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  • Advantages of Singleton Class over Static Class?

    Point 1) Singleton We can get the object of singleton and then pass to other methods. Static Class We can not pass static class to other methods as we pass objects Point 2) Singleton In future, it is easy to change the logic of of creating objects to some pooling mechanism. Static Class Very difficult to implement some pooling logic in case of static class. We would need to make that class as non-static and then make all the methods non-static methods, So entire your code needs to be changed. Point3:) Singleton Can Singletone class be inherited to subclass? Singleton class does not say any restriction of Inheritence. So we should be able to do this as long as subclass is also inheritence.There's nothing fundamentally wrong with subclassing a class that is intended to be a singleton. There are many reasons you might want to do it. and there are many ways to accomplish it. It depends on language you use. Static Class We can not inherit Static class to another Static class in C#. Think about it this way: you access static members via type name, like this: MyStaticType.MyStaticMember(); Were you to inherit from that class, you would have to access it via the new type name: MyNewType.MyStaticMember(); Thus, the new item bears no relationships to the original when used in code. There would be no way to take advantage of any inheritance relationship for things like polymorphism. span.fullpost {display:none;}

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  • set static member pointer variables

    - by Chris
    I'm trying to set a static pointer variable in a class but I'm getting these errors for each variable I try to set. error C4430: missing type specifier - int assumed. Note: C++ does not support default-int error C2040: 'xscroll' : 'int' differs in levels of indirection from 'float *' error C2440: 'initializing' : cannot convert from 'float **' to 'int' Here is the code Enemy.h #include <windows.h> #include "Player.h" class Enemy { public: Enemy(float xPos, float yPos); Enemy(void); ~Enemy(void); //update the position of the user controlled object. void updatePosition(float timeFactor); //loads all the enemy textures void static loadTextures(); //creates a set number of enemies void static createEnemies(int numEnemies, Enemy * enemyArray); GLuint static enemyTex; static float * xscroll; static float * yscroll; static Player * player; private: bool checkCollison(float x, float y, int radius); float XPos; float YPos; }; trying to set variables Enemy::xscroll = &xscroll; Enemy::yscroll = &yscroll; Enemy::player = &player;

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  • Java: Initializing a public static field in superclass that needs a different value in every subclas

    - by BinaryMuse
    Good evening, I am developing a set of Java classes so that a container class Box contains a List of a contained class Widget. A Widget needs to be able to specify relationships with other Widgets. I figured a good way to do this would be to do something like this: public abstract class Widget { public static class WidgetID { // implementation stolen from Google's GWT private static int nextHashCode; private final int index; public WidgetID() { index = ++nextHashCode; } public final int hashCode() { return index; } } public abstract WidgetID getWidgetID(); } so sublcasses of Widget could: public class BlueWidget extends Widget { public static final WidgetID WIDGETID = new WidgetID(); @Override public WidgetID getWidgetID() { return WIDGETID; } } Now, BlueWidget can do getBox().addWidgetRelationship(RelationshipTypes.SomeType, RedWidget.WIDGETID, and Box can iterate through it's list comparing the second parameter to iter.next().getWidgetID(). Now, all this works great so far. What I'm trying to do is keep from having to declare the public static final WidgetID WIDGETID in all the subclasses and implement it instead in the parent Widget class. The problem is, if I move that line of code into Widget, then every instance of a subclass of Widget appears to get the same static final WidgetID for their Subclassname.WIDGETID. However, making it non-static means I can no longer even call Subclassname.WIDGETID. So: how do I create a static WidgetID in the parent Widget class while ensuring it is different for every instance of Widget and subclasses of Widget? Or am I using the wrong tool for the job here? Thanks!

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  • Static member function pointer to hold non static member function

    - by user1425406
    This has defeated me. I want to have a static class variable which is a pointer to a (non-static) member function. I've tried all sorts of ways, but with no luck (including using typedefs, which just seemed to give me a different set of errors). In the code below I have the static class function pointer funcptr, and I can call it successfully from outside the class, but not from within the member function CallFuncptr - which is what I want to do. Any suggestions? #include <stdio.h> class A { public: static int (A::*funcptr)(); int Four() { return 4;}; int CallFuncptr() { return (this->*funcptr)(); } // doesn't link - undefined reference to `A::funcptr' }; int (A::*funcptr)() = &A::Four; int main() { A fred; printf("four? %d\n", (fred.*funcptr)()); // This works printf("four? %d\n", fred.CallFuncptr()); // But this is the way I want to call it }

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  • c# object initializer complexity. best practice

    - by Andrew Florko
    I was too excited when object initializer appeared in C#. MyClass a = new MyClass(); a.Field1 = Value1; a.Field2 = Value2; can be rewritten shorter: MyClass a = new MyClass { Field1 = Value1, Field2 = Value2 } Object initializer code is more obvious but when properties number come to dozen and some of the assignment deals with nullable values it's hard to debug where the "null reference error" is. Studio shows the whole object initializer as error point. Nowadays I use object initializer for straightforward assignment only for error-free properties. How do you use object initializer for complex assignment or it's a bad practice to use dozen of assigments at all? Thank you in advance!

