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  • Why is 'virtual' optional for overridden methods in derived classes?

    - by squelart
    When a method is declared as virtual in a class, its overrides in derived classes are automatically considered virtual as well, and the C++ language makes this keyword virtual optional in this case: class Base { virtual void f(); }; class Derived : public Base { void f(); // 'virtual' is optional but implied. }; My question is: What is the rationale for making virtual optional? I know that it is not absolutely necessary for the compiler to be told that, but I would think that developers would benefit if such a constraint was enforced by the compiler. E.g., sometimes when I read others' code I wonder if a method is virtual and I have to track down its superclasses to determine that. And some coding standards (Google) make it a 'must' to put the virtual keyword in all subclasses.

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  • cast operator to base class within a thin wrapper derived class

    - by miked
    I have a derived class that's a very thin wrapper around a base class. Basically, I have a class that has two ways that it can be compared depending on how you interpret it so I created a new class that derives from the base class and only has new constructors (that just delegate to the base class) and a new operator==. What I'd like to do is overload the operator Base&() in the Derived class so in cases where I need to interpret it as the Base. For example: class Base { Base(stuff); Base(const Base& that); bool operator==(Base& rhs); //typical equality test }; class Derived : public Base { Derived(stuff) : Base(stuff) {}; Derived(const Base& that) : Base(that) {}; Derived(const Derived& that) : Base(that) {}; bool operator==(Derived& rhs); //special case equality test operator Base&() { return (Base&)*this; //Is this OK? It seems wrong to me. } }; If you want a simple example of what I'm trying to do, pretend I had a String class and String==String is the typical character by character comparison. But I created a new class CaseInsensitiveString that did a case insensitive compare on CaseInsensitiveString==CaseInsensitiveString but in all other cases just behaved like a String. it doesn't even have any new data members, just an overloaded operator==. (Please, don't tell me to use std::string, this is just an example!) Am I going about this right? Something seems fishy, but I can't put my finger on it.

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  • Is it possible to run multiple instances/windows of Finder in Mac OS X?

    - by sunpech
    Mac OS X's Finder seems to be the equivalent to Windows Explorer. In Windows, I enjoy having multiple instances of Explorer open to move/copy files from one folder in a window, to another folder in another window. How can I achieve this in Snow Leopard? I'd like to have shortcut key, as well as a dock icon solution. Or maybe there's a better program than Finder out there that does this?

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  • SQL Server Integration Services 2008: Importing Excel Data Using Derived Column Transformation

    The complexity involved in transferring data between Excel and SQL Server results from different and sometimes incompatible data types. The Import and Export wizard mitigates potential issues introduced by these incompatibilities by taking advantage of Data Conversion Transformation. Marcin Policht describes another approach that produces an equivalent outcome by employing Derived Column Transformation instead.

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  • Why no multiple instances of Firefox on Linux as on Windows?

    - by Jack
    On Windows If I run Firefox as user jack, and then try to start another instance of firefox I will be unable to, as one is already running. If I choose to run firefox as administrator, then I can have two instances of firefox, separate from each other side by side, because they are under different user accounts. This does not seem to be true on Linux. As user jack if I start firefox, like on windows I am unable to start a new instance. If I open a terminal and change to root, set XAUTHORITY to jacks .Xauthority and try to start firefox as root....I get the error that firefox is already running. Why is this? Please don't spare any technical details in your answers....thankyou.

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  • Operator== in derived class never gets called.

