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• Why does C++ linking use virtually no CPU?

  - by John

  On a native C++ project, linking right now can take a minute or two, yet during this time CPU drops from 100% during compilation to virtually zero. Does this mean linking is primarily a disk activity? If so, is this the main area an SSD would make big changes? But, why aren't all my OBJ files (or as many as possible) kept in RAM after compilation to avoid this? With 4Gb of RAM I should be able to save a lot of disk access and make it CPU-bound again, no?

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• Why should pop() take an argument?

  - by Stephano

  Quick background I'm a Java developer who's been playing around with C++ in my free/bored time. Preface In C++, you often see pop taking an argument by reference: void pop(Item& removed); I understand that it is nice to "fill in" the parameter with what you removed. That totally makes sense to me. This way, the person who asked to remove the top item can have a look at what was removed. However, if I were to do this in Java, I'd do something like this: Item pop() throws StackException; This way, after the pop we return either: NULL as a result, an Item, or an exception would be thrown. My C++ text book shows me the example above, but I see plenty of stack implimentations taking no arguments (stl stack for example). The Qustion How should one implement the pop function in C++? The Bonus Why?

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• Why is comparing against "end()" iterator legal?

  - by sharptooth

  According to C++ standard (3.7.3.2/4) using (not only dereferencing, but also copying, casting, whatever else) an invalid pointer is undefined behavior (in case of doubt also see this question). Now the typical code to traverse an STL containter looks like this: std::vector<int> toTraverse; //populate the vector for( std::vector<int>::iterator it = toTraverse.begin(); it != toTraverse.end(); ++it ) { //process( *it ); } std::vector::end() is an iterator onto the hypothetic element beyond the last element of the containter. There's no element there, therefore using a pointer through that iterator is undefined behavior. Now how does the != end() work then? I mean in order to do the comparison an iterator needs to be constructed wrapping an invalid address and then that invalid address will have to be used in a comparison which again is undefined behavior. Is such comparison legal and why?

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• Why is 'volatile' parasitic in C++?

  - by Steve

  Consider the following code: int main() { int i; volatile int* p = &i; int *v = p; return 0; } This gives an error in g++: $ g++ -o volatile volatile.cpp volatile.cpp: In function ‘int main()’: volatile.cpp:6: error: invalid conversion from ‘volatile int*’ to ‘int*’ My intention was that I want to make p volatile. However, once I've read the value of p, I don't care if accessing v is volatile. Why is it required that v be declared volatile? This is hypothetical code of course. In a real situation you could imagine that p points to a memory location, but is modified externally and I want v to point to the location that p pointed to at the time of v = p, even if later p is externally modified. Therefore p is volatile, but v is not. By the way I am interested in the behaviour both when this is considered C and C++, but in C this only generates a warning, not an error.

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• Why must use "out" instead of ref ?

  - by Phsika

  i wrote some code blocks about ref -out declaration. i think that ref is most useful out. Ok. why i need to use out. i can use always ref everytime: namespace out_ref { class Program { static void Main(string[] args) { sinifA sinif = new sinifA(); int test = 100; sinif.MethodA(out test); Console.WriteLine(test.ToString()); sinif.MethodB(ref test); Console.WriteLine(test.ToString()); Console.ReadKey(); } } class sinifA { public void MethodA(out int a) { a = 200; } int _b; public void MethodB(ref int b) { _b = b; b = 2*b; } } }

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• Why this java application print "true"?

  - by user292084

  This is my first Class Hello.java public class Hello { String name = ""; } This is my second Class Test1.java public class Test1 { public static void main(String[] args) { Hello h = new Hello(); Test1 t = new Test1(); t.build(h); System.out.println((h.name)); } void build(Hello h){ h.name = "me"; } } When I run Test1.java, it prints "me". I think I understand, because of "reference transfer". This is my third Class Test2.java public class Test2 { public static void main(String[] args) { Hello h = null; Test2 t = new Test2(); t.build(h); System.out.println(((h == null))); } void build(Hello h){ h = new Hello(); } } When I run Test2.java, it prints "true", why ? Is it "reference transfer" no longer? I am confused.

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• Why is it not saying I won?