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  • Static vs Non Static constructors

    - by Neil N
    I can't think of any reasons why one is better than the other. Compare these two implementations: public class MyClass { public myClass(string fileName) { // some code... } } as opposed to: public class MyClass { private myClass(){} public static Create(string fileName) { // some code... } } There are some places in the .Net framework that use the static method to create instances. At first I was thinking, it registers it's instances to keep track of them, but regular constructors could do the same thing through the use of private static variables. What is the reasoning behind this style?

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  • Calling a static Func from a static class using reflection

    - by ChrisO
    Given the static class: public static class Converters { public static Func<Int64, string> Gold = c => String.Format("{0}g {1}s {2}c", c/10000, c/100%100, c%100); } I am receiving the Func name from a database as a string (regEx.Converter). How can I invoke the Gold Func using reflection? Here is what I have so far: var converter = typeof(Converters).GetMember(regEx.Converter); if (converter.Count() != 0) { //throw new ConverterNotFoundException; } matchedValue = converter.Invoke(null, new object[]{matchedValue}) as string;

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  • two static libraries

    - by user295030
    Hi, I am currently providing a static library using vs2008. I am in the process of building my static library. However, since I am using another static library is there a way that then i package this as a single library. The reason here is that they will be calling functions in my library that depend on that other static library (.lib). I am not sure how to go about doing that and needs some help with that.

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  • Is it possible to call a non-static function inside static function in C#?

    - by djzmo
    Is it possible to call a non-static function that uses a public non-static class inside a static function in C#? public class MyProgram { private Thread thd = new Thread(myStaticFunction); public AnotherClass myAnotherClass = new AnotherClass(); public MyProgram() { thd.Start(); } public static void myStaticFunction() { myNonStaticFunction(); } private void myNonStaticFunction() { myAnotherClass.DoSomethingGood(); } } Well, the invalid code like above is what I need. Any idea?

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  • Rails image_tag prefix to a static content

    - by pepernik
    I would like to server all static content from a different domain like static.mydomain.com. Is there an option every image_tag, javascript_include_tag and stylesheet_link_tag would automatically add a prefix to that static domain? Example: image_tag '/images/img1.png' would generate http://static.mydomain.com/images/img1.png Thx10x.

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  • static library, but I still need headers?

    - by ML
    Hi All, I have a bunch of projects that all could share a "common" static library of classes. What confuses me is if I make a static library out of these classes and link against it in my projects that I still need the headers of the classes in the static library in my main projects. What is the benefit of the static library then? How do companies like Adobe deal with this?

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  • apache2 mod_deflate static content

    - by rizen
    I have a server serving up a JS file a few million times a day using apache2. Some of my users would like the JS to be gzipped. Does anyone know how apache2 mod_deflate handles compression of static files? Will it compress the js for each request(in which case I'd be worried about cpu load)? If it does, is there a way to pre-compress the JS files so apache2 wouldn't have to do this for each file?

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  • Static DHCP!?

    - by voyager
    I've found some home wireless routers/ADSL+ modems (ZyXEL 660) talking about Static DHCP, when refering to assosiating a specific MAC to an IP, but still serve the configuration over DHCP. Doesn't this have another name? What does Cisco call this feature (that I know supports because I've used long time ago)?

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  • Assigning static IP to VPN server

    - by Akroy
    I have a Win2008 R2 server that is going to be receiving many VPN connections. I want to be able to staticly set the IP addresses of both ends of each connection based on the user. I easily found how to do this for the client: when you're managing the user account, go to "Dial-In" and click "Assign Static IP Addresses." Now, whenever a certain account dials in, I have control over their client VIP, but how do I set my server VIP for each account?

