"> <property name="dataSource" ref="legacyDataSource" /> </bean> <bean id="jobsheetLocation" class="java.lang.String"> <constructor-arg value="${jobsheet.location}"/> </bean> <bean id="legacyDataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource"> <property name="driverClassName" value="${jdbc.legacy.driverClassName}" /> <property name="url" value="${jdbc.legacy.url}"/> <property name="password" value="-------------" /> </bean> from our build properties jdbc.legacy.driverClassName=sun.jdbc.odbc.JdbcOdbcDriver jdbc.legacy.url=jdbc:odbc:Driver\={Microsoft Access Driver (*.mdb)};Dbq\=@LegacyDbPath@;DriverID\=22;READONLY\=true Any thoughts?

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  • Immutable classes in C++

    - by ereOn
    Hi, In one of my projects, I have some classes that represent entities that cannot change once created, aka. immutable classes. Example : A class RSAKey that represent a RSA key which only has const methods. There is no point changing the existing instance: if you need another one, you just create one. My objects sometimes are heavy and I enforced the use of smart pointers to avoid copy. So far, I have the following pattern for my classes: class RSAKey : public boost::noncopyable, public boost::enable_shared_from_this<RSAKey> { public: /** * \brief Some factory. * \param member A member value. * \return An instance. */ static boost::shared_ptr<const RSAKey> createFromMember(int member); /** * \brief Get a member. * \return The member. */ int getMember() const; private: /** * \brief Constructor. * \param member A member. */ RSAKey(int member); /** * \brief Member. */ const int m_member; }; So you can only get a pointer (well, a smart pointer) to a const RSAKey. To me, it makes sense, because having a non-const reference to the instance is useless (it only has const methods). Do you guys see any issue regarding this pattern ? Are immutable classes something common in C++ or did I just created a monster ? Thank you for your advices !

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  • Using generics in F# to create an EnumArray type

    - by Matthew
    I've created an F# class to represent an array that allocates one element for each value of a specific enum. I'm using an explicit constructor that creates a dictionary from enum values to array indices, and an Item property so that you can write expressions like: let my_array = new EnumArray<EnumType, int> my_array.[EnumType.enum_value] <- 5 However, I'm getting the following obscure compilation error at the line marked with '// FS0670' below. error FS0670: This code is not sufficiently generic. The type variable ^e when ^e : enum<int> and ^e : equality and ^e : (static member op_Explicit : ^e -> int) could not be generalized because it would escape its scope. I'm at a loss - can anyone explain this error? type EnumArray< 'e, 'v when 'e : enum<int> and 'e : equality and ^e : (static member op_Explicit : ^e -> int) > = val enum_to_int : Dictionary<'e, int> val a : 'v array new() as this = { enum_to_int = new Dictionary<'e, int>() a = Array.zeroCreate (Enum.GetValues(typeof<'e>).Length) } then for (e : obj) in Enum.GetValues(typeof<'e>) do this.enum_to_int.Add(e :?> 'e, int(e :?> 'e)) member this.Item with get (idx : 'e) : 'v = this.a.[this.enum_to_int.[idx]] // FS0670 and set (idx : 'e) (c : 'v) = this.a.[this.enum_to_int.[idx]] <- c

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  • Working with complex objects in Prevayler commands

    - by alexantd
    The demos included in the Prevayler distribution show how to pass in a couple strings (or something simple like that) into a command constructor in order to create or update an object. The problem is that I have an object called MyObject that has a lot of fields. If I had to pass all of them into the CreateMyObject command manually, it would be a pain. So an alternative I thought of is to pass my business object itself into the command, but to hang onto a clone of it (keeping in mind that I can't store the BO directly in the command). Of course after executing this command, I would need to make sure to dispose of the original copy that I passed in. public class CreateMyObject implements TransactionWithQuery { private MyObject object; public CreateMyObject(MyObject business_obj) { this.object = (MyObject) business_obj.clone(); } public Object executeAndQuery(...) throws Exception { ... } } The Prevayler wiki says: Transactions can't carry direct object references (pointers) to business objects. This has become known as the baptism problem because it's a common beginner pitfall. Direct object references don't work because once a transaction has been serialized to the journal and then deserialized for execution its object references no longer refer to the intended objects - - any objects they may have referred to at first will have been copied by the serialization process! Therefore, a transaction must carry some kind of string or numeric identifiers for any objects it wants to refer to, and it must look up the objects when it is executed. I think by cloning the passed-in object I will be getting around the "direct object pointer" problem, but I still don't know whether or not this is a good idea...

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  • Textfield - what is wxTextCtrlNameStr?

