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• Why does casting to double using "String * 1" fail? Will CDbl(String) work on all systems?

  - by Jamie Bull

  I have an application which contains the line below to assign a parsed XML value to a variant array. V(2) = latNode.Text * 1 This works fine on my system (Windows 7, Excel 2010) but doesn't work on some other system or systems - and I've not been able to get a response from the user who reported the problem. I've switched out the offending line for: V(2) = CDbl(latNode.Text) This still works on my system, but then I had no problem in the first place. The question is on what systems does the first approach fail and why, and will the second method always work? I'm sure I've used the "Stying * 1" trick elsewhere before and would like to know how concerned I should be about tracking down other occurrences. Thanks.

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• Why are Java primitive types' modifiers `public`, `abstract`, & `final`?

  - by oconnor0

  In the process of doing some reflection on Java types, I came across an oddity that I do not understand. Inspecting int for its modifiers returns public, abstract, and final. I understand public and final, but the presence of abstract on a primitive type is non-obvious to me. Why is this the case? Edit: I am not reflecting on Integer but on int: import java.lang.reflect.Modifier; public class IntegerReflection { public static void main(final String[] args) { System.out.println(String.format("int.class == Integer.class -> %b", int.class == Integer.class)); System.out.println(String.format("int.class modifiers: %s", Modifier.toString(int.class.getModifiers()))); System.out.println(String.format("Integer.class modifiers: %s", Modifier.toString(Integer.class.getModifiers()))); } } The output when run: int.class == Integer.class -> false int.class modifiers: public abstract final Integer.class modifiers: public final

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• Why timed lock doesnt throws a timeout exception in C++0x?

  - by Vicente Botet Escriba

  C++0x allows to lock on a mutex until a given time is reached, and return a boolean stating if the mutex has been locked or not. template <class Clock, class Duration> bool try_lock_until(const chrono::time_point<Clock, Duration>& abs_time); In some contexts, I consider an exceptional situation that the locking fails because of timeout. In this case an exception should be more appropriated. To make the difference a function lock_until could be used to get a timeout exception when the time is reached before locking. template <class Clock, class Duration> void lock_until(const chrono::time_point<Clock, Duration>& abs_time); Do you think that lock_until should be more adequate in some contexts? if yes, on which ones? If no, why try_lock_until will always be a better choice?

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• When and why does an EventHandler require objects to be final?

  - by Michiel Borkent

  I have the following code from a GWT Project that is part of the onModuleLoad() method (similar to Java's main method, if you don't know GWT): final TextBox t1 = new TextBox(); final Label lt1 = new Label(); t1.addKeyUpHandler(new KeyUpHandler() { @Override public void onKeyUp(KeyUpEvent event) { // TODO Auto-generated method stub if (!(t1.getText().matches("\\w{2}-\\w{2}-\\w{2}"))) lt1.setText("Invalid."); else lt1.setText("OK."); } }); Why do the two local variables have to be final here?

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• Why is this Scala example of implicit paremeter not working?

  - by Alex R

  simple REPL test... def g(a:Int)(implicit b:Int) = {a+b} Why do neither of these attempted usages work? 1. scala class A { var b:Int =8; var c = g(2) } :6: error: could not find implicit value for parameter b: Int class A { var b:Int =8; var c = g(2) } 2. scala class A(var b:Int) { var c = g(2) } :6: error: could not find implicit value for parameter b: Int class A(var b:Int) { var c = g(2) } ^ Thanks

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• Haskell: Why is it saying my function type is off?

  - by linkmaster03

  I wrote a little Haskell program to find the area of a triangle, primarily to practice custom types, but it keeps throwing the following error on compile: areafinder.hs:7:4: Couldn't match expected type 'Triangle' against inferred type 'm b' In a stmt of a 'do' expression: putStr "Base: " In the expression: do { putStr "Base: "; baseStr I'm not sure where 'm b' comes from, so I'm at a loss here. Why is it throwing this error, and what can I do to fix it? Here is my code: module Main where data Triangle = Triangle Double Double -- base, height getTriangle :: Triangle getTriangle = do putStr "Base: " baseStr Double calcTriangle (Triangle base height) = base * height main = putStrLn ("Area = " ++ show (calcTriangle getTriangle)) Thanks. :)

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• Why would a 'public event EventHandler cccc' be null?

