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  • problem understanding templates in c++

    - by hidayat
    Template code is not compiled until the template function is used. But where does it save the compiled code, is it saved in the object file from which used the template function in the first place? For example, main.cpp is calling a template function from the file test.h, the compiler generates an object file main.o, Is the template function inside the main.o file? because template code is not inlined, is it?

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  • Understanding the singleton class when aliasing a instance method

    - by Backo
    I am using Ruby 1.9.2 and the Ruby on Rails v3.2.2 gem. I am trying to learn Metaprogramming "the right way" and at this time I am aliasing an instance method in the included do ... end block provided by the RoR ActiveSupport::Concern module: module MyModule extend ActiveSupport::Concern included do # Builds the instance method name. my_method_name = build_method_name.to_sym # => :my_method # Defines the :my_method instance method in the including class of MyModule. define_singleton_method(my_method_name) do |*args| # ... end # Aliases the :my_method instance method in the including class of MyModule. singleton_class = class << self; self end singleton_class.send(:alias_method, :my_new_method, my_method_name) end end "Newbiely" speaking, with a search on the Web I came up with the singleton_class = class << self; self end statement and I used that (instead of the class << self ... end block) in order to scope the my_method_name variable, making the aliasing generated dynamically. I would like to understand exactly why and how the singleton_class works in the above code and if there is a better way (maybe, a more maintainable and performant one) to implement the same (aliasing, defining the singleton method and so on), but "the right way" since I think it isn't so.

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  • Java - understanding servlets

    - by Trup
    I am working on a homework project that should implement a board game between 2 clients over an HttpServlet. I have couple of questions: 1) I read that HttpServlets must be stateless, however, for the sake of the game, I have to keep a lot of state(whose turn it is, the state of the board, etc). Do I have to keep this in the clients? Does the HttpServlet indeed have to be stateless, i.e. have no fields that track state? 2) I know that the clients will talk to the servlet via the doGet/doPost methods, but how can the servlet talk to the clients(for example, if player 1 just made a move and sent it to the servlet, the servlet has to tell client 2 what the move was). Thank you Also, if you can point me to a useful, simple example of a similar code online, I would be very grateful

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  • understanding syb boilerplate elimination

    - by Pradeep
    In the example given in http://web.archive.org/web/20080622204226/http://www.cs.vu.nl/boilerplate/ -- Increase salary by percentage increase :: Float -> Company -> Company increase k = everywhere (mkT (incS k)) -- "interesting" code for increase incS :: Float -> Salary -> Salary incS k (S s) = S (s * (1+k)) how come increase function compiles without binding anything for the first Company mentioned in its type signature. Is it something like assigning to a partial function? Why is it done like that?

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  • understanding a Build c++

    - by numerical25
    I think I know what a build is. But I am not sure. My definition of a build is another word for saying compiled application. Can someone please tell me what exactly a build is. And why do people ask for 2 types of builds. Such as Debug Build, Profile Build and a Release Build. What are the differences.

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  • Understanding Incrementing

    - by Chad
    For example this: var a = 123; var b = a++; now a contains 124 and b contains 123 I understand that b is taking the value of a and then a is being incremented. However, I don't understand why this is so. The principal reason for why the creators of JavaScript would want this. Is this really more useful than doing it the PHP way? What is the advantage to this other than confusing newbies?

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  • Not Understanding Basics Of Dynamic DataBinding (bindPropety) In Flex

    - by Joshua
    I need to dynamically bind properties of components created at runtime. In this particular case please assume I need to use bindProperty. I don't quite understand why the following simplistic test is failing (see code). When I click the button, the label text does not change. I realize that there are simpler ways to go about this particular example using traditional non-dynamic binding, but I need to understand it in terms of using bindProperty. Can someone please help me understand what I'm missing? <?xml version="1.0" encoding="utf-8"?> <mx:WindowedApplication xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" xmlns:ns1="Tools.*" minWidth="684" minHeight="484" xmlns:ns2="*" creationComplete="Init();"> <mx:Script> <![CDATA[ import mx.collections.ArrayCollection; import mx.binding.utils.*; public var Available:ArrayCollection=new ArrayCollection(); public function get Value():String { return (Available.getItemAt(0).toString()); } public function Init():void { Available.addItemAt('Before', 0); BindingUtils.bindProperty(Lab, 'text', this, 'Value'); } public function Test():void { Available.setItemAt('After', 0); } ]]> </mx:Script> <mx:Label x="142" y="51" id="Lab"/> <mx:Button x="142" y="157" label="Button" click="Test();"/> </mx:WindowedApplication> Thanks in advance.

