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• Alternative to c++ static virtual methods

  - by Jaime Pardos

  In C++ is not possible to declare a static virtual function, neither cast a non-static function to a C style function pointer. Now, I have a plain ol' C SDK that uses function pointers heavily. I have to fill a structure with several function pointers. I was planning to use an abstract class with a bunch of static pure virtual methods, and redefine them in derived classes and fill the structure with them. It wasn't until then that I realized that static virtual are not allowed in C++. Is there any good alternative? The best I can think of is defining some pure virtual methods GetFuncA(), GetFuncB(),... and some static members FuncA()/FuncB() in each derived class, which would be returned by the GetFuncX(). Then a function in the abstract class would call those functions to get the pointers and fill the structure.

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• Initialize virtual attributes

  - by Horace Loeb

  I have an IncomingEmail model with an attachments virtual attribute: class IncomingEmail < ActiveRecord::Base attr_accessor :attachments end I want the attachments virtual attribute to be initialized to [] rather than nil so that I can do: >> i = IncomingEmail.new => #<IncomingEmail id: nil,...) >> i.attachments << "whatever" Without first setting i.attachments to [] (put another way, I want this virtual attribute to default to an empty array rather than nil)

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• Virtual member call in a constructor when assigning value to property

  - by comecme

  I have an Abstract class and a Derived class. The abstract class defines an abstract property named Message. In the derived class, the property is implemented by overriding the abstract property. The constructor of the derived class takes a string argument and assigns it to its Message property. In Resharper, this assignment leads to a warning "Virtual member call in constructor". The AbstractClass has this definition: public abstract class AbstractClass { public abstract string Message { get; set; } protected AbstractClass() { } public abstract void PrintMessage(); } And the DerivedClass is as follows: using System; public class DerivedClass : AbstractClass { private string _message; public override string Message { get { return _message; } set { _message = value; } } public DerivedClass(string message) { Message = message; // Warning: Virtual member call in a constructor } public DerivedClass() : this("Default DerivedClass message") {} public override void PrintMessage() { Console.WriteLine("DerivedClass PrintMessage(): " + Message); } } I did find some other questions about this warning, but in those situations there is an actual call to a method. For instance, in this question, the answer by Matt Howels contains some sample code. I'll repeat it here for easy reference. class Parent { public Parent() { DoSomething(); } protected virtual void DoSomething() {}; } class Child : Parent { private string foo; public Child() { foo = "HELLO"; } protected override void DoSomething() { Console.WriteLine(foo.ToLower()); } } Matt doesn't describe on what error the warning would appear, but I'm assuming it will be on the call to DoSomething in the Parent constructor. In this example, I understand what is meant by a virtual member being called. The member call occurs in the base class, in which only a virtual method exists. In my situation however, I don't see why assigning a value to Message would be calling a virtual member. Both the call to and the implementation of the Message property are defined in the derived class. Although I can get rid of the error by making my Derived Class sealed, I would like to understand why this situation is resulting in the warning.

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• Performance problem Loading Dataset inside a virtual.

  - by ShaneH

  Host Configuration: HP EliteBook 8530w 4G Ram Win7 Ultimate 64Bit RC SQL Server 2005 64bit Developer Edition Virtual: Windows Virtual PC 1G Ram allocated Integration Services installed Windows XP 64bit Up to date service packs and .Net framework through 3.5 SP1 Sharing the Gigabit network adapter of the Host I have a simple .Net console application which loads a dataset of approximately 37K rows. Running the application on the host executes in approximately 4 seconds. Running inside the virtual takes 729 seconds. The size of the application grows to about 65Mb when the dataset is finished loading, no calculated columns or event handlers are attached. [edit] I changed the virtual to use a loopback adapter to communicate with the host and performance is now on par with running on hardware. Any ideas as to why it would going over the network adapter be almost 200x longer? TraceRt shows that the connection is only one hop. Thanks, Shane Holder

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• VSC++, virtual method at bad adress, curious bug

