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• File.Copy with opened stream not crashing. Know why?

  - by Carlo

  I have this code, I open a stream (without closing or disposing it), then I copy the file used by the stream, I thought I should get a "Process can't access file somefile.xml because it's being used by another process" exception, but I don't. Any idea why? Thanks! The code: StreamWriter writer = new StreamWriter("C:\\somefile.xml"); writer.Write(string.Empty); // I thought this should crash since a stream is using "C:\somefile.xml" File.Copy("C:\\somefile.xml", "C:\\copy of somefile.xml", true);

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• Why Is It That Generics Constraint Can't Be Casted to Its Derived Type?

  - by Ngu Soon Hui

  It is quite puzzling to find out that Generics Constraint Can't Be Casted to Its Derived Type. Let's say I have the following code: public abstract class BaseClass { public int Version { get { return 1; } } public string FixString { get; set; } public BaseClass() { FixString = "hello"; } public virtual int GetBaseVersion() { return Version; } } public class DeriveClass: BaseClass { public new int Version { get { return 2; } } } And guess what, this method will return a compilation error: public void FreeConversion<T>(T baseClass) { var derivedMe = (DeriveClass)baseClass; } I would have to cast the baseClass to object first before I can cast it to DerivedClass. Seems to me pretty ugly. Why this is so?

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• Hibernate - why use many-to-one to represent a one-to-one?

  - by aberrant80

  I've seen people use many-to-one mappings to represent one-to-one relationships. I've also read this in a book by Gavin King and on articles. For example, if a customer can have exactly one shipping address, and a shipping address can belong to only one customer, the mapping is given as: <class name="Customer" table="CUSTOMERS"> ... <many-to-one name="shippingAddress" class="Address" column="SHIPPING_ADDRESS_ID" cascade="save-update" unique="true"/> ... </class> The book reasons as (quoting it): "You don't care what's on the target side of the association, so you can treat it like a to-one association without the many part." My question is, why use many-to-one and not one-to-one? What is it about a one-to-one that makes it a less desirable option to many-to-one? Thanks.

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• why does the array doesn't get initialized by global variable , even though it should not?

  - by ashish yadav

  why does the array a does not get initialized by global variable 'size'. include int size=5; int main() { int a[size]={1,2,3,4,5}; printf("%d",a[0]); return 0; } the compilation error is shown as "variable-sized object may not be initialized". according to me the array should get initialized by 'size'. i apologize if i am not clear but i feel i have expressed myself well enough. thank you!!!!!!!!!!!

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• Why are C, C++, and LISP so prevalent in embedded devices and robots?

  - by David

  It seems that the software language skills most sought for embedded devices and robots are C, C++, and LISP. Why haven't more recent languages made inroads into these applications? For example, Erlang would seem particularly well-suited to robotic applications, since it makes concurrent programming easier and allows hot swapping of code. Python would seem to be useful, if for no other reason than its support of multiple programming paradigms. I'm even surprised that Java hasn't made a foray into general robotic programming. I'm sure one argument would be, "Some newer languages are interpreted, not compiled" - implying that compiled languages are quicker and use fewer computational resources. Is this still the case, in a time when we can put a Java Virtual Machine on a cell phone or a SunSpot? (and isn't LISP interpreted anyway?)

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• Why does Google Page-Speed say that elements need compressing, when they already are compressed?

  - by Peter Snow

  My page is compressed using the following in .htaccess <ifModule mod_gzip.c> mod_gzip_on Yes mod_gzip_dechunk Yes mod_gzip_item_include file \.(html?|txt|css|js|php|pl)$ mod_gzip_item_include handler ^cgi-script$ mod_gzip_item_include mime ^text/.* mod_gzip_item_include mime ^application/x-javascript.* mod_gzip_item_exclude mime ^image/.* mod_gzip_item_exclude rspheader ^Content-Encoding:.*gzip.* </ifModule> Yslow says that the page and specifically the elements which Page-Speed is complaining about, are compressed and it gives the page an overall score of 90/100. Why then, does Page-Speed say that Compressing the following resources with gzip could reduce their transfer size by 118.8KiB (70% reduction). and it gives the page an overall score of 33/100?

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• Why jquery.animate on a textarea make the blinking cursor disapears?

  - by Tom S.

