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  • Casting generics and the generic type

    - by Kragen
    Consider, I have the following 3 classes / interfaces: class MyClass<T> { } interface IMyInterface { } class Derived : IMyInterface { } And I want to be able to cast a MyClass<Derived> into a MyClass<IMyInterface> or visa-versa: MyClass<Derived> a = new MyClass<Derived>(); MyClass<IMyInterface> b = (MyClass<IMyInterface>)a; But I get compiler errors if I try: Cannot convert type 'MyClass<Derived>' to 'MyClass<IMyInterface>' I'm sure there is a very good reason why I cant do this, but I can't think of one. As for why I want to do this - The scenario I'm imagining is one whereby you ideally want to work with an instance of MyClass<Derived> in order to avoid lots of nasty casts, however you need to pass your instance to an interface that accepts MyClass<IMyInterface>. So my question is twofold: Why can I not cast between these two types? Is there any way of keeping the niceness of working with an instance of MyClass<Derived> while still being able to cast this into a MyClass<IMyInterface>?

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  • variables in abstract classes C++

    - by wyatt
    I have an abstract class CommandPath, and a number of derived classes as below: class CommandPath { public: virtual CommandResponse handleCommand(std::string) = 0; virtual CommandResponse execute() = 0; virtual ~CommandPath() {} }; class GetTimeCommandPath : public CommandPath { int stage; public: GetTimeCommandPath() : stage(0) {} CommandResponse handleCommand(std::string); CommandResponse execute(); }; All of the derived classes have the member variable 'stage'. I want to build a function into all of them which manipulates 'stage' in the same way, so rather than defining it many times I thought I'd build it into the parent class. I moved 'stage' from the private sections of all of the derived classes into the protected section of CommandPath, and added the function as follows: class CommandPath { protected: int stage; public: virtual CommandResponse handleCommand(std::string) = 0; virtual CommandResponse execute() = 0; std::string confirmCommand(std::string, int, int, std::string, std::string); virtual ~CommandPath() {} }; class GetTimeCommandPath : public CommandPath { public: GetTimeCommandPath() : stage(0) {} CommandResponse handleCommand(std::string); CommandResponse execute(); }; Now my compiler tells me for the constructor lines that none of the derived classes have a member 'stage'. I was under the impression that protected members are visible to derived classes? The constructor is the same in all classes, so I suppose I could move it to the parent class, but I'm more concerned about finding out why the derived classes aren't able to access the variable. Also, since previously I've only used the parent class for pure virtual functions, I wanted to confirm that this is the way to go about adding a function to be inherited by all derived classes.

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  • error: 'void Base::output()' is protected within this context

    - by Bill
    I'm confused about the errors generated by the following code. In Derived::doStuff, I can access Base::output directly by calling it. Why can't I create a pointer to output() in the same context that I can call output()? (I thought protected / private governed whether you could use a name in a specific context, but apparently that is incomplete?) Is my fix of writing callback(this, &Derived::output); instead of callback(this, Base::output) the correct solution? #include <iostream> using std::cout; using std::endl; template <typename T, typename U> void callback(T obj, U func) { ((obj)->*(func))(); } class Base { protected: void output() { cout << "Base::output" << endl; } }; class Derived : public Base { public: void doStuff() { // call it directly: output(); Base::output(); // create a pointer to it: // void (Base::*basePointer)() = &Base::output; // error: 'void Base::output()' is protected within this context void (Derived::*derivedPointer)() = &Derived::output; // call a function passing the pointer: // callback(this, &Base::output); // error: 'void Base::output()' is protected within this context callback(this, &Derived::output); } }; int main() { Derived d; d.doStuff(); }

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  • c++ Multiple Inheritance - Compiler modifying my pointers

    - by Bob
    If I run the following code, I get different addresses printed. Why? class Base1 { int x; }; class Base2 { int y; }; class Derived : public Base1, public Base2 { }; union U { Base2* b; Derived* d; U(Base2* b2) : b(b) {} }; int main() { Derived* d = new Derived; cout << d << "\n"; cout << U(d).d << "\n"; return 0; } Even more fun is if you repeatedly go in and out of the union the address keeps incrementing by 4, like this int main() { Derived* d = new Derived; cout << d << "\n"; d = U(d).d; cout << d << "\n"; d = U(d).d; cout << d << "\n"; return 0; } If the union is modified like this, then the problem goes away union U { void* v; Base2* b; Derived* d; U(void* v) : v(v) {} }; Also, if either base class is made empty, the problem goes away. Is this a compiler bug? I want it to leave my pointers the hell alone.

