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• What all does a compiler add to an empty class declaration?

  - by cambr

  Suppose, I write class A { }; compiler should provide (as and when needed) a constructor a destructor a copy constructor = operator Is this all what the compiler provides? Are there any additions or deletions to this list?

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• Any way to access the type of a Scala Option declaration at runtime using reflection?

  - by Graham Lea

  So, I have a Scala class that looks like this: class TestClass { var value: Option[Int] = None } and I'm tackling a problem where I have a String value and I want to coerce it into that Option[Int] at runtime using reflection. To do so, I need to know that the field is an Option and that the type parameter of the Option is Int. What are my options for figuring out that the type of 'value' is Option[Int] at runtime (i.e. using reflection)? I have seen similar problems solved by annotating the field, e.g. @OptionType(Int.class). I'd prefer a solution that didn't require annotations on the reflection target if possible.

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• Why do I have to specify virtual functions in the declaration of a derived class?

  - by neuviemeporte

  Given the base class A and the derived class B: class A { public: virtual void f(); } class B : public A { public: void g(); } I get errors saying that f() is not declared in B while trying do define void B::f(). Do I have to declare f() explicitly in B? I think that if the interface changes I shouldn't have to correct the declarations in every single class deriving from it. Is there no way for B to get all the virtual functions' declarations from A automatically?

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• Understanding connection tracking in iptables

  - by Matt

  I'm after some clarification of the state/connection tracking in iptables. What is the difference between these rules? iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT iptables -A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT Is connection tracking turned on when a packet is first matched containing -m state --state BLA , or is connection tracking always on? Can/Should connection state be used for fast matching like below? e.g. suppose this is some sort of router/firewall (no nat). # Default DROP policy iptables -P INPUT DROP iptables -P OUTPUT DROP iptables -P FORWARD DROP # Drop invalid iptables -A FORWARD -m state --state INVALID -j DROP # Accept established,related connections iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT # Allow ssh through, track connection iptables -A FORWARD -p tcp --syn --dport 22 -m state --state NEW -j ACCEPT

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• Is there a downside to adding an anonymous empty delegate on event declaration?

  - by serg10

  I have seen a few mentions of this idiom (including on SO): // Deliberately empty subscriber public event EventHandler AskQuestion = delegate {}; The upside is clear - it avoids the need to check for null before raising the event. However, I am keen to understand if there are any downsides. For example, is it something that is in widespread use and is transparent enough that it won't cause a maintenance headache? Is there any appreciable performance hit of the empty event subscriber call?

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• In a C function declaration, what does "..." as the last parameter do?

  - by alaamh

  Often I see a function declared like this: void Feeder(char *buff, ...) what does "..." mean?

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• emacs: is there a semantic-jump-to-declaration (using semantic.el)?

  - by Cheeso

  Suppose I am editing a buffer containing C code. I have started semantic with semantic-load-enable-code-helpers . I have point placed on the name of a function . If I then invoke senator-jump I can jump to the place where that fn is first declared, in that module. What if it is an extern? Is it possible to use senator to jump to the definition of the fn, which resides in a separate module? Thanks.

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• Why size_t arguments in template declaration need to be const?

  - by ArunSaha

  I can have std::bitset< 10 > bitsetA; or const size_t LengthB = 20; std::bitset< LengthB > bitsetB; without any problem. But, if the length is not const size_t LengthC = 30; std::bitset< LengthC > bitsetC; // Line 30, say I face the following compilation error 'LengthC' cannot appear in a constant-expression template argument 1 is invalid What is the reason for that? What would be the problem, for compiler and for user code, if line 30 was to be accepted? Is it because LengthC might have some alias?

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• Why do I have to specify pure virtual functions in the declaration of a derived class in Visual C++?

