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• Dynamic binding in C++

  - by chmike

  I'm implementing a CORBA like server. Each class has remotely callable methods and a dispatch method with two possible input, a string identifying the method or an integer which would be the index of the method in a table. A mapping of the string to the corresponding integer would be implemented by a map. The caller would send the string on the first call and get back the integer with the response so that it simply has to send the integer on subsequent calls. It is just a small optimization. The integer may be assigned dynamically on demand by the server object. The server class may be derived from another class with overridden virtual methods. What could be a simple and general way to define the method binding and the dispatch method ?

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• How can I measure file access performance (and volume) of a (Java) application

  - by stmoebius

  Given an application, how can I measure the amount of data read and written by that application? the time spent reading/writing to disk? The specific application is Java-based (JBoss), and multi-threaded, and running as a service on Windows 7/2008 x64. The overall goal I have is determining whether and why file access is a bottleneck in my application. Therefore, running the application in a defined and repeatable scenario is a given. File access may be local as well as on network shares. Windows performance monitor appears to be too hard to use (unless someone can point me to a helpful explanation). Any ideas?

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• .htaccess: subdomain to sub-folder

  - by Oden

  Hey, How can i redirect a subdomain call to a folder? So when the site, sub.domain.com is requested, the name of the subdomain should point to a subfolder. The server is configured to add every request to the domain, but i get a 404 page everytime i do a non-defined subdomain call (witch is trivial, because theres nothing defined) EDIT my request looks like this: sub.domain.com What and i want to get that it works like a "virtual subdomain", because it has to request a folder with the same name that the subdomain. (domain.com/sub/) So the question is: How to solve this, with .htaccess?

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• How to set -Xbootclasspath for a JRE with a custom launcher?

  - by Tom

  I have a Java application which is using a certain Java Runtime Environment. The application uses it's own launcher to startup the java virtual machine. No use of the java.exe, javaw.exe, javaws.exe binaries is being made -- as the application seems to have it's own launcher which is a different executable. This custom launcher is using the rest of the JRE files, such as bin/client/jvm.dll and rt.jar package etc. Now, the problem is that I want to set a boot class path for this custom launcher. The custom launcher does not support the -Xbootclasspath command line parameter, like the default java.exe does. Is there any way for me to set the boot class path now for this java runtime environment? Thanks in advance. Some things to keep in mind: I do not have the source of this application This is meant for self and personal debugging use only, not for distribution

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• class which cannot be derived

  - by benjamin button

  I found this code here class Usable; class Usable_lock { friend class Usable; private: Usable_lock() {} Usable_lock(const Usable_lock&) {} }; class Usable : public virtual Usable_lock { // ... public: Usable(); Usable(char*); // ... }; Usable a; class DD : public Usable { }; DD dd; // error: DD::DD() cannot access // Usable_lock::Usable_lock(): private member Could anybody explain me this code?

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• Why are C, C++, and LISP so prevalent in embedded devices and robots?

  - by David

  It seems that the software language skills most sought for embedded devices and robots are C, C++, and LISP. Why haven't more recent languages made inroads into these applications? For example, Erlang would seem particularly well-suited to robotic applications, since it makes concurrent programming easier and allows hot swapping of code. Python would seem to be useful, if for no other reason than its support of multiple programming paradigms. I'm even surprised that Java hasn't made a foray into general robotic programming. I'm sure one argument would be, "Some newer languages are interpreted, not compiled" - implying that compiled languages are quicker and use fewer computational resources. Is this still the case, in a time when we can put a Java Virtual Machine on a cell phone or a SunSpot? (and isn't LISP interpreted anyway?)

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• VirtualBox: How to connect to Internet via wi-fi on Mac?

  - by Paul Riedel

  I installed VirtualBox with a Win XP VM on my Mac running OS 10.7.5. My Mac only has a wi-fi connection to the internet. On the settings for the virtual host, I set: Attached to: Bridged Adapter Name: en1: Wi-Fi (AirPort) Adapter Type: Intel PRO/1000 MT Desktop (82540EM) Promiscuous Mode: Deny Mac Address: Cable Connected: true Those are the settings I see around the internet as being correct, but I still can't ping anything. On my Mac I have internet sharing via Ethernet enabled (not sure if that matters). When I start up my WinXP VM, it asks me to install a bunch of hardware which I don't have any drivers to. Do I need to install any ethernet card drivers in order for the internet to work? Thank you!!