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  • How to get a static ip address on adsl

    - by user23950
    I tried it before by setting the ip address manually. And I used this IP Address: 192.168.1.33 I reboot and tried if I can connect to the internet, but no luck. It must be set to obtain your ip address automatically. Is there any way on getting a static ip address on an adsl/dsl

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  • Fix static ip address problems in Ubuntu 10.04

    - by jane
    I used Network Manager in Ubuntu 10.04 to set a static ip address and assigned one that was already in use. Now my computer will not boot (nfs crashes). I booted from a live cd to change the configuration on the file system in /etc/network/interfaces but the file looks to be the default. Where does the network manager (the gui from system- preferences) store it's configuration so I can overwrite it and enter the correct ip addresss and have a happy working computer again. thanks!!

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  • (static initialization order?!) problems with factory pattern

    - by smerlin
    Why does following code raise an exception (in createObjects call to map::at) alternativly the code (and its output) can be viewed here intererestingly the code works as expected if the commented lines are uncommented with both microsoft and gcc compiler (see here), this even works with initMap as ordinary static variable instead of static getter. The only reason for this i can think of is that the order of initialization of the static registerHelper_ object (factory_helper_)and the std::map object (initMap) are wrong, however i cant see how that could happen, because the map object is constructed on first usage and thats in factory_helper_ constructor, so everything should be alright shouldnt it ? I am even more suprised that those doNothing() lines fix the issue, because that call to doNothing() would happen after the critical section (which currently fails) is passed anyway. EDIT: debugging showed, that without the call to factory_helper_.doNothing(), the constructor of factory_helper_ is never called. #include <iostream> #include <string> #include <map> #define FACTORY_CLASS(classtype) \ extern const char classtype##_name_[] = #classtype; \ class classtype : FactoryBase<classtype,classtype##_name_> namespace detail_ { class registerHelperBase { public: registerHelperBase(){} protected: static std::map<std::string, void * (*)(void)>& getInitMap() { static std::map<std::string, void * (*)(void)>* initMap = 0; if(!initMap) initMap= new std::map<std::string, void * (*)(void)>(); return *initMap; } }; template<class TParent, const char* ClassName> class registerHelper_ : registerHelperBase { static registerHelper_ help_; public: //void doNothing(){} registerHelper_(){ getInitMap()[std::string(ClassName)]=&TParent::factory_init_; } }; template<class TParent, const char* ClassName> registerHelper_<TParent,ClassName> registerHelper_<TParent,ClassName>::help_; } class Factory : detail_::registerHelperBase { private: Factory(); public: static void* createObject(const std::string& objclassname) { return getInitMap().at(objclassname)(); } }; template <class TClass, const char* ClassName> class FactoryBase { private: static detail_::registerHelper_<FactoryBase<TClass,ClassName>,ClassName> factory_helper_; static void* factory_init_(){ return new TClass();} public: friend class detail_::registerHelper_<FactoryBase<TClass,ClassName>,ClassName>; FactoryBase(){ //factory_helper_.doNothing(); } virtual ~FactoryBase(){}; }; template <class TClass, const char* ClassName> detail_::registerHelper_<FactoryBase<TClass,ClassName>,ClassName> FactoryBase<TClass,ClassName>::factory_helper_; FACTORY_CLASS(Test) { public: Test(){} }; int main(int argc, char** argv) { try { Test* test = (Test*) Factory::createObject("Test"); } catch(const std::exception& ex) { std::cerr << "caught std::exception: "<< ex.what() << std::endl; } #ifdef _MSC_VER system("pause"); #endif return 0; }

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  • non-static method cannot be referenced from a static context

    - by Mith
    I am modifying the source code here: http://thinkandroid.wordpress.com/2009/12/30/getting-response-body-of-httpresponse/ I get this error: non-static method getContentCharSet(org.apache.http.HttpEntity) cannot be referenced from a static context String charset = getContentCharSet(entity); This error is line 13 on the second box. Any ideas? I have been really struggling with this code :-(

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  • Can static methods be called using object/instance in .NET