  Hello everyone. I have the following code $(document).ready(function() { $("#myTextArea").focus(function() { $("#myTextArea").animate({ "height": "75px"}, "normal"); return false; }); to expand a textbox when it gets focus. The expand occurs, however the blinking cursor disapears, at least in Firefox! Edited: The textarea is still focused, and i can type on it. Why does this happen? Is there a way to show it again? Thanks in advance

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• Can anyone explain why this behaviour might be happening in Windows Forms?

  - by gizgok

  I'm developing a Windows Forms Application. See attached image for the Interface. Now I've put a close button (X) in the Panel(say Panel2) which has Application Constants as label.The first combo box is in another panel(say Panel1). Now when I click on the X button in Panel 2 I want the Panel to be invisible and the combo box text to be blank. Simple enough. So I write Panel2.visible=false; comboBox1.SelectedIndex=-1; When I click on X, the text in combo box goes blank, then I have to click again for the Panel2 to go invisible. Then I changed the sequence comboBox1.SelectedIndex=-1; Panel2.visible=fasle; and this works smooth. Not sure why this might be happening? Is there anything that I might be doing with my form design/code to have such a behaviour?

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• Why am I not getting correct result when I calculate exponent with ^ in C++?

  - by xbonez

  I am using Bode's formuala to calculate distance of nth planet from sun dist = (4 + 3*(2^(n-2)))/10 If I calculate the distance this way, I get the right values: dist[2] = ((4 + 3*1)/10.0) ; dist[3] = ((4 + 3*2)/10.0) ; dist[4] = ((4 + 3*4)/10.0) ; But doing it this way, gives me incorrect values: vector <double> dist(5); for (unsigned int i = 2; i < 5; i++) { dist[i] = ((4 + 3*(2^(3-2)))/10.0) ; } Why so?

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• why doesn't perl sort the hash key in numeric order ?

  - by Haiyuan Zhang

  #!/usr/bin/perl use strict; use warnings; my %hash; foreach ( 1 .. 10 ) { $hash{$_} = $_; } foreach ( sort(keys %hash) ) { print $_ . ": " . "$hash{$_}" . "\n" ; } execute the above code, the result is as below : 1: 1 10: 10 2: 2 3: 3 4: 4 5: 5 6: 6 7: 7 8: 8 9: 9 Yes, I expect "10: 10" to be the last one taht is printed . So I just need someone to explain why perl give me surprise in this case.

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• Why does ElapsedTicks X 10 000 not equal ElapsedMilliseconds for .Net's Stopwatch?

  - by uriDium

  I am trying to performance test some code. I am using a stopwatch. When I output the number of milliseconds it always tells me 0 so I thought that I would try the number of ticks. I am seeing that the number of ticks is about 20 000 to 30 000. Looking at the MSDN at TimeSpan.TicksPerMillisecond it says that is 10 000 ticks per millisecond. In that case why are the elapsed milliseconds on my stopwatch not appearing as 2 or 3? What am I missing? I have even outputed the result on the same line. This is what I get. Time taken: 26856 ticks, 0 ms And it is constant.

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• How to figure out why ssh session does not exit sometimes?

  - by WilliamKF

  I have a C++ application that uses ssh to summon a connection to the server. I find that sometimes the ssh session is left lying around long after the command to summon the server has exited. Looking at the Centos4 man page for ssh I see the following: The session terminates when the command or shell on the remote machine exits and all X11 and TCP/IP connections have been closed. The exit status of the remote program is returned as the exit status of ssh. I see that the command has exited, so I imagine not all the X11 and TCP/IP connections have been closed. How can I figure out which of these ssh is waiting for so that I can fix my summon command's C++ application to clean up whatever is being left behind that keeps the ssh open. I wonder why this failure only occurs some of the time and not on every invocation? It seems to occur approximately 50% of the time. What could my C++ application be leaving around to trigger this?

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• Why is it so hard to build a gtk programe without console using cmake in windows?

  - by Runner

  I'm following the tuto: http://zetcode.com/tutorials/gtktutorial/firstprograms/ It works but each time I double click on the executable,there is a console which I don't want it there. How do I get rid of that console? I tried this: add_executable(Cmd WIN32 cmd.c) But got this fatal error: MSVCRTD.lib(crtexew.obj) : error LNK2019: unresolved external symbol _WinMain@16 referenced in function ___tmainCRTStartup Cmd.exe : fatal error LNK1120: 1 unresolved externals While using gcc directly works: gcc -o Cmd cmd.c -mwindows .. I'm guessing it has something to do with the entry function: int main( int argc, char *argv[]),but why gcc works? How can I make it work with cmake?