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• Does C++ have a proper implementation of interface that does not use vtable?

  - by gilbertc

  Does C++ have a proper implementation of interface that does not use vtable? for example class BaseInterface{ public: virtual void func() const = 0; } class BaseInterfaceImpl:public BaseInterface{ public: void func(){ std::cout<<"called."<<endl; } } BaseInterface* obj = new BaseInterfaceImpl(); obj->func(); the call to func at the last line goes to vtable to find the func ptr of BaseInterfaceImpl::func, but is there any C++ way to do that directly as the BaseInterfaceImpl is not subclassed from any other class besides the pure interface class BaseInterface? Thanks. Gil.

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• Fetch a Rails ActiveRecord 'datetime' attribute as a DateTime object.

  - by Tobias Cohen

  I have an attribute in one of my models that contains a Date/Time value, and is declared using t.datetime :ended_on in my migrations. When I fetch this value using myevent.ended_on, I get a Time object. The problem is that when I try to use this attribute as an axis in a Flotilla chart, it doesn't work properly because Flotilla only recognizes dates as Date or DateTime objects. I thought about writing a virtual attribute that will convert the existing Time value to a DateTime, but I'm wary of doing this, since I've heard that Time can't handle dates later than 2040, and I don't wish to risk creating a "2040 bug" to worry about later. Is there any way I can persuade ActiveRecord to return DateTime objects for this attribute instead of Time objects?

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• Solr adding document cycle & wait on response issue

  - by user1585896

  I am trying to send http post request to Solr for adding 50000 documents (all individual request one after another in while loop). I am using DefaultHttpClient in java to connect to Solr and when I use execute method on my HttpPost Solr takes 3 to 4 ms to response. I have commit=false, autoCommit=false, autoSoftCommit=false. My question is why it takes that much time to response and why cycle it follows to add new document. Basically I want to send add request but do not want to commit to see how many request can Solr handle without doing any kind of commits(without having to do any disk access). My guess is with above parameter tuned off I should be hitting Solr about 10000 times every second, but my result is 300 times a second. I am generating random data to add in my code.

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• Cache images provided through script

  - by Wim Haanstra

  I have a script, which by using several querystring variables provides an image. I am also using URL rewriting within IIS 7.5. So images have an URL like this: http://mydomain/pictures/ajfhajkfhal/44/thumb.jpg or http://mydomain/pictures/ajfhajkfhal/44.jpg This is rewritten to: http://mydomain/Picture.aspx?group=ajfhajkfhal&id=44&thumb=thumb.jpg or http://mydomain/Picture.aspx?group=ajfhajkfhal&id=44 I added caching rules to IIS to cache JPG images when they are requested. This works with my images that are REAL images on the disk. When images are provided through the script, they are somehow always requested through the script, without being cached. The images do not change that often, so if the cache at least is being kept for 30 minutes (or until file change) that would be best. I am using .NET/C# 4.0 for my website. I tried setting several cache options in C#, but I cant seem to find how to cache these images (client-side), while my static images are cached properly.

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• IE6 and IE7 Standalone: What do they render differently?

  - by yar

  It's common knowledge on SO (see this question) that to run IE6 and IE7 you need a Windows box (or virtual box) with only those apps installed. I doubt this is true (they are the real versions, I think). The two browsers I'm interested in are: Standalone IE6 from the MultipleIEs install Standalone IE7 also from Tredosoft (but published elsewhere) These two plus a "real" install of IE8 give you three IE versions in one Windows install. We all know that "You're out of luck if you're trying to run them all reliably in one VM," but can someone please show me JS, CSS, or HTML (or a plugin, etc.) that does not work on the standalone versions as it should? Downvoters: I'm fixing the question so that it's less aggressive, but since there are no comments I don't know what you don't like about this question. Also: I have ALL the test cases set up (IE6, IE7 and IE8, as well as the standalone versions) so if anybody has any code they want me to test, I can do that.

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• Does C++ require a destructor call for each placement new?

  - by Josh Haberman

  I understand that placement new calls are usually matched with explicit calls to the destructor. My question is: if I have no need for a destructor (no code to put there, and no member variables that have destructors) can I safely skip the explicit destructor call? Here is my use case: I want to write C++ bindings for a C API. In the C API many objects are accessible only by pointer. Instead of creating a wrapper object that contains a single pointer (which is wasteful and semantically confusing). I want to use placement new to construct an object at the address of the C object. The C++ object will do nothing in its constructor or destructor, and its methods will do nothing but delegate to the C methods. The C++ object will contain no virtual methods. I have two parts to this question. Is there any reason why this idea will not work in practice on any production compiler? Does this technically violate the C++ language spec?