    - by Robin Welch
    Can someone please put me out of my misery with this? I'm trying to figure out why a derived operator== never gets called in a loop. To simplify the example, here's my Base and Derived class: class Base { // ... snipped bool operator==( const Base& other ) const { return name_ == other.name_; } }; class Derived : public Base { // ... snipped bool operator==( const Derived& other ) const { return ( static_cast<const Base&>( *this ) == static_cast<const Base&>( other ) ? age_ == other.age_ : false ); }; Now when I instantiate and compare like this ... Derived p1("Sarah", 42); Derived p2("Sarah", 42); bool z = ( p1 == p2 ); ... all is fine. Here the operator== from Derived gets called, but when I loop over a list, comparing items in a list of pointers to Base objects ... list<Base*> coll; coll.push_back( new Base("fred") ); coll.push_back( new Derived("sarah", 42) ); // ... snipped // Get two items from the list. Base& obj1 = **itr; Base& obj2 = **itr2; cout << obj1.asString() << " " << ( ( obj1 == obj2 ) ? "==" : "!=" ) << " " << obj2.asString() << endl; Here asString() (which is virtual and not shown here for brevity) works fine, but obj1 == obj2 always calls the Base operator== even if the two objects are Derived. I know I'm going to kick myself when I find out what's wrong, but if someone could let me down gently it would be much appreciated.

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  • Python metaclass to run a class method automatically on derived class

    - by Barry Steyn
    I want to automatically run a class method defined in a base class on any derived class during the creation of the class. For instance: class Base(object): @classmethod def runme(): print "I am being run" def __metclass__(cls,parents,attributes): clsObj = type(cls,parents,attributes) clsObj.runme() return clsObj class Derived(Base): pass: What happens here is that when Base is created, ''runme()'' will fire. But nothing happens when Derived is created. The question is: How can I make ''runme()'' also fire when creating Derived. This is what I have thought so far: If I explicitly set Derived's metclass to Base's, it will work. But I don't want that to happen. I basically want Derived to use the Base's metaclass without me having to explicitly set it so.

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  • private virtual function in derived class

    - by user1706047
    class base { public: virtual void doSomething() = 0; }; class derived : public base { **private:** virtual void doSomething(){cout<<"Derived fn"<<endl;} }; now if i do the following: base *b=new child; b->doSomething(); //it calls the derived class fn even if that is private. Question: 1.its able to call the derived class fn even if that is private.How is it possible? Now if i change the inheritance access specifier from public to protected/private then i get compilation error as "'type cast' : conversion from 'Derived *' to 'base *' exists, but is inaccessible" Notes: I am aware on the concepts of the inheritance access specifiers.So in second case as its derived private/protected, its inaccessible. But here it confuses me for the first question. Any input will be highly appreciated

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  • Calling base class constructor

    - by The Void
    In the program below, is the line Derived(double y): Base(), y_(y) correct/allowed? That is, does it follow ANSI rules? #include <iostream> class Base { public: Base(): x_(0) { std::cout << "Base default constructor called" << std::endl; } Base(int x): x_(x) { std::cout << "Base constructor called with x = " << x << std::endl; } void display() const { std::cout << x_ << std::endl; } protected: int x_; }; class Derived: public Base { public: Derived(): Base(1), y_(1.2) { std::cout << "Derived default constructor called" << std::endl; } Derived(double y): Base(), y_(y) { std::cout << "Derived constructor called with y = " << y << std::endl; } void display() const { std::cout << Base::x_ << ", " << y_ << std::endl; } private: double y_; }; int main() { Base b1; b1.display(); Derived d1; d1.display(); std::cout << std::endl; Base b2(-9); b2.display(); Derived d2(-8.7); d2.display(); return 0; }

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  • Apache2 MPM-prefork MPM-worker multiple instances on same Ubuntu host machine possible?