  - by antoon.groenewoud

  Hello, This guy: virtual phTreeClass* GetTreeClass() const { return (phTreeClass*)m_entity_class; } When called, crashed the program with an access violation, even after a full recompile. All member functions and virtual member functions had correct memory adresses (I hovered mouse over the methods in debug mode), but this function had a bad memory adress: 0xfffffffc. Everything looked okay: the 'this' pointer, and everything works fine up until this function call. This function is also pretty old and I didn't change it for a long time. The problem just suddenly popped up after some work, which I commented all out to see what was doing it, without any success. So I removed the virtual, compiled, and it works fine. I add virtual, compiled, and it still works fine! I basically changed nothing, and remember that I did do a full recompile earlier, and still had the error back then. I wasn't able to reproduce the problem. But now it is back. I didn't change anything. Removing virtual fixes the problem. Sincerely, Antoon

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• virtual methods and template classes

  - by soxs060389

  Hi I got over a problem, I think a very specific one. I've got 2 classes, a B aseclass and a D erived class (from B aseclass). B is a template class ( or class template) and has a pure virtual method virutal void work(const T &dummy) = 0; The D erived class is supposed to reimplement this, but as D is Derived from B rather than D being another template class, the compiler spits at me that virtual functions and templates don't work at once. Any ideas how to acomplish what I want? I am thankfull for any thoughts and Ideas, especially if you allready worked out that problem this class is fixed aka AS IS, I can not edit this without breaking existing code base template <typename T> class B { public: ... virtual void work(const T &dummy) = 0; .. }; take int* as an example class D : public B<int*>{ ... virtual void work(const int* &dummy){ /* put work code here */ } .. }; Edit: The compiler tells me, that void B<T>::work(const T&) [with T = int*] is pure virtual within D

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• virtual function call from base class

  - by Gal Goldman

  Say we have: Class Base { virtual void f(){g();}; virtual void g(){//Do some Base related code;} }; Class Derived : public Base { virtual void f(){Base::f();}; virtual void g(){//Do some Derived related code}; }; int main() { Base *pBase = new Derived; pBase-f(); return 0; } Which g() will be called from Base::f()? Base::g() or Derived::g()? Thanks...

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• most interesting cases of using inheritance in web programming?

  - by medusa

  when did you use inheritance in a web project in a very interesting way

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• Template Child Class Overriding a Parent Class's Virtual Function

  - by user334066

  The below code compiles with gcc v4.3.3 and the templated child class seems to be overriding a virtual function in the parent, but doesn't that break the rule that you cannot have a virtual template function? Or is something else happening that I don't understand? class BaseClass { public: virtual void Func(int var) { std::cout<<"Base int "<<var<<std::endl; } virtual void Func(double var) { std::cout<<"Base double "<<var<<std::endl; } }; template <class TT> class TemplateClass : public BaseClass { public: using BaseClass::Func; virtual void Func(TT var) { std::cout<<"Child TT "<<var<<std::endl; } }; int main(int argc, char **argv) { BaseClass a; TemplateClass<int> b; BaseClass *c = new TemplateClass<int>; int intVar = 3; double doubleVar = 5.5; a.Func(intVar); a.Func(doubleVar); b.Func(intVar); b.Func(doubleVar); c->Func(intVar); c->Func(doubleVar); delete c; } This then outputs: Base int 3 Base double 5.5 Child TT 3 Base double 5.5 Child TT 3 Base double 5.5 as I hoped, but I'm not sure why it works.

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• Instance where embedded C++ compilers don't support multiple inheritance?

  - by Nathan

  I read a bit about a previous attempt to make a C++ standard for embedded platforms where they specifically said multiple inheritance was bad and thus not supported. From what I understand, this was never implemented as a mainstream thing and most embedded C++ compilers support most standard C++ constructs. Are there cases where a compiler on a current embedded platform (i.e. something not more than a few years old) absolutely does not support multiple inheritance? I don't really want to do multiple inheritance in a sense where I have a child with two full implementations of a class. What I am most interested in is inheriting from a single implementation of a class and then also inheriting one or more pure virtual classes as interfaces only. This is roughly equivalent to Java/.Net where I can extend only one class but implement as many interfaces as I need. In C++ this is all done through multiple inheritance rather than being able to specifically define an interface and declare a class implements it.