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• Storing expression template functors

  - by UncaughtException

  Hello guys, at the moment I'm really interested in expression templates and want to code a library for writing and differentiating mathematical functions with a lambda-style syntax. At the moment, I'm able to write (_x * _x)(2); and get the correct result 4. But I would really like to do something like MathFunction f = _x * _x; f(2);, but I don't have any ideas on how to cope with the recursive expression templates on the right side. Is it possible to achieve this without using the 'auto'-Keyword instead of MathFunction or having to make the operator() virtual? Thanks for your help!

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• Handler not yet determined error

  - by SourceC

  Hello, I don’t know anything about deploying a website, so I probably made some stupid mistake. Anyways, I opened IIS 7 manager, created new virtual directory ( via Add Application ) and pointed it to physical directory where Visual studio saved my Web project. But when I tried to request an .aspx page, browser reported the following error (I won’t post the whole error, but just the interesting bits): Handler: Not yet determined Config Error: Cannot read configuration file due to insufficient permissions Logon User: Not yet determined A) why is handler not yet determined? As far as I know, IIS7 does have Asp.Net handler registered?! B) Why wouldn’t IIS have sufficient permissions? Does that mean I should give IIS higher privileges? Or does Asp.Net runtime have insufficient permissions? C) Could the error also be due to the fact that perhaps it expected the user to authenticate itself? I’m assuming this due to Logon user not yet being determined? D) And finally, any ideas how to make it work? thanx

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• java cannot reserver heap size error on windows server

  - by Prad

  HI, I have the following configuration: Server : windows 2003 server (32 bit) java version: 1.5_0_22 I get the following error when executing from command line ( my code is based off eclipse wihch gives the same error) java -XX:MaxPermSize=256m -Xmx512m Error occurred during initialization of VM Could not reserve enough space for object heap Could not create the Java virtual machine. The server has over 20GB physical memory with over 19 GB free right now. It does not give an error upto -Xmx486m I have read other articles about contiguous memory space. There is hardly anything running on this server. Can I validae this in any way? Thanks

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• Visual C++ 9 Linker file size limitation.

  - by Raindog

  It appears that the visual C++ 9 linker has a file allocation algorithm that doubles the size of the file every allocation, so you get 512mb, 1024mb, 2048mb, 4096mb. The problem is that it is using a library that cannot handle files larger 2048MB, and as such crashes with an error such as "cannot read file at is the disk full or write protected". Is there a way to bypass this limitation or otherwise replace the linker with something else that works? A bit of background, I have a code generator that generates a large number of files, ~15k cpp files, I've managed to reduce the number of files to something about 6k to get something that at least completes the linking process, I would like to be able to include all 15k without having to create multiple libs.

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• Need a Concatenating VBA code to prevent memory issue workaround

  - by doharr

  My set up: Have 50,000 rows of data. ( My row count will increase in the future. So might as well say I have a full worksheet of 64000+ rows.) All Data is TEXT, no formulas, etc. Column A is open Columns B thru AC contain the Data that needs to be concatenated The Data in the rows once concatenated to Column A will contain 60,000 digits or 6kb in file size. After additional maniuplation each cell will become a file. I have tried concatenating in Excel and I run into memory issues. The memory issue is when I Select and fill down the concatenating function into the worksheet. It crashes at the 8200 +/-row. My system is 2gb of ram, windows xp professional and Excel 2003. Have 4GB of disk space Hoping to find a VBA code that will conserve memory, and not crash like it does in excel. Thank you

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• CLR - Common language runtime detected an invalid program in VS.NET

  - by Jimmy

  I have been using Visual Studio 2008 quite long but lately I am getting this message when I am developing an application in C#: Common language runtime detected an invalid program This happens when I try to enter to the properties of a component (text masked box properties, tool box property etc..). But it really became a problem when I tried to launch an other solution that I downloaded from the Developer's 5 star program of Microsoft and it didn't allowed me to launch at all and just got the same problem... I looked for the answer at google but just got some clues about people having the same vague error but in different situations like in ASP.NET I would appreciate any help with this issue... :( I do not want to reinstall VS, that will be my last resource... Update: I never figured out what the problem was so I installed a virtual machine with Windows XP on it, there I only have Visual Studio and Netbeans.