  - by neuviemeporte

  Given the base class A and the derived class B: class A { public: virtual void f() = 0; }; class B : public A { public: void g(); }; void B::g() { cout << "Yay!"; } void B::f() { cout << "Argh!"; } I get errors saying that f() is not declared in B while trying do define void B::f(). Do I have to declare f() explicitly in B? I think that if the interface changes I shouldn't have to correct the declarations in every single class deriving from it. Is there no way for B to get all the virtual functions' declarations from A automatically? EDIT: I found an article that says the inheritance of pure virtual functions is dependent on the compiler: http://www.objectmentor.com/resources/articles/abcpvf.pdf I'm using VC++2008, wonder if there's an option for this.

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• What is the effect of final variable declaration in methods?

  - by Finbarr

  Classic example of a simple server: class ThreadPerTaskSocketServer { public static void main(String[] args) throws IOException { ServerSocket socket = new ServerSocket(80); while (true) { final Socket connection = socket.accept(); Runnable task = new Runnable() { public void run() { handleRequest(connection); } }; new Thread(task).start(); } } } Why should the Socket be declared as final? Is it because the new Thread that handles the request could refer back to the socket variable in the method and cause some sort of ConcurrentModificationException?

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• Is there a better way to write this repetitive event-declaration code in C# when implementing an int

  - by Damien Wildfire

  I have a lot of code like the following, where I explicitly implement some events required by an interface. public class IMicrowaveNotifier { event EventHandler<EventArgs> DoorClosed; event EventHandler<EventArgs> LightbulbOn; // ... } public class Microwave : IMicrowaveNotifier { private EventHandler<EventArgs> _doorClosed; event EventHandler<EventArgs> IMicrowaveNotifier.DoorClosed { add { lock (this) _doorClosed += value; } remove { lock (this) _doorClosed -= value; } } private EventHandler<EventArgs> _lightbulbOn; event EventHandler<EventArgs> IMicrowaveNotifier.LightbulbOn { add { lock (this) _lightbulbOn += value; } remove { lock (this) _lightbulbOn -= value; } } // ... } You can see that much of this is boilerplate. In Ruby I'd be able to do something like this: class Microwave has_events :door_closed, :lightbulb_on, ... end Is there a similar shorter way of removing this boilerplate in C#? Update: I left a very important part out of my example: namely, the events getting implemented are part of an interface, and I want to implement it explicitly. Sorry for not mentioning this earlier!

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• What is the difference between a definition and a declaration?

  - by Maciek

  As title says, the meaning of both eludes me.

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• Difference in declaring IDisposable member in using block or at using block declaration?

  - by dotnetdev

  Hi, I have the code below: using (SqlCommand command = new SqlCommand()) { command.CommandType = System.Data.CommandType.StoredProcedure; command.Connection = new SqlConnection(); command.CommandText = ""; command.Parameters.Add(new SqlParameter("@ExperienceLevel", 3).Direction = System.Data.ParameterDirection.Input); SqlDataReader dataReader = command.ExecuteReader(); } Is there any functional impact in declaring the SqlConnection where I currently am declaring it as opposed to like so?: using (SqlCommand command = new SqlCommand()) using (SqlConnection connection = new SqlConnection()) Thanks

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• Why won't gcc compile a class declaration as a reference argument?

  - by Jorge

  This compiles fine in Visual studio, but why not in XCode? class A() {}; someMethod(A& a); someMethod(A()); //error: no matching function call in XCode only :( Is this bad form? it seems annoying to have to write the following every time: A a(); someMethod(a); //successful compile on Xcode Am i missing something? I am not very experienced so thank you for any help!

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• Not Possible to Reference self in a Method Declaration?

  - by phasetwenty

  I wanted to write a method with an argument that defaults to a member variable like so: def method(self, arg1=0, arg2=self.member): Apparently this is not allowed. Should I write it a different way, or perhaps use a value of arg2 to signal when to use a different value?

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• What are the things that optimize speed declaration do in CL?