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  • Understanding a #define directive

    - by Meta
    Looking at the Windows SDK, I found this #define directive for MAKEINTRESOURCEW: #define MAKEINTRESOURCEW(i) ((LPWSTR)((ULONG_PTR)((WORD)(i)))) Can someone explain to me what the heck that means? For example, what would be the value of MAKEINTRESOURCEW(0)? (1)? (-1)?

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  • Understanding Security Certificates (and thier pricing)

    - by John Robertson
    I work at a very small company so certificate costs need to be absolutely minimal. However for some applications we do Need to have our customers get that warm fuzzy not-using-a-self-signed certificate feeling. Since creating a "certificate authority" with makecert really just means creating a public/private key pair, it seems pretty clear that creating a public/private key pair FROM such a "certificate authority" really just means generating a second public/private key pair and signing both with the private key that belongs to the "certificate authority". Since the keys are signed anyone can verify they came from the certificate authority I created, or if verisign gave me the pair they sign it with one of their own private keys, and anyone can use verisigns corresponding public key to confirm verisign as the source of the keys. Given this I don't understand when I go to verisign or godaddy why they have rates only for yearly plans, when all I really want from them is a single public/private key pair signed with one of their private keys (so that anyone else can use their public keys to confirm that, yes, they gave me that public/private key pair and they confirmed I was who I said I was so you can trust my public/private key pair as belonging to a legitimate third party). Clearly I am misunderstanding something, what is it? Does verisign retire their public/private key pairs periodically so that my verisign signed key pair "expires" and I need new ones?

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  • Help understanding this stack trace

    - by user80632
    Hi I have health monitoring turned on, and i have the following error i'm trying to understand: Exception: Exception information: Exception type: System.InvalidCastException Exception message: Specified cast is not valid. Thread information: Thread ID: 5 Thread account name: NT AUTHORITY\NETWORK SERVICE Is impersonating: False Stack trace: at _Default.Repeater1_ItemDataBound(Object sender, RepeaterItemEventArgs e) at System.Web.UI.WebControls.Repeater.CreateControlHierarchy(Boolean useDataSource) at System.Web.UI.WebControls.Repeater.OnDataBinding(EventArgs e) at _Default.up1_Load() at _Default.Timer1_Tick(Object sender, EventArgs e) at System.Web.UI.Timer.OnTick(EventArgs e) at System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) I'm just trying to figure out exactly where the problem is happening and what it is - is it happening in the Repeater1_ItemDataBound sub routine, or in the Timer1_Tick sub routine? Is the last thing that happened before the error occured at the top or bottom of the trace? any help much appreciated thanks

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  • Understanding prolog [lists]

    - by wwrob
    I am to write a program that does this: ?- pLeap(2,5,X,Y). X = 2, Y = 3 ; X = 3, Y = 4 ; X = 4, Y = 5 ; X = 5, Y = 5 ; false. (gives all pairs X,X+1 between 2 and 5, plus the special case at the end). This is supposedly the solution. I don't really understand how it works, could anyone guide me through it? pLeap(X,X,X,X). pLeap(L,H,X,Y) :- L<H, X is L, Y is X+1. pLeap(L,H,X,Y) :- L=<H, L1 is L+1, pLeap(L1,H,X,Y). I'd do it simply like this: pLeap(L,H,X,Y) :- X >= L, X =< H, Y is X+1. Why doesn't it work (ignoring the special case at the end)?