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• Virtual PC (XPMode) - How to access Webserver on guest from host

  - by sannoble

  I have Windows XP running inside Windows 7 via Virtual PC (XPMode) and installed Zend Server CE on the virtual XP guest. The webserver is running and can be accessed on the guest, but I cannot access the webserver from the Win7 host. I configured a static IP address and subnet of 255.255.255.0 on the guest and can ping this IP from the guest but not from the host. The other way it works fine, i.e. I can ping the host from the guest. I can also access the internet from the virtual XP guest. I tried different Network Options in the VirtualPC settings, but nothing helps. Googling the topic I couldn't find anything helpful yet. Any idea, what I could try to access the webserver on the virtual XP guest from the Win7 host?

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• C++ static virtual members?

  - by cvb

  Is it possible in C++ to have a member function that is both static and virtual? Apperantly, there isn't a straight-forward way to do it (static virtual member(); is a complie error), but at least a way to acheive the same effect? I.E: struct Object { struct TypeInformation; static virtual const TypeInformation &GetTypeInformation() const; }; struct SomeObject : public Object { static virtual const TypeInformation &GetTypeInformation() const; }; It makes sence to use GetTypeInformation() both on an instance (object->GetTypeInformation()) and on a class (SomeObject::GetTypeInformation()), which can be useful for comparsions and vital for templates. The only ways I can think of involves writing two functions / a function and a constant, per class, or use macros. Any other solutions?

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• need a virtual template member workaround

  - by yurib

  Hello, I need to write a program implementing the visitor design pattern. The problem is that the base visitor class is a template class. This means that BaseVisited::accept() takes a template class as a parameter and since it uses 'this' and i need 'this' to point to the correct runtime instance of the object, it also needs to be virtual. I'd like to know if there's any way around this problem. template <typename T> class BaseVisitor { public: BaseVisitor(); T visit(BaseVisited *visited); virtual ~BaseVisitor(); } class BaseVisited { BaseVisited(); template <typename T> virtual void accept(BaseVisitor<T> *visitor) { visitor->visit(this); }; // problem virtual ~BaseVisited(); }

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• Ubuntu virtual memory caches suck up memory

  - by Tom

  Hey all, I've got an Ubuntu 9.10 64-bit server that seems to use up all available memory. According to my munin graphs, almost all of the memory used up is in the swap cache, cache, and slab cache. (I take this to mean virtual memory caches, am I right in assuming this?) Once memory usage approaches 100%, some (although not all) system services such as SSH become sluggish and unresponsive. After rebooting the system, performance and memory usage become normal for a time. Some interesting tidbits: The system runs Apache 2, MySQL, Munin, and sshd. The memory usage spikes happen at the same time every night (at 10 PM sharp.) There appears to be nothing in the crontab for any of the users, and nothing in /etc/cron.d/* out of the ordinary, let alone something that would occur at 10 PM. My question is, how do I figure out what is causing the memory suckage? I've tried the usual utilities (e.g. ps, top, etc) but I can't seem to find anything unusual. Any ideas? Thanks in advance!

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• URL Rewriting on GoDaddy Virtual Server

  - by Aristotle

  I migrated a Kohana2 application from a shared-hosting environment over to a virtual dedicated server. After this migration, I can't seem to get my .htaccess file working again. I apologize up front, but over the years I have never experienced so much frustration with anything else as I do with the dreaded .htaccess file. Presently I have my project installed immediately within a directory in my public folder: /var/html/www/info.php (general information about server) /var/html/www/logo.jpg (some flat file) /var/html/www/somesite.com/[kohana site exists here] So my .htaccess file is within that directory, and has the following contents: # Turn on URL rewriting RewriteEngine On # Installation directory RewriteBase /somesite.com/ # Protect application and system files from being viewed # This is only necessary when these files are inside the webserver document root RewriteRule ^(application|modules|system) - [R=404,L] # Allow any files or directories that exist to be displayed directly RewriteCond %{REQUEST_FILENAME} !-f RewriteCond %{REQUEST_FILENAME} !-d # Rewrite all other URLs to index.php/URL RewriteRule .* index.php?kohana_uri=$0 [PT,QSA,L] # Alternativly, if the rewrite rule above does not work try this instead: #RewriteRule .* index.php?kohana_uri=$0 [PT,QSA,L] This doesn't work. The initial controller is loaded, since index.php is called up implicitly when nothing else is in the url. But if I try to load up some other non-default controller, the site fails. If I place the index.php back within the url, the call to other controllers works just fine. I'm really at my wits end, and would appreciate some direction here.