  - by kunjaan

  What are some of the optimization steps that this command does `(optimize speed (safety 0))` Can I handcode some of these techniques in my Lisp/Scheme program?

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• Scheme - What is wrong with my attempt to extend this declaration?

  - by CppLearner

  This is a homework question. Question My attempt (the whole file): http://pastebin.com/vt3Q3dqs If you search let var = exp1 in body, that's the function I need to extend according to the question. When I test the sample code above, I get an error apply-env: No binding for y (eval "let x = 30 in let x = -(x,1) y = -(x,2) in -(x,y)") ; The following is execution log The-next-two-lines-shows-var-and-exp1 (x) (#(struct:const-exp 30)) diff-exp #(struct:var-exp x) #(struct:const-exp 1) diff-exp #(struct:var-exp x) #(struct:const-exp 2) The-next-two-lines-shows-var-and-exp1 (x y) (#(struct:diff-exp #(struct:var-exp x) #(struct:const-exp 1)) #(struct:diff-exp #(struct:var-exp x) #(struct:const-exp 2))) diff-exp #(struct:var-exp x) #(struct:var-exp y) As you can see, when the interperter reads the last line -(x,y) it complains because there is no binding. What did I do wrong? I know this is really long language, but if anyone can kindly lead me to the right direction would be really really nice. Thank you!

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• What is the difference of declaration of a variable in a loop and before the loop?

  - by Ehsan Mamakani

  Look at this example: int i; for (i=1;i....... and this: for (int i=1;i........ What's the difference between them?

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• How to templatize the container type in a function declaration?

  - by Kyle

  I want to write a function that accepts any container holding strings. Something like this: template <typename Container> void foo(Container<string>& stuff); But this isn't the right syntax. What's the right syntax?

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• Port 21 will not open. status is closed. forward port 21 to new domains.

  - by Bob Swaggerty

  I am having a problem opening port 21 on my Linux Ubuntu server. No matter what i do, i can not get my status to change from closed to open. Here is a recent iptables command i used and the result iptables -A INPUT -p tcp -m tcp --dport 21 -j ACCEPT nmap -p21-22,25,80,443 CCR1 Starting Nmap 4.53 ( http://insecure.org ) at 2012-06-19 03:13 CDT Interesting ports on CCR1.chennaichristianradio.com (5.10.69.98): PORT STATE SERVICE 21/tcp closed ftp 22/tcp open ssh 25/tcp closed smtp 80/tcp open http 443/tcp closed https I also used commands from the advise from this forum http://www.cyberciti.biz/faq/iptables-open-ftp-port-21/ I need to open this for FTP access to the server, and ultimately I need to forward port 21 to 2 domains i am setting up. Thank you for any assistance you can provide -Bob Swaggerty

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• Make Gameobject Stand On Surface Facing Certain Direction

  - by Julian

  I want to make a biped character stand on any surface I click on. Surfaces have up vectors of any of positive or negative X,Y,Z. So imagine a cube with each face being a gameobject whose up vector pointing directly away from the cube. If my character is facing "forward" and I click on a surface which is to the left or right of me ( left or right walls), I want my character to now be standing on that surface but still be facing in the direction he initially was. If I click on a wall which is in the forward path of my character i want him to now be standing on that surface and his forward to now be what was once "up" relative to my character. Here is the code I am working with now. void Update() { if (Input.GetMouseButtonUp (0)) { RaycastHit hit; var ray = Camera.main.ScreenPointToRay(Input.mousePosition); if (Physics.Raycast(ray, out hit)) { Vector3 upVectBefore = transform.up; Vector3 forwardVectBefore = transform.forward; Quaternion rotationVectBefore = transform.rotation; Vector3 hitPosition = hit.transform.position; transform.position = hitPosition; float lookDifference = Vector3.Distance(hit.transform.up, forwardVectBefore); if(Vector3.Distance(hit.transform.up, upVectBefore) < .23) //Same normal { transform.rotation = rotationVectBefore; } else if(lookDifference > 1.412 && lookDifference <= 1.70607) //side wall { transform.up = hit.transform.up; transform.forward = forwardVectBefore; } else //head on wall { transform.up = hit.transform.up; transform.forward = upVectBefore; } } } } The first case "Same normal" works fine, however the other two do not work as I would like them to. Sometimes my character is laying down on the surface or on the wrong side of the surface. Does anyone know nice way of solving this problem?