  - by Matt

  Why would a 'public event EventHandler cccc' be null? I have a class that's public class Builder { public event EventHandler StartedWorking; public Builder() { // Constructor does some stuff } public void Start() { StartedWorking(this, eventargobject); //StartedWorking is null -- } } This seems straightforward and something I do all the time? Am I missing something obvious or is there something that could cause this? EDIT: Does this mean that if I fire an event that is not subscribed to in a client class I have to check that it is not null? EDIT-2: I guess I'd never had events that were never not subscribed to and hence never ran into this -- You learn something new every day Sorry about the seemingly stupid question....

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• Why is selecting specified columns, and all, wrong in Oracle SQL?

  - by TomatoSandwich

  Say I have a select statement that goes.. select * from animals That gives a a query result of all the columns in the table. Now, if the 42nd column of the table animals is is_parent, and I want to return that in my results, just after gender, so I can see it more easily. But I also want all the other columns. select is_parent, * from animals This returns ORA-00936: missing expression. The same statement will work fine in Sybase, and I know that you need to add a table alias to the animals table to get it to work ( select is_parent, a.* from animals ani), but why must Oracle need a table alias to be able to work out the select?

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• Why does SQL Server 2000 treat SELECT test.* and SELECT t.est.* the same?

  - by Chris Pebble

  I butter-fingered a query in SQL Server 2000 and added a period in the middle of the table name: SELECT t.est.* FROM test Instead of: SELECT test.* FROM test And the query still executed perfectly. Even SELECT t.e.st.* FROM test executes without issue. I've tried the same query in SQL Server 2008 where the query fails (error: the column prefix does not match with a table name or alias used in the query). For reasons of pure curiosity I have been trying to figure out how SQL Server 2000 handles the table names in a way that would allow the butter-fingered query to run, but I haven't had much luck so far. Any sql gurus know why SQL Server 2000 ran the query without issue? Update: The query appears to work regardless of the interface used (e.g. Enterprise Manager, SSMS, OSQL) and as Jhonny pointed out below it bizarrely even works when you try: SELECT TOP 1000 dbota.ble.* FROM dbo.table

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• Why do i get segfault at the end of the application after everything's beed done properly ?

  - by VaioIsBorn

  #include <string.h> #include <stdlib.h> #include <stdio.h> int main(void) { unsigned char *stole; unsigned char pass[] = "m4ak47"; printf("Vnesi password: \t"); scanf("%s", stole); if(strncmp(stole, pass, sizeof(pass)) != 0) { printf("wrong password!\n"); exit(0); } else printf("Password correct\n"); printf("some stuf here...\n\n"); return 0; } This program is working nice, but with one problem - if the password is correct then it DOES do the printing of 'some stuf here...' but it also shows me segmentation fault error at the end. Why ?

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• Why does the :nth-child(2) selector work on what I expect to be :first-child?

  - by Ben

  I have an example of what I'm trying to ask. I use this kind of format often. I'd expect to be able to select that first div with fieldset div:first-child { } but it seems that it's only grabbed by the 2nd child selector. I would expect "field 1" to be red and not blue. It makes more sense semantically (to me at least) to say "style the first div in the fieldset like so" instead of saying the 2nd. Why is this happening and is there a way to achieve the effect I want (to be able to call div:first-child)?

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• Why a new instance uses logger from old instances?

  - by Roman

  I generate 2 instances in this way: gameManager manager1 = new CTManager(owner,players1,"en"); manager1.start(); gameManager manager2 = new CTManager(owner,players2,"en"); manager2.start(); The start() method of the gameManager looks like that: void start() { game.start(); } When I create the game instance I create a loger: log = Logger.getLogger("TestLog"); (log is a public field of the class in which the game belongs). In the game.start() I run many processes and give them a reference to the corresponding log. So, I expect that manager1 and manager2 will write to different files. But manager2 writes to its own file and to the log file of the manager1. Why can it happen?

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• Why am I getting a Java NoSuchPortException when the port exists?