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• VMWare Fusion: "No Permission to access this virtual machine"

  - by Craig Walker

  I had a VMWare Fusion VM backed up on my home network file server (Ubuntu). I wanted to run it again, so I copied it back to my Macbook. When I tried to launch it in VMWare, I got an error message: No permission to access this virtual machine. Configuration file: /Users/craig/WinXP Clean + Scanner.vmwarevm/WinXP Pro Test.vmx The permissions look fine to me: The bundle directory is 777 The bundle files (including the listed .vmx) are all 666 User is craig (my current user); group is staff. I changed the group to wheel at the suggestion of this page, but that didn't help. Finder shows read & write for craig, staff, and everyone on the bundle directory The bundle dir is also not locked Finder also shows rw and unlocked for the .vmx file The parent directory is also rw & unlocked Disk Utility permissions check doesn't show any problems with any of the associated files It sure looks like I should have wide open access to run this VM; why is Fusion complaining?

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• Physical-to-virtual for personal use

  - by Journeyman Geek

  One of my current projects involves reducing the number of old computers lying around. So far, the office systems have been downsized from 5 to 2. One system which had no data on it was dumped entirely, while three other identical boxes were consolidated into to one (I swap hard drives as needed and they just work(tm)). I want to make further cuts. The physical systems in question all run windows xp sp3, and were old Pentium 4s with 256 MB of RAM. Currently, I have got a VirtualBox running on another system. My intention is to migrate all services to that. We can assume that disk space and RAM on the host is not an issue. I'd rather not go with a client-server physical-to-virtual (P2V) method like what VirtualBox uses now. I have a few specific concerns as well - specifically whether I'd need to reactivate or sysprep for dissimilar hardware first. An offline tool for imaging (Windows or Linux) would not be an issue since the drives could be mounted onto another system I have anyway or I could use a LiveCD. What would be my options for P2V conversion, and what would I need to keep in mind when doing this?

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• No LPT port in Windows 7 virtual machines

  - by KeyboardMonkey

  Windows 7 has MS virtual PC integrated, the VM settings don't give a parallel LPT port mapping to the physical machine. Where did it go? Has anyone else noticed this, and found a solution? Update: After much digging, I found the one and only reference to this issue, on the VPC Blog: "Parallel port devices are not supported, as they are relatively rare today." -More details- It's a XP VM I've been using since VPC 2007 days, which did have this functionality. This is to configure barcode printers via the LPT port. Since the (new) MS VM can't map to my physical LPT port, I'm having a hard time configuring printers. My physical ports are enabled in the BIOS. It has worked the past 3 years, before switching to Win 7. Any help is appreciated. This screen shot of the VM settings shows COM ports, but LPT is no more In contrast, here is a screen shot of VPC 2007 (before it got integrated into Win 7). Notice how it has LPT support

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• Virtual machines with failover setup

  - by kimmmo

  We have three servers and our plan is to run a number of virtual machines on them in such manner, that if one of the nodes blow up, we can either quickly or seamlessly get a spare running on another node. In addition to the normal networking, they're interconnected via dual 10Gbit NIC's, so networked raid/mirroring shouldn't be a problem. The guest VM's are mostly going to be running text mode linux, but of course it wouldn't hurt to be able to spin up a non-mission critical windows guest for running Visual Studio or checking IE compatibility of a web app. We've spent some time trying to get some magical cloud setup running using Stackops and Crowbar but it started to look like they were offering way too much and were too complicated for our needs. The next candidate, I think, is Ubuntu 11.04 server + KVM + Ganeti + Drbd, unless you can come up with a suggestion for a better solution that we have missed. Requirements: Installation should be simple or at least understandable without being in the dev team A browser interface for creating and managing VM's is a nice bonus Single node's hardware failure should cause minimal downtime for VM's that were running on that node Adding more nodes should be possible without shutting down the VM's.

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• Authenticate domain-user credentials on unjoined virtual machine?