  - by Itachi

  This is my if statement... The buttons show up like this: This is my if statement if((buttons[3].getName()=="x" && buttons[6].getName()=="x" && buttons[9].getText()=="x")||(buttons[2].getName()=="x" && buttons[5].getName()=="x" && buttons[8].getName()=="x")|| ((buttons[1].getName()=="x") && (buttons[4].getName()=="x") && (buttons[7].getName()=="x"))){ JOptionPane.showMessageDialog(null,"X Wins"); } So if I select the 1st, 4th and 7th buttons (the left most 3 buttons) why does it not say "X Wins"? As a sidenote, yes the buttons should have the name "x"

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• Why my WCF Service returns xml serialized objects?

  - by user294554

  Hi, I'm new here and I hope anyonte can help me. I have WCF Service and Windows Forms working with this client written in VB.NET. The Service class started to return xml serialized objects, but all my classes on Service side are DataContract-s and the service class is DataContractFormat. I googled everywhere about serializations and I couldn't find reason why it started to do that. I checked my classes and service, app.config file, but I couldn't find anything. I checked Reference.vb class, and it's System.Xml.Serialization.XmlElementAttribute everywhere. The question may seem dummy, but I really don't know what to do. I just want to know what can cause the service to act like that. Thank you.

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• Instance_eval: why the class of subclass is superclass

  - by Raj

  def singleton_class class << self self end end class Human proc = lambda { puts 'proc says my class is ' + self.name.to_s } singleton_class.instance_eval do define_method(:lab) do proc.call end end end class Developer < Human end Human.lab # class is Human Developer.lab # class is Human ; oops Following solution works. def singleton_class class << self self end end class Human proc = lambda { puts 'proc says my class is ' + self.name.to_s } singleton_class.instance_eval do define_method(:lab) do self.instance_eval &proc end end end class Developer < Human end Human.lab # class is Human Developer.lab # class is Human ; oops Why Developer.lab is reporting that it is Human ? And what can be done so that proc reports Developer when Developer.lab is invoked.

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• Why the compiler doesn't complain about this error ?

  - by M.H

  Hi I am writing some java questions to help my friends in the java exam. I wrote a question and I supposed that three errors will occurred in the code but the compiler complained only about two. the code is : class MyClass { static MyClass() { System.out.println("I am The First Statement here!"); this(); } } I expected the following errors : the constructor can't be static this can't be in a static function (since the constructor isn't valid) this here should be the first statement. NetBeans isn't complaining about the second error here. why ?

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• Why does Custom UITableViewCell *sometimes* cause an NSInvalidArgumentException?

  - by Wayne Hartman

  I have created a custom UITableViewCell, but when I dequeue the cell, sometimes it throws an NSInvalidArgumentException: [UITableViewCell nameLabel]: unrecognized selector sent to instance 0x3b4e7f0 Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '* -[UITableViewCell nameLabel]: unrecognized selector sent to instance 0x3b4e7f0' Now, my custom UITableViewCell does have an attribute nameLabel, so I am confused why it is throwing this error. Below is the code I use to dequeue the cell: - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { NSUInteger row = [indexPath row]; CTMenuItemVO* key = [[[self retrieveCartItems] allKeys] objectAtIndex:row]; NSNumber* quantity = [[self retrieveCartItems] objectForKey:key]; static NSString* SectionsTableIdentifier = @"SectionsTableIdentifier2"; OrderItemCell* cell = (OrderItemCell*)[tableView dequeueReusableCellWithIdentifier: SectionsTableIdentifier]; if (cell == nil) { NSArray* topLevelObjects = [[NSBundle mainBundle] loadNibNamed:@"OrderItemCell" owner:nil options:nil]; for(id currentObject in topLevelObjects) { if ([currentObject isKindOfClass:[UITableViewCell class]]) { cell = (OrderItemCell*) currentObject; break; } } } cell.nameLabel.text = key.Name; cell.qtyLabel.text = [quantity stringValue]; return cell; }

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• Why do most Database developers hate Agile

  - by Calm Storm

  To me "Agile" methodology is a common-sense oriented approach and one that should likely be adopted for most software projects. I find that while a lot of Middle Tier Developers and Front End developers find it a very sensible project delivery model, plenty of Database developers (and good ones) seem to be totally against it. They are very keen on knowing the biggest picture and designing a database solution that will cater to that. They do not seem to like "Vertical striping" of a functionality. They would rather see the complete design document/feature document instead of concentrating on small user stories. Sarcasm aside, can someone realistically provide some insight as to why this mentality is prevalent? Especially DB devs? What would be a convincing argument against that?