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• C# - Why can't I enforce derived classes to have parameterless constructors?

  - by FrisbeeBen

  I am trying to do the following: public class foo<T> where T : bar, new { _t = new T(); private T _t; } public abstract class bar { public abstract void someMethod(); // Some implementation } public class baz : bar { public overide someMethod(){//Implementation} } And I am attempting to use it as follows: foo<baz> fooObject = new foo<baz>(); And I get an error explaining that 'T' must be a non-abstract type with a public parameterless constructor in order to use it as parameter 'T' in the generic type or method. I fully understand why this must be, and also understand that I could pass a pre-initialized object of type 'T' in as a constructor argument to avoid having to 'new' it, but is there any way around this? any way to enforce classes that derive from 'bar' to supply parameterless constructors?

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• Why doesn't C++ allow you to request a pointer to the most derived class?

  - by Matthew Lowe

  (This question should probably be answered with a reference to Stroustrup.) It seems extremely useful to be able to request a pointer to the most derived class, as in the following: class Base { ... }; class DerivedA { ... }; class DerivedB { ... }; class Processor { public: void Do(Base* b) {...} void Do(DerivedA* d) {...} void Do(DerivedB* d) {...} }; list<Base*> things; Processor p; for(list<Base*>::iterator i=things.begin(), e=things.end(); i!=e; ++i) { p.Do(CAST_TO_MOST_DERIVED_CLASS(*i)); } But this mechanism isn't provided in c++. Why?

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• Why do so many mathematicians format code so poorly? [closed]

  - by marcog

  I have done a fair amount of programming together with mathematicians. Now I am even teaching some high school kids coming from a mathematics background how to program. Most of these people format their code so hideously it's hard to believe. I've even worked with and taught mathematicians who will fight the auto-indenter! Why is this so common amongst mathematicians? BTW, this is one reason I have started teaching Python. Yet still they find ways other than indentation to produce whacked coding styles!

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• Why this code does not do what I mean?

  - by Mike

  $w = 'self-powering'; %h = (self => 'self', power => 'pau?', ); if ($w =~ /(\w+)-(\w+)ing$/ && $1~~%h && $2~~%h && $h{$2}=~/?$/) { $p = $h{$1}.$h{$2}.'ri?'; print "$w:"," [","$p","] "; } I expect the output to be self-powering: selfpau?ri? But what I get is: self-powering: [ri?] My guess is something's wrong with the code $h{$2}=~/?$/ It seems that when I use $h{$2}!~/?$/ Perl will do what I mean but why I can't get "self-powering: selfpau?ri?"? What am I doing wrong? Any ideas? Thanks as always for any comments/suggestions/pointers :)

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• Why does Java return a date in GMT-4.5 when choosing Co-ordinated Universal Time time zone in Window

  - by Simon Nickerson

  We have seen a strange issue on some Windows XP machines involving the "Co-ordinated Universal Time" time zone. Not all Windows XP machines seem to have it, but on those that do, the following simple Java program public class TimeTest { public static void main(String[] args) { System.out.println(java.util.TimeZone.getDefault()); System.out.println(new java.util.Date()); } } on JDK 1.6.0_06 prints: sun.util.calendar.ZoneInfo[id="America/Caracas",offset=-16200000,dstSavings=0,useDaylight=false,transitions=5,lastRule=null] Fri Nov 13 05:34:14 VET 2009 (i.e. 4 and a half hours behind GMT). I should add that I am based in London, and have never been to South America. :-) My questions are: Where does Java get this time zone from? I thought Co-ordinated Universal Time was supposed to be the new name for GMT. Why do some Windows machines have this time zone but not others?

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• Why does a Linq Cast<T> operation fail when I have an implicit cast defined?