  - by bwerks

  Hi all, This question may sound silly, and perhaps a bit insane, but--is there any way to run a process on a machine not joined to a domain using credentials from a user in that domain? In my case, I'm running virtual machines installed with release binaries from our build process, as well as Visual Studio. Visual Studio is there to debug our release binaries, however it's being executed with vm-local user credentials. This means that it can't authenticate to our TFS deployment when executing "tf.exe view" to utilize our Source Server for debugging. Team Explorer manages to authenticate to TFS using a UI prompt, however I suspect that it's because we supply it with the TFS deployment's URI, and it's designed to display a prompt to facilitate workgroup scenarios; i.e. it's not like we're getting it for free. My instincts tell me the only way to authenticate on this vm is to join it or somehow form a one-way trust or something, but is there an easier way? For automation we're going to want to script this eventually, but I'm first surveying the feasibility of the thing.

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• Missing access log for virtual host on Plesk

  - by Cummander Checkov

  For some reason i don't understand, after creating a new virtual host / domain in Plesk a few months back, i cannot seem to find the access log. I noticed this when running /usr/local/psa/admin/sbin/statistics The host in question is being scanned Main HTML page is 'awstats.<hostname_masked>-http.html'. Create/Update database for config "/opt/psa/etc/awstats/awstats.<hostname_masked>.com-https.conf" by AWStats version 6.95 (build 1.943) From data in log file "-"... Phase 1 : First bypass old records, searching new record... Searching new records from beginning of log file... Jumped lines in file: 0 Parsed lines in file: 0 Found 0 dropped records, Found 0 corrupted records, Found 0 old records, Found 0 new qualified records. So basically no access logs have been parsed/found. I then went on to check if i could find the log myself. I looked in /var/www/vhosts/<hostname_masked>.com/statistics/logs but all i find is error_log Does anybody know what is wrong here and perhaps how i could fix this? Note: in the <hostname_masked>.com/conf/ folder i keep a custom vhost.conf file, which however contains only some rewrite conditions plus a directory statement that contains php_admin_flag and php_admin_value settings. None of them are related to logging though.

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• backup an existing linux server to a virtualbox virtual machine

  - by user146526

  I have some servers and VPSs to many companies across the world. I want to back them up locally. I have some backup solutions enabled to remote hosts, but I want to have a local backup on a computer at home. What I am thinking is: 1) Create a virtualbox virtual machine, install the same version linux as the server. 2) Use rsync to backup the server to the local virtualbox machine. (something like rsync -av --delete --progress --exclude '/dev/' --exclude '/proc/' root@server_ip:// / ) 3) Repeat the command every few days update files. 4) In case of a hard disk failure, or any other bad event, reverse the rsync command and get the files back and continue my bussiness. I tried it with 2 openvz VPS, the one was a backup of the other. I also tried to transfer normal linux server host to openvz machine and it worked great. That way looks pretty clean and easy to me, this is the kind of solution I am looking for. However I need to be sure that this will work if I am going to do it. The question is, will that work ok ? Does anyone see any problem with that ? Do you have any other suggestions ? Thanks

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• Dedicated Mouse and Keyboard on Virtual Box VM

  - by Myersguy

  To all super users, Currently I am trying to run virtual box on my second monitor, with a dedicated mouse and keyboard. However, doing so has not proven easy. There has been times where the mouse works, but not the keyboard, vice versa, or nothing works at all. The biggest problem I am running into is this: When enabling the USB mouse and keyboard from the VM, I get an error: 'USB Device is busy with a previous request.' The only thing that is using second mouse and keyboard, however, is Windows. The other error I have received stated that the VM was unable to create a proxy for the device. Additionally, the VM occasionally will disable the secondary keyboard entirely, requiring me to unplug and replug it into my PC to re-enable it again. Keyboard auto-capture is disabled, and while a solution I was reading online stated to turn off mouse integration, that option is grayed out on my machine. Any help would be appreciated. Thanks. /firstquestion.

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• How to create a Windows Server 2008 VM

  - by Gauls

  Hi. I have Windows 2008 Server set up. I want to create a Virtual machine with O/S Windows 2008 Server which can be booted with VM player. How do i go about it? Thanks, gauls

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• How to creare Windows server 2008 VM

  - by Gauls

  Hi I have windows 2008 server setup. Want to create a Virtual machine with O/S windows 2008 server which can be booted with VM player how do i go about it? Thanks, gauls

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