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• fast forward/streaming in html5 video? RTSP?

  - by karpodiem

  right now I've got a few .mp4's hosted on Amazon S3. I know that S3 has support for RTMP, which is useful for streaming Flash. I'd like to accomplish something similar with html5 video; my biggest issue is that I need the ability to seek (fast forward) to a particular part of the video. Right now when I query the video, it loads the entire video before playing, which is a waste of bandwidth/dealbreaker. In what manner could this be implemented? Is this even possible? Looks like RTSP would be a good bet, but I haven't found whether anyone has rolled this out successfully.

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• How can I add forward class references used in the -Swift.h header?

  - by Bill

  I'm integrating Swift code into a large Objective-C project, but I'm running into problems when my Swift code refers to Objective-C classes. For example, suppose I have: An Objective-C class called MyTableViewController An Objective-C class called DeletionWorkflow I declared a Swift class as follows: class DeletionVC: MyTableViewController { let deleteWorkflow: DeletionWorkflow ... } If I now try to use this class by importing ProjectName-Swift.h into Objective-C code, I get undefined symbol errors for both MyTableViewController and DeletionWorkflow. I can fix the problem in that individual source file by importing DeletionWorkflow.h and MyTableViewController.h before I import ProjectName-Swift.h but this doesn't scale up to a large project where I want my Swift and Objective-C to interact often. Is there a way to add forward class references to ProjectName-Swift.h so that these errors don't occur when I try to use Swift classes from Objective-C code in my app?

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• How to wrtie a XML License Line(ended with a forward slash '/') in C#?

  - by Nano HE

  I want to write a XML file as below: <?xml version="1.0" encoding="UTF-8"?> <books xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"> <License licenseId="" licensePath="" /> Some piece of my code attached here // Create a new file in D:\\ and set the encoding to UTF-8 XmlTextWriter textWriter = new XmlTextWriter("D:\\books.xml", System.Text.Encoding.UTF8); // Format automatically textWriter.Formatting = Formatting.Indented; // Opens the document textWriter.WriteStartDocument(); // Write the namespace declaration. textWriter.WriteStartElement("books", null); // Write the genre attribute. textWriter.WriteAttributeString("xmlns", "xsd", null, "http://www.w3.org/2001/XMLSchema"); textWriter.WriteAttributeString("xmlns", "xsi", null, "http://www.w3.org/2001/XMLSchema-instance"); And now I need to write the License Line below in C# <License licenseId="" licensePath="" /> But I don't know how to move on for I found the Line ended with the forward slash / .Thank you.

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• How To use Simple Html Video Player Also Have Rewind Forward Capability For The Next Video ?? PHP HTML

  - by Syed Raza

  i am trying to use this code for video in html but fistle it is for flash videos and second thing is that it do not have rewind forward capability for the next video clip my code is, <object classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=8,0,0,0" width="250" height="250" align="middle"> <param name="allowScriptAccess" value="sameDomain"/> <param name="movie" value="Pro Tools Tutorials.swf"/> <param name="quality" value="high"/> <param name="bgcolor" value="#000000"/> <param name="allowFullScreen" value="true"/> <embed src="/unknittingmouse1.swf" quality="high" align="middle" bgcolor="#ffffff" width="250" height="230" allowFullScreen="true" allowScriptAccess="sameDomain" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"> </embed> </object> we have to also be carefull that that video code will run on internet explorer Hopes to listen from you soon, thanks in advance

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