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  • Understanding reflection

    - by sdmiller
    I recently started work at a new company and a .net web application we have is built using reflection. I have only been out of school for a year and haven't worked with this concept. After studying the code... it looks like there is a single backend interface of type object that has about 20 classes that inherit from it. lots of generic gets and sets On the surface it looks like standard inheritance to me. I guess my question is, what makes this reflection? Is it because the interface is not strongly typed? Thanks

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  • Better understanding of my SQL transactions

    - by Slew Poke
    I just realized that my application was needlessly making 50+ database calls per user request due to some hidden coding -- hidden in the sense that between LINQ, persistence frameworks and events it just so turned out that a huge number of calls were being made without me being aware. Is there a recommended way to analyze individual transactions going to my SQL 2008 database, preferably with some integration to my Visual Studio 2010 environment? I want to be able to 'spy' on individual transactions being made, but only for certain pieces of my code, and without making serious changes to either the code or database.

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  • Understanding "this" keyword

    - by Raffaele
    In this commit there is a change I cannot explain deferred.done.apply( deferred, arguments ).fail.apply( deferred, arguments ); becomes deferred.done( arguments ).fail( arguments ); AFAIK, when you invoke a function as a member of some object like obj.func(), inside the function this is bound to obj, so there would be no use invoking a function through apply() just to bound this to obj. Instead, according to the comments, this was required because of some preceding $.Callbacks.add implementation. My doubt is not about jQuery, but about the Javascript language itself: when you invoke a function like obj.func(), how can it be that inside func() the this keyword is not bound to obj?

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  • Understanding omission failure in distributed systems

    - by karthik A
    The following text says this which I'm not able to quite agree : client C sends a request R to server S. The time taken by a communication link to transport R over the link is D. P is the maximum time needed by S to recieve , process and reply to R. If omission failure is assumed ; then if no reply to R is received within 2(D+P) , then C will never recieve a reply to R . Why is the time here 2(D+P). As I understand shouldn't it be 2D+P ?

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  • Java Inheritance Concept Understanding

    - by Nirmal
    Hello All.... I am just refreshing the oops features of the java. So, I have a little confusion regarding inheritance concept. For that I have a following sample code : class Super{ int index = 5; public void printVal(){ System.out.println("Super"); } } class Sub extends Super{ int index = 2; public void printVal(){ System.out.println("Sub"); } } public class Runner { public static void main(String args[]){ Super sup = new Sub(); System.out.println(sup.index+","); sup.printVal(); } } Now above code is giving me output as : 5,Sub. Here, we are overriding printVal() method, so that is understandable that it is accessing child class method only. But I could not understand why it's accessing the value of x from Super class... Thanks in advance....

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  • Understanding java's native threads and the jvm

    - by Moev4
    I understand that the jvm is itself an application that turns the bytecode of the java executable into native machine code, but when using native threads I have some questions that I just cannot seem to answer. Does every thread create their own instance of the jvm to handle their particular execution? If not then does the jvm have to have some way to schedule which thread it will handle next, if so wouldn't this render the multi-threaded nature of java useless since only one thread can be ran at a time?

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  • understanding the ORM models in MVC

    - by fayer
    i cant fully understand the ORM models in MVC. so i am using symfony with doctrine. the doctrine models are created. does this mean that i don't have to create any models? are the doctrine models the only models i need? where should i put the code that uses the doctrine models: eg. $phoneIds = array(); $phone1 = new Phonenumber(); $phone1['phonenumber'] = '555 202 7890'; $phone1->save(); $phoneIds[] = $phone1['id']; $phone2 = new Phonenumber(); $phone2['phonenumber'] = '555 100 7890'; $phone2->save(); $phoneIds[] = $phone2['id']; $user = new User(); $user['username'] = 'jwage'; $user['password'] = 'changeme'; $user->save(); $user->link('Phonenumbers', $phoneIds); should this code be in the controller or in another model? and where should i validate these fields (check if it exists in database, that email is email etc)? could someone please shed a light on this. thanks.

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  • Need some help understanding a weird C behavior

    - by mike
    This part of my code works fine: #include <stdio.h> int main(){ //char somestring[3] = "abc"; int i, j; int count = 5; for((i=0) && (j=0); count > 0; i++ && j++){ printf("i = %d and j = %d\n", i, j); count--; } return 0; } The output as expected: i : 0 and j : 0 i : 1 and j : 1 i : 2 and j : 2 i : 3 and j : 3 i : 4 and j : 4 Things get weird when I uncomment the char string declaration on the first line of the function body. #include <stdio.h> int main(){ char somestring[3] = "abc"; ... } The output: i : 0 and j : 4195392 i : 1 and j : 4195393 i : 2 and j : 4195394 i : 3 and j : 4195395 i : 4 and j : 4195396 What's the logic behind this? I'm using gcc 4.4.1 on Ubuntu 9.10.

