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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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• Microsoft Access - Enter Parameter Value why?

  - by Jane Doe

  I am encountering a problem for my database. Here is the relationships of the database And tried to do the query for how many transactions have movie "Harry_Potter"? so I used SQL query: SELECT COUNT(td.movie) AS number_of_occurrence, td.transaction_number FROM TransactionDetails td, MovieDetails md WHERE md.movie = Harry_Potter But it asks for Harry_Potter enter parameter value why? The relevant SQL statements are CREATE TABLE TransactionDetails ( transaction_number INTEGER PRIMARY KEY, movie VARCHAR(30) NOT NULL, date_of_transaction DATE NOT NULL, member_number INTEGER NOT NULL ) CREATE TABLE MovieDetails ( movie VARCHAR(30) PRIMARY KEY, movie_type VARCHAR(3) NOT NULL, movie_genre VARCHAR(10) NOT NULL ) ALTER TABLE TransactionDetails ADD CONSTRAINT member_number_fk FOREIGN KEY (member_number) REFERENCES LimelightMemberDetails(member_number); ALTER TABLE TransactionDetails ADD CONSTRAINT transaction_number_drink_fk FOREIGN KEY (transaction_number) REFERENCES DrinkTransactionDetails(transaction_number); ALTER TABLE TransactionDetails ADD CONSTRAINT transaction_number_food_fk FOREIGN KEY (transaction_number) REFERENCES FoodTransactionDetails(transaction_number); ALTER TABLE TransactionDetails ADD CONSTRAINT movie_fk FOREIGN KEY (movie) REFERENCES MovieDetails (movie); Thank you for your help! If there is anything wrong with my database design please let me know! thank you!

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• Navigationcontroller, why isnt this working?

  - by f0rz

  Hi ! Why wont this work? View1 loads View2. In view2: - (void) goToView { View3 *plainText = [[Tabview_testViewController alloc] initWithNibName:@"View3" bundle:nil]; [self.navigationController pushViewController:plainText animated: NO]; [plainText release]; } - (void)viewDidLoad { [self goToView]; [super viewDidLoad]; } This will not trigger navigationController to pushView, but if I add a button and setAction (goToView) it works perfectly. What kind of problem do I missing here? Regards

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• Why can't I do this from ASP.NET?

  - by Nissan Fan

  The code below spawns the process and sits forever, never finishing. It doesn't matter what process I run. Also, if I use Shell with Wait it does the same thing. If I set wait to false in either approach it works just fine. It's ASP.NET 2.0 VB.NET DotNetNuke 4.0 on Windows Server 2003. I can't even phathom why this would hang up. From: http://www.freevbcode.com/ShowCode.asp?ID=5879 Public Sub ShellandWait(ByVal ProcessPath As String) Dim objProcess As System.Diagnostics.Process objProcess = New System.Diagnostics.Process() objProcess.StartInfo.FileName = ProcessPath objProcess.StartInfo.WindowStyle = ProcessWindowStyle.Normal objProcess.Start() 'Wait until the process passes back an exit code objProcess.WaitForExit() 'Free resources associated with this process objProcess.Close() End Sub

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• Why do spaces appear in my string?

  - by Abs

  Hello all, I have this function below which returns all IDs of checked boxes on my page seperated by a comma. It works great but the problem is, it seems to put a lot of white space after each checkbox ID. I can't seem to figure out why? /*Returns selected checkbox ID in string seperated by comma */ function get_selected_chkbox(){ var checked_string = ''; $('#report_table').find("input[type='checkbox']").each(function(){ if(this.checked){ checked_string = checked_string + this.id + ','; } }); alert(checked_string);//test1 ,test2 , return checked_string; } Thanks all for any help

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• Why not System.Void?

  - by Stewart

  I have no practical reason for knowing this answer, but I'm curious anyway... In C#, trying to use System.Void will produce a compilation error: error CS0673: System.Void cannot be used from C# -- use typeof(void) to get the void type object As I understood it, void is simply an alias of System.Void. So, I don't understand why 'System.Void' can't be used directly as you might with 'string' for 'System.String' for example. I would love to read an explanation for this! Incidentally, System.Void can be successfully used with the Mono compiler, instead of Microsoft's .Net, and there it appears equivalent to using the void keyword. This must therefore be a compiler-enforced restriction rather than a CLR restriction, right?