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• C++ Why is the copy constructor implicitly called?

  - by ShaChris23

  Why is the Child class's copy constructor called in the code below? I mean, it automatically converts Base to Child via the Child copy constructor. The code below compiles, but shouldn't it not compile since I haven't provided bool Child::operator!=(Base const&)? class Base { }; class Child : public Base { public: Child() {} Child(Base const& base_) : Base(base_) { std::cout <<"should never called!"; } bool operator!=(Child const&) { return true; } }; void main() { Base base; Child child; if(child != base) std::cout << "not equal"; else std::cout << "equal"; }

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• Why this button doesn't cause triple postback?

  - by focus

  We have developed a page with a asp.net and debugging it accidentally we have discovered on our page button with the next code on onclik attribute onclick="__doPostBack('ctl00$FormPlace$m_userTaskMarkAsUnreadButton',''); __doPostBack('ctl00$FormPlace$m_userTaskMarkAsUnreadButton','');WebForm_DoPostBackWithOptions(new WebForm_PostBackOptions("ctl00$FormPlace$m_userTaskMarkAsUnreadButton", "", true, "", "", false, false))" It seems that the button do three postbacks but when we click it only cause on postback. With this code seems that de button will cause three postbacks!! We have try it with Internet Explorer and Firefox and the button only cause on postback always. Are browsers who avoid that the button do three postback ? Or Is Asp.net server who avoid the three postback? We don't understand why the button behaves correctly if onclick attribute has three call to do Postbacks. Thanks

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• Why does the android emulator camera stop unexpectedly?

  - by user490074

  I am using Android 2.2 (API Level 8). The camera is enabled in the manifest. When I try the camera icon provided by the emulator model, it runs for a few seconds showing a gray box moving around a black and white checkerboard, then dies with the error message: Sorry! The application Camera (process com.android.camera) has stopped unexpectedly. Please try again. Trying again, of course, doesn't help. I am using the provided emulator camera to compare behavior with a camera application I am working on. Why does the android emulator camera stop unexpectedly?

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• why arrayfun does NOT improve my struct array operation performance

  - by HaveF

  here is the input data: % @param Landmarks: % Landmarks should be 1*m struct. % m is the number of training set. % Landmark(i).data is a n*2 matrix old function: function Landmarks=CenterOfGravity(Landmarks) % align center of gravity for i=1 : length(Landmarks) Landmarks(i).data=Landmarks(i).data - ones(size(Landmarks(i).data,1),1)... *mean(Landmarks(i).data); end end new function which use arrayfun: function [Landmarks] = center_to_gravity(Landmarks) Landmarks = arrayfun(@(struct_data)... struct('data', struct_data.data - repmat(mean(struct_data.data), [size(struct_data.data, 1), 1]))... ,Landmarks); end %function center_to_gravity when using profiler, I find the usage of time is NOT what I expected: Function Total Time Self Time* CenterOfGravity 0.011s 0.004 s center_to_gravity 0.029s 0.001 s Can someone tell me why? BTW...I can't add "arrayfun" as a new tag for my reputation.

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• Why can i not rewrite parent class?

  - by latvian

  I want to rewrite core/adminthtml/block/widget/tabs.php class which is a super class for core/adminhtml/block/sales/order/view/tabs.php class. Here is config code for both scenarios: <blocks> <adminhtml> <rewrite> <sales_order_view_tabs>Jimmy_SalesAffil_Block_Widget_Tabs</sales_order_view_tabs> <widget_tabs>Jimmy_SalesAffil_Block_Widget_Tabs</widget_tabs> ..... </rewrite> </adminhtml> </blocks> While I am able to rewrite ...view/tabs.php, I am not able to rewrite the super class. Why? Is it possible? How?

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• Why are forward declarations necessary?

  - by user199421

  In languages like C# and Java there is no need to declare (for example) a class before using it. If I understand it correctly this is because the compiler does two passes on the code. In the first it just "collects the information available" and in the second one it checks that the code is correct. In C and C++ the compiler does only one pass so everything needs to be available at that time. So my question basically is why isn't it done this way in C and C++. Wouldn't it eliminate the needs for header files?