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  • Problem in understanding connectSlotsByName() in pyqt???

    - by Jebagnanadas
    Hi all, I couldn't understand the connectSlotsByName() method which is predominently used by pyuic4.. As far the class is single in a PyQt file it's ok since we can use self which will be associated with a single object throughout.. But when we try to use various classes from different files the problem and the need to use connectSlotsByName() arises.. Here's what i encountered which is weird.. I created a stacked widget.. I placed my first widget on it.. It has a button called "Next ". On clicking next it hides the current widget and adds another widget which has the "click me" button.. The problem here is the click event for "click me" button in second is not captured.. It's a minimal example that i can give for my original problem.. Please help me.. This is file No.1..(which has the parent stacked widget and it's first page). On clicking next it adds the second page which has "clickme" button in file2.. from PyQt4 import QtCore, QtGui import file2 class Ui_StackedWidget(QtGui.QStackedWidget): def __init__(self,parent=None): QtGui.QStackedWidget.__init__(self,parent) self.setObjectName("self") self.resize(484, 370) self.setWindowTitle(QtGui.QApplication.translate("self", "stacked widget", None, QtGui.QApplication.UnicodeUTF8)) self.createWidget1() def createWidget1(self): self.page=QtGui.QWidget() self.page.setObjectName("widget1") self.pushButton=QtGui.QPushButton(self.page) self.pushButton.setGeometry(QtCore.QRect(150, 230, 91, 31)) self.pushButton.setText(QtGui.QApplication.translate("self", "Next >", None, QtGui.QApplication.UnicodeUTF8)) self.addWidget(self.page) QtCore.QMetaObject.connectSlotsByName(self.page) QtCore.QObject.connect(self.pushButton,QtCore.SIGNAL('clicked()'),self.showWidget2) def showWidget2(self): self.page.hide() obj=file2.widget2() obj.createWidget2(self) if __name__ == "__main__": import sys app = QtGui.QApplication(sys.argv) ui = Ui_StackedWidget() ui.show() sys.exit(app.exec_()) Here's file2 from PyQt4 import QtGui,QtCore class widget2(): def createWidget2(self,parent): self.page = QtGui.QWidget() self.page.setObjectName("page") self.parent=parent self.groupBox = QtGui.QGroupBox(self.page) self.groupBox.setGeometry(QtCore.QRect(30, 20, 421, 311)) self.groupBox.setObjectName("groupBox") self.groupBox.setTitle(QtGui.QApplication.translate("self", "TestGroupBox", None, QtGui.QApplication.UnicodeUTF8)) self.pushButton = QtGui.QPushButton(self.groupBox) self.pushButton.setGeometry(QtCore.QRect(150, 120, 92, 28)) self.pushButton.setObjectName("pushButton") self.pushButton.setText(QtGui.QApplication.translate("self", "Click Me", None, QtGui.QApplication.UnicodeUTF8)) self.parent.addWidget(self.page) self.parent.setCurrentWidget(self.page) QtCore.QMetaObject.connectSlotsByName(self.page) QtCore.QObject.connect(self.pushButton,QtCore.SIGNAL('clicked()'),self.printMessage) def printMessage(self): print("Hai") Though in both the widgets(i mean pages) QtCore.QMetaObject.connectSlotsByName(self.page) the clicked signal in second dialog isn't getting processed. Thanks in advance.. Might be a beginner question..