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• Why self.view is not available

  - by amok

  I have this code in the main view controller and it is working just fine and as I wanted. loadingActionSheet = [[UIActionSheet alloc] initWithTitle:@"Posting To Twitter..." delegate:nil cancelButtonTitle:@"Cancel" destructiveButtonTitle:nil otherButtonTitles:nil]; [loadingActionSheet showInView:self.view]; I wanted that code to be reusable from different part of the project so I moved it in a separate file (UIView based). The poblem that I am facing is that self.view is not available there and I don't know why because I am learning and I don't know enough to understand what I am missing. What do I have to do/add/change to have the actionsheet shown in my current view even if that code lives somewhere else?

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• Why can't we have an immutable version of operator[] for map

  - by Yan Cheng CHEOK

  The following code works fine : std::map<int, int>& m = std::map<int, int>(); int i = m[0]; But not the following code : // error C2678: binary '[' : no operator... const std::map<int, int>& m = std::map<int, int>(); int i = m[0]; Most of the time, I prefer to make most of my stuff to become immutable, due to reason : http://www.javapractices.com/topic/TopicAction.do?Id=29 I look at map source code. It has mapped_type& operator[](const key_type& _Keyval) Is there any reason, why std::map unable to provide const mapped_type& operator[](const key_type& _Keyval) const

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• Why won't this static_cast in C++ work?

  - by samoz

  When I try to use a static_cast to cast a double* to an int*, I get the following error: invalid static_cast from type ‘double*’ to type ‘int*’ Here is the code: #include <iostream> int main() { double* p = new double(2); int* r; r=static_cast<int*>(p); std::cout << *r << std::endl; } I understand that there would be problems converting between a double and an int, but why is there a problem converting between a double* and an int*?

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• why cannot use uncaught_exception in dtor?

  - by camino

  Hi , Herb Sutter in his article http://www.gotw.ca/gotw/047.htm pointed out that we cannot use uncaught_exception in desturctor function, // Why the wrong solution is wrong // U::~U() { try { T t; // do work } catch( ... ) { // clean up } } If a U object is destroyed due to stack unwinding during to exception propagation, T::~T will fail to use the "code that could throw" path even though it safely could. but I write a test program, and T::~T in fact didn't use the "code that could throw" #include <exception> #include <iostream> using namespace std; class T { public: ~T() { if( !std::uncaught_exception() ) { cout<<"can throw"<<endl; throw 1; } else { cout<<"cannot throw"<<endl; } } }; struct U { ~U() { try { T t; } catch( ... ) { } } }; void f() { U u; throw 2; } int main() { try { f(); } catch(...) {} } output is : cannot throw did I miss something? Thanks

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• Why is memory management so visible in Java?

  - by Emil

  I'm playing around with writing some simple Spring-based web apps and deploying them to Tomcat. Almost immediately, I run into the need to customize the Tomcat's JVM settings with -XX:MaxPermSize (and -Xmx and -Xms); without this, the server easily runs out of PermGen space. Why is this such an issue for Java compared to other garbage collected languages? Comparing counts of "tune X memory usage" for X in Java, Ruby, Perl and Python, shows that Java has easily an order of magnitude more hits in Google than the other languages combined.

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• Why is this global variable not being changed???

  - by user398314

  Why does this turn up null instead of being set to the data returned from the ajax call? It must be something simple i am overlooking. var message; $(document).ready(function(){ fbFetchMessage(); alert(message); }); function fbFetchMessage(){ var url = "http://graph.facebook.com/companyname/feed?callback=?"; $.getJSON(url,function(json){ message = json.data[0].message; }); }

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• Index out of range, but why?

  - by Stuart

  I have a gridview, and i have a SelectedIndexChanged event on it... protected void GridView1_SelectedIndexChanged(object sender, EventArgs e) { GridViewRow Row = GridView1.SelectedRow; //do some stuff } Then i get an error... Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index I dont understand why, the Gridview is being binded in pageload. but not in post back... if (!IsPostBack) { GridView1.DataSource = UserAccounts; GridView1.DataBind(); }

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• Why SQL functions are faster than UDF

  - by Zerotoinfinite

  Though it's a quite subjective question but I feel it necessary to share on this forum. I have personally experienced that when I create a UDF (even if that is not complex) and use it into my SQL it drastically decrease the performance. But when I use SQL inbuild function they happen to work pretty faster. Conversion , logical & string functions are clear example of that. So, my question is "Why SQL in build functions are faster than UDF"? and it would be an advantage if someone can guide me how can I judge/manipulate function cost either mathematically or logically.