    - by user60985
    I have a live Apache2/MPM-Worker instance running Django. I want to also run an Apache2/MPM-prefork instance to run some Drupal6 applications on the same host machine and utilize a vast selection of PHP modules that run on the prefork model. I plan to use my MPM-worker instance to reverse proxy to the Apache2-prefork instance for URLS starting with myhost.com/drupal6/. It seems theoretically doable/configurable by having the second Apache2-prefork instance configured to listen on an internal port, say 127.0.0.1:8080 and having my current Apache2-worker configured to proxy pass and reverse pass to it for the 'drupal6' URLs. However, how do I compile or install the apache2-prefork version so it has a different executable name than /usr/sbin/apache2, for example /usr/sbin/apache2p, and so apache2ctl has a different name, say apache2pctl, and that apache2pctl invokes the /usr/sbin/apache2p instead of /usr/sbin/apache2... and so on down the line (eg /etc/apache2p) so I can start and restart my two instances independently? As I understand it, no one executable of 'apache2' can be compiled with both the MPM-prefork and MPM-worker modules, so it seems I need two separate versions of the apache2 MPM flavors. But then I need to invoke and control them by separate names, I assume. I looked at the configuration options for apache2 and I am a bit queasy about compiling a second apache2 version with prefork because I am not sure I can set all the options so that none of my current apache2 files is overwritten. Is there a way? Is there a standard solution to separately installing and controlling prefork and worker apache2 executables on the same machine without them stepping on each other during installation or operation?

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  • How to use instances with s3 load balancing?

    - by Slay
    I have some questions about instances and load balancing in amazon s3. I can configured an instances in s3, but i do not understand how to deal with many instances in s3. Currently, my instance is loaded with mysql, php etc (ALL IN ONE). However how do i ensure my instances is scaling? E.g if i have a site that is suppose to be handled using 3 instances and using amazon rds. Do i need to host my code base in the 3 instances? how do people normally do this? like facebook has 1000+ servers. Do they host their code base in all the 1000+ servers? Thanks

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  • GPL: does one line of GPLed code make program a "derived work"

    - by SigTerm
    I've recently run into some argument with a person that claims to be a lawyer (I have my suspicions about this not being completely true, though). As far as I know, copying even one line of code from GPLed program into proprietary body of code requires you to release the whole thing under GPL, if you ever decide to publish the software and make it available to the public. The person in question claims that it is "absurd" (I know it is, but AFAIK that's how GPL works), it is "redefining the copyright", "GPL has no power to do that", and claiming that "one line of GPLed code makes you release the whole thing under GPL" is absurd. That contradicts the GPL FAQ. Can somebody clarify the situation? Am I right in assumption that copying even smallest subroutine from GPL program into your code automatically makes your program a "derived work" which means you are obliged to release it under GPL license if you publish it?

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  • unity, seeing all instances of same open application windows on all virtual desktop

    - by Nasser M. Abbasi
    I noticed this strange issue with unity. I am using 12.04. The desktop has 4 virtual desktops, which I can switch between using the 'workspace switcher' which is very nice. But I noticed the following: When I have 2 instances of the same app (say 2 different firefox windows, or 2 different terminal windows), in 2 different virtual desktops, then I click on the icon for that application located on the launcher panel (the left long strip with icons on it), then I see the application comes into focus. Then when I click again right away (on the same icon on the launcher), then now all instances of this application that are open come into ONE view (may be on was on desktop 1, and the other was on desktop 3 for example) and then I can now click on the one instance window that I want to select to use. This is all very nice actually. But this does NOT work for all applications! I just tried it, and it worked for firefox, and for gedit and for the gnome terminal. I have one firefox window open in virtual desktop 1, and another window open in virtual desktop 2. I clicked once on the firefox icon, then again, and both windows came into the main desktop and I was able to select which one to use. When I tried the same thing on dolphin file manager, which I also had 2 windows (instances) of it open in 2 different virtual desktops, this behavior did not happen. I clicked again, and nothing happened. Only one remained in focus. So I had to fo look for the second dolphin window the hard way. It looks like some apps are supported by this feature and some are not. How does one make it so that all applications are supported like this? This is a very handy feature. Is it a configuration item somewhere? thanks

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  • Idiomatic Scala way to deal with base vs derived class field names?