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• Why border of <th> not showing here?

  - by metal-gear-solid

  How to give style to <thead> only, not to <th>? Why border of th not showing http://jsfiddle.net/r8mA7/ <table> <thead style="border-top:10px solid red; background:yellow"> <tr><th style="border-top:10px solid green">Name</th></tr> </thead> <tbody> <tr><td>Bob</td></tr> <tr><td>Tom</td></tr> </tbody> </table>

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• Why doesn't this work? jquery javascript

  - by mars

  $(document).ready(function() { musicList = new array() counter = 0; if($(".rA, .trA, .dA, .hA").length > 0) { /*$(".rA, .trA, .dA, .hA").each(function(e){*/ $(".hA").each(function(e){ $.post("/index/audio/ajax.track", { id: $(this).attr("rel") }, function(data){ /*THIS DOESN'NT WORK */ musicList.push(data.file); /*THIS DOESN'NT WORK */ alert(data.file);/*this words*/ }, "json"); counter++; }); if(counter>0) { alert(counter); } } }); I don't see anything wrong with the code but I have no idea why it won't work I just spent 3 hours trying to get it to work

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• Why can't I read session variables

  - by Marty Goetz

  I have a c# .net web application. I create session variables but when I try to read them after I leave the page that they were created from I can't. Created on page 1 Session["UserName"] = "WhatEver"; Then I do Response.Redirect("~/whatever.aspx"); and try to read to read the session variable in the Page_Load method of the new page string userName = Session["UserName"].ToString(); I receive "Object reference not set to an instance of an object." Why am I receiving this error and what can I do to fix the problem? I would greatly appreciate any help anyone can give me.

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• Why does Windows Explorer search freeze when I have an unrelated program paused in a debugger

  - by Evgeny

  While debugging my program, whether it's an ASP.NET application or a .NET console EXE and I have the debugger paused at a breakpoint I try to find a file in Windows Explorer. Either pressing WinKey+F or selecting search from the context menu freezes Windows Explorer - until I resume the program being debugged. My program has nothing to do with Windows Explorer! In fact, this happens in Visual Studio 2008 even with the simplest console EXE (WriteLine and ReadLine). I can't repro it with this simple EXE in WinDbg, but it does happen in with WinDb debugging an ASP.NET app. Why does this happen and how do I fix it? It's bloody annoying, especially when you don't realise what's going on. This is on Windows XP x64 SP2, running a .NET 3.5 application.

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• Why are my \n not working in PHP?

  - by Doug

  I'm playing with SAX and noticed it's not line breaking properly. I have no iea why. function flush_data() { global $level, $char_data; $char_data = trim($char_data); if( strlen( $char_data ) > 0 ) { print "\n"; $data = split("\n", wordwrap($char_data, 76 - ($level*2))); foreach($data as $line) { print str_repeat(' ', ($level +1)) . "[".$line."]"."\n"; } } $char_data = ''; }

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• Why MSVS Create lib file every time?

  - by codevania

  The problem is that Visual Stuiod re-create lib everytime. How can I make MSVS does not re-create? I don't know why MSVS create some kind of project's "lib" file whenever I press F5 to debug application. I just converted a solution file from 2005 to 2010. And this problem is occured. [ Revival ] 1.Build solution. 2.Debug 3.Stop debug 4.No source code change 5.Debug (re-create lib) I think that re-creation lib is not necessary. Re-creation lib file takes just a second. But it is little annoying. I'm in desperate need of your help.

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• Why do date manipulation in Java with milliseconds?

  - by staticsan

  I was recently faced with the problem of calculating the number of days from two dates in Java (without using joda, I'm afraid). Searching on the 'net shows most answers to this question say to get the milliseconds of the two days and convert that to days, which I found appalling. However, a scant few show a different approach: use a temporary variable to count how many times it takes adding 1 day to the first date to get to the second. This leaves the conversions to the code that does it best: the library. Why do so many people advocate the first? In another project, I had previously encountered numerous subtle date calculation problems involving time-zones, daylight-saving and once even leap years using seconds to do date comparisions and calculations. All these went away when all the comparison and calculation code was rewitten to use the language libraries. (This was in PHP, though, where the libraries are structured quite differently to Java.) So I'm understandably reluctant to use this "common wisdom" in the world of Java about comparing dates.

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