  - by user258526

  Got the following production code below, I'm using it for a new driver. portName is COM4 and this port exists on the PC (and I can connect to it with hyperterminal), so why does Javacomm throw a NoSuchPortException? COM4 shows up fine in device mgr. too final String portName = getSerialPort(); try { final CommPortIdentifier id = CommPortIdentifier.getPortIdentifier(portName); port = (SerialPort) id.open(getName(), 1000); } catch (NoSuchPortException nspe) { report(SeverityCode.LEVEL2, getName(), "PIN Pad is not connected to " + portName + " port, or the port does not exist."); return; } catch (PortInUseException piue) { report(SeverityCode.LEVEL2, getName(), portName + " port is already in-use by some other device. Reason: " + piue.getMessage()); return; }

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• Why isn't the eigenclass equivalent to self.class, when it looks so similar?

  - by The Wicked Flea

  I've missed the memo somewhere, and I hope you'll explain this to me. Why is the eigenclass of an object different from self.class? class Foo def initialize(symbol) eigenclass = class << self self end eigenclass.class_eval do attr_accessor symbol end end end My train of logic that equates the eigenclass with class.self is rather simple: class << self is a way of declaring class methods, rather than instance methods. It's a shortcut to def Foo.bar. So within the reference to the class object, returning self should be identical to self.class. This is because class << self would set self to Foo.class for definition of class methods/attributes. Am I just confused? Or, is this a sneaky trick of Ruby meta-programming?

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• Why do virtual memory addresses for linux binaries start at 0x8048000?

  - by muteW

  Disassembling an ELF binary on a Ubuntu x86 system I couldn't help but notice that the code(.text) section starts from the virtual address 0x8048000 and all lower memory addresses seem to be unused. This seems to be rather wasteful and all Google turns up is either folklore involving STACK_TOP or protection against null-pointer dereferences. The latter case looks like it can be fixed by using a single page instead of leaving a 128MB gap. So my question is this - is there a definitive answer to why the layout has been fixed to these values or is it just an arbitrary choice?

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• Assembly: Why does jumping to a label that returns via ret cause a segmentation fault?

  - by Terribad

  Linux Assembly Tutorial states: there is one very important thing to remember: If you are planning to return from a procedure (with the RET instruction), don't jump to it! As in "never!" Doing that will cause a segmentation fault on Linux (which is OK – all your program does is terminate), but in DOS it may blow up in your face with various degrees of terribleness. But I cannot understand why does it causes a segmentation fault. it sounds just like returning from a function. I have a situation where I need to implement the logic "If X happens, call procedure A. Otherwise, call procedure B." Is there any other way than jumping around like a kangaroo weaving spaghetti code?

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• iOS Development: Why isn't my try block catching the exception?

  - by BeachRunnerJoe

  Hi. I have an exception being thrown in my code, but when I wrap it in an try/catch block, it doesn't get caught. The NSLog statement is never called in the catch block. Here's the code... NSInteger quoteLength; [data getBytes:(void *)&quoteLength range:NSMakeRange(sizeof(messageType), sizeof(quoteLength))]; @try { //Debugger stack trace shows an NSException being thrown on this statement NSData *stringData = [data subdataWithRange:NSMakeRange(sizeof(messageType) + sizeof(quoteLength), [data length])]; NSString *quote = [[NSString alloc] initWithData:stringData encoding:NSUTF8StringEncoding]; NSLog(@"received quote: %@",quote); [quote release]; } @catch (NSException * e) { NSLog(@"Exception Raised: %@", [e reason]); } Why doesn't it get caught? Thanks so much!

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• Why do I get the error "X is not a member of Y" even though X is a friend of Y?

  - by user1232138

  I am trying to write a binary tree. Why does the following code report error C2039, "'<<' : is not a member of 'btree<T'" even though the << operator has been declared as a friend function in the btree class? #include<iostream> using namespace std; template<class T> class btree { public: friend ostream& operator<<(ostream &,T); }; template<class T> ostream& btree<T>::operator<<(ostream &o,T s) { o<<s.i<<'\t'<<s.n; return o; }

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• Can you tell me why my webpage displays differently in IE and how to fix it.