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  • Solaris 11 JDK installation

    - by user20121221
    JAVA -JDK install on Solaris 11 pkg list -s jdk-7 pkg install jdk-7 ls /usr/jdk/instances jdk1.5.0 jdk1.6.0 mv jdk1.7.0_07 /usr/jdk/instances/jdk1.7.0 ls -l total 9 drwxr-xr-x 5 root bin 5 Sep 4 16:08 instances lrwxrwxrwx 1 root root 18 Jul 14 11:11 jdk1.6.0_26 -> instances/jdk1.6.0 lrwxrwxrwx 1 root root 8 Sep 4 16:09 latest -> jdk1.6.0 drwxr-xr-x 4 root bin 4 Jul 14 11:04 packages rm latest ln -s instances/jdk1.7.0 jdk1.7.0_07 ln -s jdk1.7.0_07 latest cd /usr/ ls -ld java lrwxrwxrwx 1 root root 12 Sep 4 16:12 java -> jdk/jdk1.6.0 rm java ln -s jdk/latest java java -version java version "1.7.0_07"Java(TM) SE Runtime Environment (build 1.7.0_07-b10)Java HotSpot(TM) Server VM (build 23.3-b01, mixed mode) stop firefox cd /usr/lib/firefox/plugins rm libnpjp2.so ln -s /usr/jdk/jdk1.7.0_07/jre/lib/i386/libnpjp2.so libnpjp2.so start firefox

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  • How to save one role implementing a client/server pattern in Azure?

    - by Alfredo Delsors
    Sometimes you need to have an instance performing a server role when other instances are playing the client role. An example can be a file sharing like in this great post: http://blogs.msdn.com/b/mariok/archive/2011/02/11/sharing-folders-in-azure.aspx, one instance shares a folder that all other instances are using to write files that the server processes. The problem is that there is not discovering mechanism in Azure that allows one instance to know where the instance acting as a server is located. A first approach can be having a server role and a client role like in the previous post. This means more instances, more money. A solution to save this "server" role is to use Instance 0, always available, to act as a server. An instance can know that it should act as the server checking RoleEnvironment.CurrentRoleInstance.Id.EndsWith(".0"). Other instances can iterate the RoleEnvironment Instances collection to find the instance whose name ends with ".0", getting its endpoints and acting as its clients.

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  • How to make multiple instances of RCVR, RQSTR and CLUSRCVR channels in WMQ?

    - by Dr. Xray
    This is a follow up on the question below, but it deserves another question. http://stackoverflow.com/questions/1821514/are-server-conn-and-client-conn-channels-the-only-channels-that-could-have-more-t To my understanding, a receiver (or cluster receiver) channel usually pair up with a single sender (or cluster sender) channel. How can one side being single instance while the other side being multiple instances? Thanks.

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  • Why are member constants available even if there are no instances of a its class?

    - by flockofcode
    1) Why are member constants available even if there are no instances of a its class? 2) Is the only reason why constant expressions need to be fully evaluated at compile time due to compiler replacing constant variable with literal value? 3) Since string is also an object, I would think the following would produce an error, but it doesn’t. Why? class A { const string b = “it works”; } thank you

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  • What's the best way to stop multiple instances of a Windows app being launched?

    - by John
    Many Windows apps (like Skype or MSN for instance) don't let you start multiple instances, rather trying to run it a 2nd time just leaves the existing version running. Is this typically done in some simple way - the start-menu shortcut is a 'wrapper' app around the main app - or is there some registry magic you can do to delegate the problem to Windows itself? Specifically dealing with Win32 here (unmanaged C++) but happy to hear more general solutions as long as they are workable on Windows XP or alter.

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  • Ejabberd Clustering on EC2

    - by Architact
    I am trying to implement ejabberd clustering on Amazon EC2 instances, I have installed ejabberd and it is working fine on both instances, I can connect and send message, my first server is a master server and has the FQDN of master.example.com, second server is a slave and has FQDN of slave.example.com. I have edited the ejabberdctl.cfg file on both instances changed INET_DIST_INTERFACE on both instances to the value returned by ifconfig changed ERLANG_NODE to [email protected] on master and [email protected] on slave. Now when I run this command on slave net_adm:ping('[email protected]'). it always returns pang response indicating that it can't reach the master server. I am looking for possible fixes for that. Things already done Both master and slave domains are pointing to their instances I even tried allocating elastic ip and assigning that to instances, but did not help either. Any help will be greatly appreciated.