    - by Wallter
    I'm trying to create a basic wxWidgets program with a text entry box, in the constructor there is a variable wxTextCtrlNameStr - in researching I can't seem to find wxTextCtrlNameStr? any help? wxTextCtrl(wxWindow* parent, wxWindowID id, const wxString& value = "", const wxPoint& pos = wxDefaultPosition, const wxSize& size = wxDefaultSize, long style = 0, const wxValidator& validator = wxDefaultValidator, const wxString& name = wxTextCtrlNameStr) My Code: MainFrame::MainFrame(const wxString& title) : wxFrame(NULL, wxID_ANY, title) { wxButton * Centigrade = new wxButton(this, BUTTON_CENTIGRADE, _T("to Centigrade"), wxPoint(20, 20), wxDefaultSize, 0); wxButton * Fahrenheit = new wxButton(this, BUTTON_FAHRENHEIT, _T("to Fahrenheit"), wxPoint(20, 40), wxDefaultSize, 0); F_txt = new wxTextCtrl(this, TXT_F_Main, "0", wxDefaultPosition, wxDefaultSize, wxDefaultValidator, wxTextCtrlNameStr); /***********************************************/ C_txt = new wxTextCtrl(this, TXT_C_Main, "0", wxDefaultPosition, wxDefaultSize, wxDefaultValidator, wxTextCtrlNameStr); /***********************************************/ ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ...

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  • how to get access to private members of nested class?

    - by macias
    Background: I have enclosed (parent) class E with nested class N with several instances of N in E. In the enclosed (parent) class I am doing some calculations and I am setting the values for each instance of nested class. Something like this: n1.field1 = ...; n1.field2 = ...; n1.field3 = ...; n2.field1 = ...; ... It is one big eval method (in parent class). My intention is -- since all calculations are in parent class (they cannot be done per nested instance because it would make code more complicated) -- make the setters only available to parent class and getters public. And now there is a problem: when I make the setters private, parent class cannot acces them when I make them public, everybody can change the values and C# does not have friend concept I cannot pass values in constructor because lazy evaluation mechanism is used (so the instances have to be created when referencing them -- I create all objects and the calculation is triggered on demand) I am stuck -- how to do this (limit access up to parent class, no more, no less)? I suspect I'll get answer-question first -- "but why you don't split the evaluation per each field" -- so I answer this by example: how do you calculate min and max value of a collection? In a fast way? The answer is -- in one pass. This is why I have one eval function which does calculations and sets all fields at once.

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  • Having issues with initializing character array

    - by quandrum
    Ok, this is for homework about hashtables, but this is the simple stuff I thought I was able to do from earlier classes, and I'm tearing my hair out. The professor is not being responsive enough, so I thought I'd try here. We have a hashtable of stock objects.The stock objects are created like so: stock("IBM", "International Business Machines", 2573, date(date::MAY, 23, 1967)) my constructor looks like: stock::stock(char const * const symbol, char const * const name, int sharePrice, date priceDate): symbol(NULL), name(NULL), sharePrice(sharePrice), dateOfPrice(priceDate) { setSymbol(symbol); setName(name); } and setSymbol looks like this: (setName is indentical): void stock::setSymbol(const char* symbol) { if (this->symbol) delete [] this->symbol; this->symbol = new char[strlen(symbol)+1]; strcpy(this->symbol,symbol); } and it refuses to allocate on the line this->symbol = new char[strlen(symbol)+1]; with a std::bad_alloc. name and symbol are declared char * name; char * symbol; I feel like this is exactly how I've done it in previous code.I'm sure it's something silly with pointers. Can anyone help?

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  • Why is F# member not found when used in subclass

    - by James Black
    I have a base type that I want to inherit from, for all my DAO objects, but this member gets the error further down about not being defined: type BaseDAO() = member v.ExecNonQuery2(conn)(sqlStr) = let comm = new MySqlCommand(sqlStr, conn, CommandTimeout = 10) comm.ExecuteNonQuery |> ignore comm.Dispose |> ignore I inherit in this type: type CreateDatabase() = inherit BaseDAO() member private self.createDatabase(conn) = self.ExecNonQuery2 conn "DROP DATABASE IF EXISTS restaurant" This is what I see when my script runs in the interactive shell: --> Referenced 'C:\Program Files\MySQL\MySQL Connector Net 6.2.3\Assemblies\MySql.Data.dll' [Loading C:\Users\jblack\Documents\Visual Studio 2010\Projects\RestaurantService\RestaurantDAO\BaseDAO.fs] namespace FSI_0106.RestaurantServiceDAO type BaseDAO = class new : unit -> BaseDAO member ExecNonQuery2 : conn:MySql.Data.MySqlClient.MySqlConnection -> sqlStr:string -> unit member execNonQuery : sqlStr:string -> unit member execQuery : sqlStr:string * selectFunc:(MySql.Data.MySqlClient.MySqlDataReader -> 'a list) -> 'a list member f : x:obj -> string member Conn : MySql.Data.MySqlClient.MySqlConnection end [Loading C:\Users\jblack\Documents\Visual Studio 2010\Projects\RestaurantService\RestaurantDAO\CreateDatabase.fs] C:\Users\jblack\Documents\Visual Studio 2010\Projects\RestaurantService\RestaurantDAO\CreateDatabase.fs(56,14): error FS0039: The field, constructor or member 'ExecNonQuery2' is not defined I am curious what I am doing wrong. I have tried not inheriting, and just instantiating the BaseDAO type in the function, but I get the same error. I started on this path because I had a property that had the same error, so it seems there may be a problem with how I am defining my BaseDAO type, but it compiles with no error, which further confuses me about this problem.

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