    - by Gregor Scheidt
    Consider the following base and derived classes in Scala: abstract class Base( val x : String ) final class Derived( x : String ) extends Base( "Base's " + x ) { override def toString = x } Here, the identifier 'x' of the Derived class parameter overrides the field of the Base class, so invoking toString like this: println( new Derived( "string" ).toString ) returns the Derived value and gives the result "string". So a reference to the 'x' parameter prompts the compiler to automatically generate a field on Derived, which is served up in the call to toString. This is very convenient usually, but leads to a replication of the field (I'm now storing the field on both Base and Derived), which may be undesirable. To avoid this replication, I can rename the Derived class parameter from 'x' to something else, like '_x': abstract class Base( val x : String ) final class Derived( _x : String ) extends Base( "Base's " + _x ) { override def toString = x } Now a call to toString returns "Base's string", which is what I want. Unfortunately, the code now looks somewhat ugly, and using named parameters to initialize the class also becomes less elegant: new Derived( _x = "string" ) There is also a risk of forgetting to give the derived classes' initialization parameters different names and inadvertently referring to the wrong field (undesirable since the Base class might actually hold a different value). Is there a better way? Edit: To clarify, I really only want the Base values; the Derived ones just seem necessary for initializing the Base ones. The example only references them to illustrate the ensuing issues. It might be nice to have a way to suppress automatic field generation if the derived class would otherwise end up hiding a base class field.

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  • Debian/Redmine: Upgrade multiple instances at once

    - by Davey
    I have multiple Redmine instances. Let's call them InstanceA and InstanceB. InstanceA and InstanceB share the same Redmine installation on Debian. Suppose I would want to install Redmine 1.3 on both instances, how would I do that? After upgrading the core files I would have to migrate the databases. What I would like to know is: can I migrate all databases in a single action? Normally I would do something like: rake -s db:migrate RAILS_ENV=production X_DEBIAN_SITEID=InstanceA for each instance, but this would get tedious if you have 50+ instances. Thanks in advance! Edit: The README.Debian file that's in the (Debian) Redmine package states: SUPPORTS SETUP AND UPGRADES OF MULTIPLE DATABASE INSTANCES This redmine package is designed to automatically configure database BUT NOT the web server. The default database instance is called "default". A debconf facility is provided for configuring several redmine instances. Use dpkg-reconfigure to define the instances identifiers. But can't figure out what to do with the "debconf facility". Edit2: My environment is a default Debian 6.0 "Squeeze" installation with a default Redmine (aptitude install redmine) installation on a default libapache2-mod-passenger. I have setup two instances with dpkg-reconfigure redmine.

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  • How to make a derived UITableVIew work

    - by justinhj
    I've made a new class in my Xcode project which is derived from UITableView I then drag a UITableView from in the interface builder onto my view and change the class of the object to my derived class. Then I drag the outlet from the table to the files owner and hook it up to an outlet variable in my main view, which is of the same type as my derived class. How do I also set up the datasource and delegate so that they belong to the derived class?

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  • Can operator<< in derived class call another operator<< in base class in c++?

    - by ivory
    In my code, Manager is derived from Employee and each of them have an operator<< override. class Employee{ protected: int salary; int rank; public: int getSalary()const{return salary;} int getRank()const{return rank;} Employee(int s, int r):salary(s), rank(r){}; }; ostream& operator<< (ostream& out, Employee& e){ out << "Salary: " << e.getSalary() << " Rank: " << e.getRank() << endl; return out; } class Manager: public Employee{ public: Manager(int s, int r): Employee(s, r){}; }; ostream& operator<< (ostream& out, Manager& m){ out << "Manager: "; cout << (Employee)m << endl; //can not compile, how to call function of Employee? return out; } I hoped cout << (Employee)m << endl; would call ostream& operator<< (ostream& out, Employee& e), but it failed.

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  • SQL Server Instancing: Should I use multiple instances or databases?

    - by Spence
    I have a reasonable server connected to a SAN which will be running SQL servers for multiples of the same application. There are no security issues with one application being able to read anothers database. We are unfortunately in 32 bit windows as well. I'm of the opinion that it would be better to use one instance on the server, enable AWE so that the server instance can use almost all of the ram we have and then run each of the databases in the one instance. However I've been overruled by the gods of the IT department on this one, so I'm really curious to hear your thoughts on this. From a performance point of view, am I incorrect that one instance of SQL is better than two? I know that we could do some failover stuff, but doing that on one blade only seems like overkill to me..