  - by Ryan Versaw

  I've created two classes, with one of them having an implicit cast between them: public class Class1 { public int Test1; } public class Class2 { public int Test2; public static implicit operator Class1(Class2 item) { return new Class1{Test1 = item.Test2}; } } When I create a new list of one type and try to Cast<T> to the other, it fails with an InvalidCastException: List<Class2> items = new List<Class2>{new Class2{Test2 = 9}}; foreach (Class1 item in items.Cast<Class1>()) { Console.WriteLine(item.Test1); } This, however, works fine: foreach (Class1 item in items) { Console.WriteLine(item.Test1); } Why is the implicit cast not called when using Cast<T>?

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• Why are my JavaScript variables not persisting across functions?

  - by Eric Belair

  I have the following JavaScript in my HTML page referencing an HTML form on the page: <script type="text/javascript"> <!-- var myForm = document.myForm; function validateForm() { if (myForm.myInput == "") alert("Please input some text."); return false; } myForm.submit(); } function showFormInput() { myForm.reset(); document.getElementById('myInput').style.display = 'inline'; } //--> </script> ... <form name="myForm" id="myForm" action="..." method="post"> <input id="myInput" name="myInput" type="text" value="" style="display:none;" /> </form> Both functions are throwing an exception when trying to access the variable myForm, saying that "myForm is null or not an object". Why is this occurring?

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• Why the valid looking statement gives error in MATLAB?

  - by user198729

  It's from this question? Why the two solutions doesn't work, though it looks very valid for me: >> t = -pi:0.1:pi; >> r = ((sin(t)*sqrt(cos(t)))*(sin(t) + (7/5))^(-1)) - 2*sin(t) + 2 ; ??? Error using ==> mtimes Inner matrix dimensions must agree. >> t = -pi:0.1:pi; >> r = ((sin(t).*sqrt(cos(t))).*(sin(t) + (7/5)).^(-1)) - 2*sin(t) + 2 ; >> plot(r,t) ??? Error using ==> plot Vectors must be the same lengths. What's wrong with the above?

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• Why does schema.rb change (in the eyes of Git) when just running rake db:migrate?!

  - by erskingardner

  This is a little general I know, but it's been bugging the hell out of me. I've been working on lots of rails projects remotely with Git and every time I do a git pull and see that there is some sort of data change (migration, or schema.rb change) I do a rake db:migrate. These generally run fine and I can continue working. But if you do a git pull and then git status, your working directory is clean (obviously) then do a rake db:migrate (obviously when there are changes) and another git status and all the sudden your db/schema.rb has changed. I have been just doing a git checkout immediately to reset back to the latest committed version of the schema.rb file, but why should this be necessary?! What is rails doing? Updating a timestamp? I can't seem to figure out what the diff is but maybe I'm just missing something?

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• Why is super.super.method(); not allowed in Java?

  - by Tim Büthe

  I read this question and thought that would easily be solved (not that it isn't solvable without) if one could write: @Override public String toString() { return super.super.toString(); } I'm not sure if it is useful in many cases, but I wonder why it isn't and if something like this exists in other languages. What do you guys think? EDIT: To clarify: yes I know, that's impossible to at to Java and I don't really miss it. This is nothing I expected to work and was surprised getting a compiler error. I just had the idea and like to discuss it.

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• Why learn Perl, Python, Ruby if the company is using C++, C# or Java as the application language?

  - by szabgab

  I wonder why would a C++, C#, Java developer want to learn a dynamic language? Assuming the company won't switch its main development language from C++/C#/Java to a dynamic one what use is there for a dynamic language? What helper tasks can be done by the dynamic languages faster or better after only a few days of learning than with the static language that you have been using for several years? Update After seeing the first few responses it is clear that there two issues. My main interest would be something that is justifiable to the employer as an expense. That is, I am looking for justifications for the employer to finance the learning of a dynamic language. Aside from the obvious that the employee will have broader view, the employers are usually looking for some "real" benefit.

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• Why are these strings escaping from my regular expression in python?

  - by dohkoxar

  In my code, I load up an entire folder into a list and then try to get rid of every file in the list except the .mp3 files. import os import re path = '/home/user/mp3/' dirList = os.listdir(path) dirList.sort() i = 0 for names in dirList: match = re.search(r'\.mp3', names) if match: i = i+1 else: dirList.remove(names) print dirList print i After I run the file, the code does get rid of some files in the list but keeps these two especifically: ['00. Various Artists - Indie Rock Playlist October 2008.m3u', '00. Various Artists - Indie Rock Playlist October 2008.pls'] I can't understand what's going on, why are those two specifically escaping my search.

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