  - by b-rad

  I've been browsing through all of the CSS related cross-browser questions trying to troubleshoot my IE styling issues with no luck. Can anyone tell me how to fix my homepage styles so that it displays the same in IE as it currently does in Firefox? I've used Firebug (probably why it looks good in Firefox) but I can't find any tools for IE that will let me change the stylesheet real time. I'm just as interested in the process of figuring out this answer as I am in the answer itself so posting the steps you took to figure it out would be beneficial. (want to be able to do this myself next time!!!) Website is AppQandA.com. Scroll down to the bottom in IE and notice the footer. It's not like this on every page.....just the main page and the questions page.

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• Why is Rake not able to invoke multiple tasks consecutively?

  - by PandaWood

  I have a Rake task which I have simplified below. I'm using Ruby 1.9 on Windows. Perhaps you would like to guess the outcome of calling the Rake task "list_all_levels" below? It should be: "Hello level 1" "Hello level 2" "Hello level 3" But for reasons unknown to me, it prints only "Hello level 1" and then stops. That is, it always invokes only the first task. If I change the first line to pass the arg "42", it would print "Hello level 42" and then stop. I'm wondering why does it not invoke the task 3 times and print all 3 lines? And is there any way to get it to work how I would expect? task :list_all_levels => [] do Rake::Task[:list].invoke 1 Rake::Task[:list].invoke 2 Rake::Task[:list].invoke 3 end task :list, [:level] => [] do |t, args| puts "Hello level #{args.level}" end

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• Why does GetExportedValues<T>() no longer work after using the .net 4 final version of MEF?

  - by BigJason

  I have been developing a managed extensibility framework application for the last several months using the community preview. I have been using the GetExportedValues() method and the PartCreationPolicy(CreationPolicy.NonShared) to fake a class factory (since only the silverlight version supports a factory). This was working great until I upgraded the project to use .net 4.0. There is no error, it just doesn't work. So why did this code stop working? The code follows: The factory method: public static IEnumerable<DataActionBase> GetActionsFromDirectory(string PluginsFolder) { IEnumerable<DataActionBase> result = null; var catalog = new DirectoryCatalog(PluginsFolder); var container = new CompositionContainer(catalog: catalog); result = container.GetExportedValues<DataActionBase>(); return result; } Example Export Class: [Export(typeof(DataActionBase))] [PartCreationPolicy(CreationPolicy.NonShared)] public class AnAction : DataActionBase { .... }

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• why is the Border bigger than the Group in this case?

  - by user273895

  if I place a Border with width and height of "100%" inside a Group with width and height of 10 pixels the Border looks bigger than 10 pixels, why? <s:Application xmlns:fx="http://ns.adobe.com/mxml/2009" xmlns:s="library://ns.adobe.com/flex/spark" xmlns:mx="library://ns.adobe.com/flex/halo" > <s:Group width="10" height="10"> <s:Border width="100%" height="100%" borderColor="#FF0000"/> </s:Group> </s:Application>

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• Why PHP (script) serves more requests than CGI (compiled)?

  - by Lucas Batistussi

  I developed the following CGI script and run on Apache 2 (http://localhost/test.chtml). I did same script in PHP (http://localhost/verifica.php). Later I performed Apache benchmark using Apache Benchmark tool. The results are showed in images. include #include <stdlib.h> int main(void) { printf("%s%c%c\n", "Content-Type:text/html;charset=iso-8859-1",13,10); printf("<TITLE>Multiplication results</TITLE>\n"); printf("<H3>Multiplication results</H3>\n"); return 0; } Someone can explain me why PHP serves more requests than CGI script?

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• Why can I create a table with PRIMARY KEY on a nullable column?

  - by AlexKuznetsov

  The following code creates a table without raising any errors: CREATE TABLE test( ID INTEGER NULL, CONSTRAINT PK_test PRIMARY KEY(ID) ) Note that I cannot insert a NULL, as expected: INSERT INTO test VALUES(1),(NULL) ERROR: null value in column "id" violates not-null constraint DETAIL: Failing row contains (null). ********** Error ********** ERROR: null value in column "id" violates not-null constraint SQL state: 23502 Detail: Failing row contains (null). Why can I create a table with a self-contradictory definition? ID column is explicitly declared as NULLable, and it is implicitly not nullable, as a part of the PRIMARY KEY. Does it make sense? Edit: would it not be better if this self-contradictory CREATE TABLE just failed right there?

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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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