    Ans is Yes and No   Yes in C++, Java and VB.NET No in C#   This is only compiler restriction in c#. You might see in some websites that we can break this restriction using reflection and delegates, but we can’t, according to my little research J I shall try to explain you…   Following is code sample to break this rule using reflection, it seems that it is possible to call a static method using an object, p1 using System; namespace T {     class Program     {         static void Main()         {             var p1 = new Person() { Name = "Smith" };             typeof(Person).GetMethod("TestStatMethod").Invoke(p1, new object[] { });                     }         class Person         {             public string Name { get; set; }             public static void TestStatMethod()             {                 Console.WriteLine("Hello");             }         }     } } but I do not think so this method is being called using p1 rather Type Name “Person”. I shall try to prove this… look at another example…  Test2 has been inherited from Test1. Let’s see various scenarios… Scenario1 using System; namespace T {     class Program     {         static void Main()         {             Test1 t = new Test1();            typeof(Test2).GetMethod("Method1").Invoke(t,                                  new object[] { });         }     }     class Test1     {         public static void Method1()         {             Console.WriteLine("At test1::Method1");         }     }       class Test2 : Test1     {         public static void Method1()         {             Console.WriteLine("At test1::Method2");         }     } } Output:   At test1::Method2 Scenario2         static void Main()         {             Test2 t = new Test2();            typeof(Test2).GetMethod("Method1").Invoke(t,                                          new object[] { });         }   Output:   At test1::Method2   Scenario3         static void Main()         {             Test1 t = new Test2();            typeof(Test2).GetMethod("Method1").Invoke(t,                             new object[] { });         }   Output: At test1::Method2 In all above scenarios output is same, that means, Reflection also not considering the object what you pass to Invoke method in case of static methods. It is always considering the type which you specify in typeof(). So, what is the use passing instance to “Invoke”. Let see below sample using System; namespace T {     class Program     {         static void Main()         {            typeof(Test2).GetMethod("Method1").                Invoke(null, new object[] { });         }     }       class Test1     {         public static void Method1()         {             Console.WriteLine("At test1::Method1");         }     }     class Test2 : Test1     {         public static void Method1()         {             Console.WriteLine("At test1::Method2");         }     } }   Output is   At test1::Method2   I was able to call Invoke “Method1” of Test2 without any object.  Yes, there no wonder here as Method1 is static. So we may conclude that static methods cannot be called using instances (only in c#) Why Microsoft has restricted it in C#? Ans: Really there Is no use calling static methods using objects because static methods are stateless. but still Java and C++ latest compilers allow calling static methods using instances. Java sample class Test {      public static void main(String str[])      {            Person p = new Person();            System.out.println(p.GetCount());      } }   class Person {   public static int GetCount()   {      return 100;   } }   Output          100 span.fullpost {display:none;}

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  • Static file download from browser breaking in varnish but works fine in Apache

    - by Ron
    I would at first like to thank everyone at serverfault for this great website and I also come to this site while searching in google for various server related issues and setups. I also have an issue today and so I am posting here and hope that the seniors would help me out. I had setup a website on a dedicated server a few days ago and I used Varnish 3 as the frontend to Apache2 on a Debian Lenny server as the traffic was a bit high. There are several static file downloads of around 10-20 MB in size in the website. The website looked fine in the last few days after I setup. I was checking from a 5mbps + broadband connection and the file downloads were also completed in seconds and working fine. But today I realized that on a slow internet connection the file downloads were breaking off. When I tried to download the files from the website using a browser then it broke off after a minute or so. It kept on happening again and again and so it had nothing to do with the internet connection. The internet connection was around 512 kbps and so it was not dial up level speed too but decent speed where files should easily download though not that fast. Then I thought of trying out with the apache backend port and used the port number to check out if the problem occurs. But then on adding the apache port in the static file download url, the files got downloaded easily and did not break even once. I tried it several times to make sure that it was not a coincidence but every time I was using the apache port in the file download url then it was downloading fine while it was breaking each time with the normal link which was routed through Varnish I suppose. So, it seems Varnish has somehow resulted in the broken file downloads. Could anyone give any idea as to why it is happening and how to fix the problem. For more clarification, take this example: Apache backend set on port 8008, Varnish frontend set on port 80 Now when I download say http://mywebsite.com/directory/filename.extension Then the download breaks off after a minute or so. I cannot be sure it is due to the time or size though and I am just assuming. May be some other reason too. But when I download using: http://mywebsite.com:8008/directory/filename.extension Then the file download does not break at all and it gets download fine. So, it seems that varnish is somehow creating the file download breaking and not apache. Does anybody have any idea as to why it is happening and how can it be fixed. Any help would be highly appreciated. And my varnish default.vcl is backend apache { set backend.host = "127.0.0.1"; set backend.port = "8008"; } sub vcl_deliver { remove resp.http.X-Varnish; remove resp.http.Via; remove resp.http.Age; remove resp.http.Server; remove resp.http.X-Powered-By; }

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  • How does GCC compile applications that reference a static library

    - by technobrat
    I've read that the gcc compiler can perform certain optimization when compiling an application that references a static library, for instance - it will "pull" in only that code from the static library that the application depends upon. This helps keep the size of the application's executable to a minimum if portions of the static library are not being used by the app. 1) Is this true? 2) How does GCC know what code from the static library the application is actually using? Does it only look t the header files that are included (directly and indirectly) in the application and then pull code accordingly? Or does it actually look at what methods from the static library are being called?

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