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• Where does the compiler store methods for C++ classes?

  - by Mashmagar

  This is more a curiosity than anything else... Suppose I have a C++ class Kitty as follows: class Kitty { void Meow() { //Do stuff } } Does the compiler place the code for Meow() in every instance of Kitty? Obviously repeating the same code everywhere requires more memory. But on the other hand, branching to a relative location in nearby memory requires fewer assembly instructions than branching to an absolute location in memory on modern processors, so this is potentially faster. I suppose this is an implementation detail, so different compilers may perform differently. Keep in mind, I'm not considering static or virtual methods here.

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• Passing control's ID to javascript via ScriptControlDescriptor

  - by markiz

  I create a control in CreateChildControls(): HtmlGenericControl mycontrol= HtmlGenericControl("li"); mycontrol.ID = "controlID"; controlId = mycontrol.ID; protected virtual IEnumerable<ScriptDescriptor> GetScriptDescriptors() { ScriptControlDescriptor descriptor = new ScriptControlDescriptor("Project.TEditor", this.ClientID); descriptor.AddProperty("controlId", controlId); return new ScriptDescriptor[] { descriptor }; } Then in javascript i try to find this control using the ID property: alert($get(this.get_controlId())); I get null because the actual control ID has a prefix that was added by asp. How to solve that?

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• Print an EObject ?

  - by tul

  I am writing some eclipse emf code and would like to print the content of an EObject (not store it to disk). Here is what I try: public static void print(EObject obj) { Resource eResource = obj.eResource(); try { eResource.save(System.out, null); } catch (IOException e) { e.printStackTrace(); } } but that gives a NullPointerException. I have tried this instead: public static void print(EObject obj) { ResourceSet resourceSet = new ResourceSetImpl(); resourceSet.getResourceFactoryRegistry().getProtocolToFactoryMap() .put("*", new XMIResourceFactoryImpl()); Resource resource = resourceSet.createResource(URI.createURI("dummyfile.xml")); resource.getContents().add(obj); try { resource.save(System.out, null); } catch (IOException ioe) { ioe.printStackTrace(); } } This works, but is it not possible to print to screen without specifying a dummy URI??

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• c++ polymorphism and other function question

  - by aharont

  i have got this code: class father{ public: virtual void f() { cout<<1;} }; class son:public father{ public: void f() {cout<<2;} }; void test (father x){x.f();} int main(){ son s; test(s); } the question says: the output is '1', what is the rule about polymorphism that the programmer forgot and how can i fix it so the output would be '2'? there is another rule that the programmer forgot when he wrote the father class, and he need to add an empty function to avoid problems from other sons of the father class. what is the rule and what is the missing function? another question write the g function so the next code would run with no crashes int x=11; g(x)=22;

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• Why Is It That Generics Constraint Can't Be Casted to Its Derived Type?

  - by Ngu Soon Hui

  It is quite puzzling to find out that Generics Constraint Can't Be Casted to Its Derived Type. Let's say I have the following code: public abstract class BaseClass { public int Version { get { return 1; } } public string FixString { get; set; } public BaseClass() { FixString = "hello"; } public virtual int GetBaseVersion() { return Version; } } public class DeriveClass: BaseClass { public new int Version { get { return 2; } } } And guess what, this method will return a compilation error: public void FreeConversion<T>(T baseClass) { var derivedMe = (DeriveClass)baseClass; } I would have to cast the baseClass to object first before I can cast it to DerivedClass. Seems to me pretty ugly. Why this is so?

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• Does a Perl module know where it is installed?

  - by CoffeeMonster

  Hi Perl programmers, I have started creating a Perl package that contains a default email template. The MANIFEST looks something like: SendMyEmail.pm SendMyEmail/defualt_email.tt Currently I know where the module (and the template) are - but does the module itself know where on disk it is? So could the module find the default template without my help? # This is what I would like to do. package SendMyEmail; sub new { my ($self, $template) = @_; $template ||= $dir_of_SendMyEmail .'/SendMyEmail/default_email.tt'; # ?? } Is there a better way of including a templates text, or a better place to put the template? Any references to CPAN modules that do something similar would be welcome. Thanks in advance.

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