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  • Juju instances in aganet-state: down after turning them off (and back on) on EC2

    - by Tyler McAdams
    I turned my Juju instances off on EC2 for a while and after bringing them back online they seem to be in an odd state: [code] claude-vm@claude-vm-fusion:~/Documents/Shell Scripts$ juju status 2012-11-17 17:06:44,094 INFO Connecting to environment... 2012-11-17 17:06:45,590 INFO Connected to environment. machines: 0: agent-state: not-started dns-name: ec2-54-242-142-196.compute-1.amazonaws.com instance-id: i-b0996fcf instance-state: running 1: agent-state: down dns-name: ec2-50-19-186-245.compute-1.amazonaws.com instance-id: i-8c8375f3 instance-state: running 2: agent-state: down dns-name: ec2-54-242-255-238.compute-1.amazonaws.com instance-id: i-56807629 instance-state: running services: wordpress: charm: cs:precise/wordpress-9 exposed: true relations: db: - wordpress-db loadbalancer: - wordpress units: wordpress/0: agent-state: down machine: 2 open-ports: - 80/tcp public-address: ec2-54-242-227-57.compute-1.amazonaws.com wordpress-db: charm: cs:precise/mysql-10 relations: db: - wordpress units: wordpress-db/0: agent-state: down machine: 1 public-address: ec2-54-242-212-177.compute-1.amazonaws.com 2012-11-17 17:06:47,274 INFO 'status' command finished successfully [/code] Can I not take my instances down for a while? Or is this something else?

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  • Connecting multiple ColdFusion 10 instances to a single Apache 2.2 server

    - by Adam Cameron
    This is on Windows 7 Home Premium edition. I have got two ColdFusion 10 (updater 2) instances: "cfusion" (the default one), and "scratch". I have got a single instance of Apache 2.2 running. Within Apache, I have set up two virtual hosts, each of which needs to be served by a different ColdFusion instance. Each of the CF instances serves files fine via Tomcat's internal web server. Apache serves vanilla HTML files fine too. So both CF instances, and both virtual hosts separately work OK. I can get wsconfig.exe to connect either one of the CF instances to the Apache server, and serve CF files via Apache & that instance. However I cannot find a way of connecting the second CF instance to Apache as well, so that both CF instances are conected, each serving one of the virtual hosts. WSConfig doesn't seem to understand the notion of "multiple CF instances", and the changes it makes to the httpd.conf (via mod_jk.conf) does not seem to be implemented in such a way as to accommodate multiple CF instances talking to a single Apache instance, or multiple virtual hosts. I freely admit to not being confident enough with how mod_jk (or even really httpd.conf) works to be able to guess if I can change stuff to make it work. If I try to add the second CF instance using WSConfig, I just get a message "the web server is already configured for ColdFusion". Be that as it may... not the instance of ColdFusion I want to connect it to! If I remove the existing connector to whichever instance is already connected, I can then connect the other one no problems. Not that this helps, but it demonstrates that the CF instance can connect to Apache. This all used to be fairly straight fwd under older versions of CF and JRun :-( The only docs I have found are on the "Connect multiple Apache virtual hosts on a web server to a single ColdFusion server" page, but that specifically only deals with a single CF instance. There is no equivalent page for multiple CF instances. I'm kinda hoping I can move some of the mod_jk config into my virtual host entries in httpd-vhosts.conf (this is how it used to work for JRun), but I've no idea what to put where. I think I've covered all the necessary info here? If not, sing out and I'll add more. Thanks. PS: tried to specifically tag this as "ColdFusion-10" as the answer will be different from previous CF versions, but it won't let me cos my rep on this site is too low (odd how it doesn't consider my rep from other S/O sites...). If someone with sufficient rep can add it, that'd be cool: it's probably a valid tag to have. Ta.

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