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  • How do you make a private member in the base class become a public member in the base class?

    - by jasonline
    Consider the following code: class Base { void f() { } }; class Derived: public Base { public: }; What can you change in the derived class, such that you can perform the following: Derived d; d.f(); If the member is declared as public in the base class, adding a using declaration for Base::f in the derived class public section would've fix the problem. But if it is declared as private in the base class, this doesn't seem to work.

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  • Auto update for application hosted on multiple servers on cloud

    - by mots_g
    I'm working on an application which will run on multiple Amazon EC2 instances. I wish to incorporate auto update feature for my application. The updater should update all the Ec2 instances. Also, there is a central server which governs the creation/termination of EC2 instances as per load. The central server creates a EC2 new instance from a pre-configured custom AMI (custom image which has our application pre-installed). Also, once there is an update, the pre-configured AMI needs to be updated too else it would create new instances which are not updated. Should the central server notify all the ec2 instances for an update and then the instances update themselves?Or should the application on Ec2 instance have a check for periodically updating themselves? Also how should the Amazon custom AMI be updated? Should a new instance be created from it, updated and then a new AMI be re-created and then new images be created from this AMI? What is the best way to incorporate an auto update feature for this architecture? The central server is written in Java and the application running on the cloud is written in C++. Is there a good framework available that can be used for this architecture? Please let me know on what I could be missing in the design and how it would help me to have a nice, extensible and fail safe auto update architecture. Thanks

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  • Pygame: Save a list of objects/classes/surfaces

    - by Sam Tubb
    I am working on a game, in which you can create mazes. You place blocks on a 16x16 grid, while choosing from a variety of block to make the level with. Whenever you create a block, it adds this class: class Block(object): def __init__(self,x,y,spr): self.x=x self.y=y self.sprite=spr self.rect=self.sprite.get_rect(x=self.x,y=self.y) to a list called instances. I tried shelving it to a .bin file, but it returns some error dealing with surfaces. How can I go about saving and loading levels? Any help is appreciated! :) Here is the whole code for reference: import pygame from pygame.locals import * #initstuff pygame.init() screen=pygame.display.set_mode((640,480)) pygame.display.set_caption('PiMaze') instances=[] #loadsprites menuspr=pygame.image.load('images/menu.png').convert() b1spr=pygame.image.load('images/b1.png').convert() b2spr=pygame.image.load('images/b2.png').convert() currentbspr=b1spr curspr=pygame.image.load('images/curs.png').convert() curspr.set_colorkey((0,255,0)) #menu menuspr.set_alpha(185) menurect=menuspr.get_rect(x=-260,y=4) class MenuItem(object): def __init__(self,pos,spr): self.x=pos[0] self.y=pos[1] self.sprite=spr self.pos=(self.x,self.y) self.rect=self.sprite.get_rect(x=self.x,y=self.y) class Block(object): def __init__(self,x,y,spr): self.x=x self.y=y self.sprite=spr self.rect=self.sprite.get_rect(x=self.x,y=self.y) while True: #menu items b1menu=b1spr.get_rect(x=menurect.left+32,y=48) b2menu=b2spr.get_rect(x=menurect.left+64,y=48) menuitems=[MenuItem(b1menu,b1spr),MenuItem(b2menu,b2spr)] screen.fill((20,30,85)) mse=pygame.mouse.get_pos() key=pygame.key.get_pressed() placepos=((mse[0]/16)*16,(mse[1]/16)*16) if key[K_q]: if mse[0]<260: if menurect.right<255: menurect.right+=1 else: if menurect.left>-260: menurect.left-=1 else: if menurect.left>-260: menurect.left-=1 for e in pygame.event.get(): if e.type==QUIT: exit() if menurect.right<100: if e.type==MOUSEBUTTONUP: if e.button==1: to_remove = [i for i in instances if i.rect.collidepoint(placepos)] for i in to_remove: instances.remove(i) if not to_remove: instances.append(Block(placepos[0],placepos[1],currentbspr)) for i in instances: screen.blit(i.sprite,i.rect) if not key[K_q]: screen.blit(curspr,placepos) screen.blit(menuspr,menurect) for item in menuitems: screen.blit(item.sprite,item.pos) if item.rect.collidepoint(mse): if pygame.mouse.get_pressed()==(1,0,0): currentbspr=item.sprite pygame.draw.rect(screen, ((255,0,0)), item, 1) pygame.display.flip()

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  • How to leverage the internal HTTP endpoint available on Azure web roles?