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  • Understanding Scope on Scala's For Loops (For Comprehension)

    - by T. Stone
    In Chapter 3 of Programming Scala, the author gives two examples of for loops / for comprehensions, but switches between using ()'s and {}'s. Why is this the case, as these inherently look like they're doing the same thing? Is there a reason breed <- dogBreeds is on the 2nd line in example #2? // #1 ()'s for (breed <- dogBreeds if breed.contains("Terrier"); if !breed.startsWith("Yorkshire") ) println(breed) // #2 {}'s for { breed <- dogBreeds upcasedBreed = breed.toUpperCase() } println(upcasedBreed)

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  • Problem understanding Inheritance

    - by dhruvbird
    I've been racking my brains over inheritance for a while now, but am still not completely able to get around it. For example, the other day I was thinking about relating an Infallible Human and a Fallible Human. Let's first define the two: Infallible Human: A human that can never make a mistake. It's do_task() method will never throw an exception Fallible Human: A human that will occasionally make a mistakes. It's do_task() method may occasionally throw a ErrorProcessingRequest Exception The question was: IS an infallible human A fallible human OR IS a fallible human AN infallible human? The very nice answer I received was in the form of a question (I love these since it gives me rules to answer future questions I may have). "Can you pass an infallible human where a fallible human is expected OR can you pass a fallible human where an infallible human is expected?" It seems apparent that you can pass an infallible human where a fallible human is expected, but not the other way around. I guess that answered my question. However, it still feels funny saying "An infallible human is a fallible human". Does anyone else feel queasy when they say it? It almost feels as if speaking out inheritance trees is like reading out statements from propositional calculus in plain English (the if/then implication connectives don't mean the same as that in spoken English). Does anyone else feel the same?

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  • Lack of understanding crash report

    - by Alan Lai
    I have this crash report. Incident Identifier: CA9E350A-C842-4349-AAD8-E9E62E93BDD1 CrashReporter Key: 360bc129d2f79a48e291eb5ca38b24e822ed5b6b Hardware Model: xxx Process: OrientalDailyiOS [1502] Path: /var/mobile/Applications/39480A57-68FF-4C46-8445-340EFE204119/OrientalDailyiOS.app/OrientalDailyiOS Identifier: OrientalDailyiOS Version: ??? (???) Code Type: ARM (Native) Parent Process: launchd [1] Date/Time: 2012-10-14 15:49:10.884 -0700 OS Version: iOS 6.0 (10A403) Report Version: 104 Exception Type: EXC_CRASH (SIGABRT) Exception Codes: 0x0000000000000000, 0x0000000000000000 Crashed Thread: 0 Last Exception Backtrace: 0 CoreFoundation 0x37a0a29e __exceptionPreprocess + 158 1 libobjc.A.dylib 0x34e3197a objc_exception_throw + 26 2 CoreFoundation 0x37955b70 -[__NSArrayM objectAtIndex:] + 160 3 OrientalDailyiOS 0x00064fdc -[Main_NewsDetail viewDidLoad] (Main_NewsDetail.m:43) 4 UIKit 0x386cb590 -[UIViewController loadViewIfRequired] + 360 5 UIKit 0x38757336 -[UIViewController shouldAutorotate] + 22 6 UIKit 0x38798cd4 -[UIWindowController transition:fromViewController:toViewController:target:didEndSelector:] + 1540 7 UIKit 0x38797fca -[UIViewController presentViewController:withTransition:completion:] + 3390 8 UIKit 0x388ba252 -[UIViewController presentModalViewController:animated:] + 26 9 Foundation 0x34364a6a __NSFireDelayedPerform + 446 10 CoreFoundation 0x379df5da __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 10 11 CoreFoundation 0x379df28c __CFRunLoopDoTimer + 268 12 CoreFoundation 0x379ddefc __CFRunLoopRun + 1228 13 CoreFoundation 0x37950eb8 0x37948000 + 36536 14 CoreFoundation 0x37950d44 CFRunLoopRunInMode + 100 15 GraphicsServices 0x373e32e6 GSEventRunModal + 70 16 UIKit 0x387002fc 0x386a9000 + 357116 17 OrientalDailyiOS 0x0005fac2 main (main.m:16) 18 OrientalDailyiOS 0x0005fa84 0x5e000 + 6788 However, I couldn't know where is error, I play around with my apps but show no error. I also tried iOS 6 with iPad, no problem. what apple feedback was We found that your app crashed on iPad running iOS 6, which is not in compliance with the App Store Review Guidelines. Your app crashed on both Wi-Fi and cellular networks when we: 1. Launch the app. 2. Tap any item on main page. 3. App crashes.

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