    - by adelsors
    Imagine you have a Web application using an in-memory collection that changes occasionally, loading it from storage on the Application_Start global.asax event and updating it whenever it changes. If you want to deploy this application on Azure you need to keep in mind that more than one instance of the application can be running at any time and therefore you need to provide some mechanism to keep all instances informed with the latest changes. Because that the communication through internal endpoints between Azure role instances is at no cost, a good solution can be maintaining the information on Azure Storage Tables, reading its contents on the Application_Start event and populating its changes to all instances using the internal HTTP port available on Azure Web Roles. You need to follow these steps to leverage the internal HTTP endpoint available on Azure web roles: 1.   Define an internal HTTP endpoint in the Web Role properties, for example InternalHttpEndpoint   2.   Add a new WCF service to the Web Role, for example NotificationServices.svc 3.   Add a method on the new service to receive notifications from other role instances. 4.   Declare a class that inherits from System.ServiceModel.Activation.ServiceHostFactory and override the method CreateServiceHost to host the internal endpoint.   Note that you can use SecurityMode.None because the internal endpoint is private to the instances of the service, this is provided by the platform. 5.   Edit the markup of the service right clicking the svc file and selecting "View markup" to add the new factory as the factory to be used to create the service    6. Now you can notify changes to other instances using this code:

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  • How to replace all instances of a particular value in a mysql database with another?

    - by Joseph
    I'm looking for a MySQL equivalent of what str_replace is for PHP. I want to replace all instances of one word with another, I want to run a query that will replace all "apples" with "oranges". The reason why: UPDATE fruits SET name='oranges' WHERE name='apples'; isn't going to work for my situation, is because I often times have multiple words in a table row separated by commas like: "apples, pears, pineapples". In this case I want just apples to be replaced by oranges and pear and pineapples to stay in tact. Is there any way to do this?

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  • Is there a jdbc driver for SQL Server that can search for database instances on network?

    - by djangofan
    Is there a jdbc driver for SQL Server that can search for database instances on network? Just wanting to emulate "OSQL -L" from the JDBC driver. Dont want to have to call OSQL from JNI or something. I also don't want to have to write my own code for scanning a UDP port. I want my Java application to be able to search for live SQL Servers and prompt me with a list of available servers. Isn't this a reasonable expectation for a JDBC driver? OSQL.exe can do it and so why not the JDBC driver?

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  • is it wasteful/bad design to use a vector/list where in most instances it will only have one element

    - by lucid
    is it wasteful/bad design to use a vector/list where in most instances it will only have one element? example: class dragon { ArrayList<head> = new ArrayList<head> Heads; tail Tail = new tail(); body Body = new body(); dragon() { theHead=new head(); Heads.add(theHead); } void nod() { for (int i=0;i<Heads.size();i++) { heads.get(i).GoUpAndDown(); } } } class firedragon extends dragon { } class icedragon extends dragon { } class lightningdragon extends dragon { } // 10 other one-headed dragon declarations here class hydra extends dragon { hydra() { anotherHead=new head(); for (int i=0;i<2;i++) { Heads.add(anotherHead); } } } class superhydra extends dragon { superhydra() { anotherHead=new head(); for (int i=0;i<4;i++) { Heads.add(anotherHead); } } }

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  • iPhone: How many instances of AVAudioPlayer should I have for multiple sounds?

    - by foreyez
    So I'm using AvAudioPlayer to play multiple wav files. About 20 different sounds (each about 1 sec long), and you can think of each being played on a button press. Also I don't need them all to play simultaneously, i.e., one plays and you press another button to play another one (which stops the currently played one). What I'm wondering, should I have multiple instances of AVAudioPlayer (20 of them) and then preload the audio files, or should I just use one instance of AvAudioPlayer and each time a button is pressed, initialize the AvAudioPlayer with the sound url (or would this be too slow?) Thanks in advance!

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