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• Why should "miter" joints be slower than others?

  - by Hanno Fietz

  I'm having a graphics problem on drawing lines in Flash Player, where two lines drawn on top of each other with different thickness don't align properly if I use any other JointStyle than MITER. For pictures of the effect, and for the graphics oriented part of the question, see my post over on doctype. However, there's also a second angle on this problem, which is: why should drawing the "mitered" joints be so much slower than others? This seems to be a problem since at least FP 8, but I couldn't find any detailed info on what the problem might be. Is this just an ordinary bug that didn't get fixed yet, or is there something inherently slower about drawing these joints? For example, they seem to have something to do with square roots, but I seriously lack understanding of what this joint style thing is all about, technically. It just looks like some minor detail a graphic designer might worry about. I'm asking because I'm wondering if I can do something to mitergate, er, mitigate, the problem.

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• Why is address zero used for null pointer?

  - by Joel

  In C (or C++ for that matter), pointers are special if they have the value zero: I am adviced to set pointers to zero after freeing their memory, because it means freeing the pointer again isn't dangerous; when I call malloc it returns a pointer with the value zero if it can't get me memory; I use if (p != 0) all the time to make sure passed pointers are valid etc. But since memory addressing starts at 0, isn't 0 just as a valid address as any other? How can 0 be used for handling null pointers if that is the case? Why isn't a negative number null instead?

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• Why is '\x' invalid in Python?

  - by Paul McGuire

  I was experimenting with '\' characters, using '\a\b\c...' just to enumerate for myself which characters Python interprets as control characters, and to what. Here's what I found: \a - BELL \b - BACKSPACE \f - FORMFEED \n - LINEFEED \r - RETURN \t - TAB \v - VERTICAL TAB Most of the other characters I tried, '\g', '\s', etc. just evaluate to the 2-character string of a backslash and the given character. I understand this is intentional, and makes sense to me. But '\x' is a problem. When my script reaches this source line: val = "\x" I get: ValueError: invalid \x escape What is so special about '\x'? Why is it treated differently from the other non-escaped characters?

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• Why maven is not working in eclipse indigo?

  - by user1067665

  I'm trying to make a simple log in/ log out web application with maven and I'm creating the project with the command: " mvn archetype:generate " and choose 341 and it'll be created with the structure below: webapp -----src/main/java -----Referenced Libraries -----Maven Dependencies -----src -----target pom.xml But when I add some dependencies and update the project something weird happening with the structure of the project according to the picture below: webapp -----src/main/java -----Referenced Libraries -----JRE System Library -----src -----target pom.xml and it's not working any more. As you can see the the first one has a Maven dependencies Library but the second one has been changed to JRE System Library. I use mac os lion and eclipse indigo. Anyone how knows why is like that? Tancks

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• WHY HAVE YOU ROMOVED MY POST? [closed]

  - by Eddy Freeman

  I posted a question about how to rotate a tile in BufferedImage. I did it in the morning and you removed it. Why have you removed it again? What is wrong with the posts? Tell me before i become angry. You have removed the post twice without informing/telling me the problem. with the posts What is wrong? Tell me. Reply to this post and tell me what is wrong.

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• Why this function overloading is not working?

  - by Jack

  class CConfFile { public: CConfFile(const std::string &FileName); ~CConfFile(); ... std::string GetString(const std::string &Section, const std::string &Key); void GetString(const std::string &Section, const std::string &Key, char *Buffer, unsigned int BufferSize); ... } string CConfFile::GetString(const string &Section, const string &Key) { return GetKeyValue(Section, Key); } void GetString(const string &Section, const string &Key, char *Buffer, unsigned int BufferSize) { string Str = GetString(Section, Key); // *** ERROR *** strncpy(Buffer, Str.c_str(), Str.size()); } Why do I get an error too few arguments to function ‘void GetString(const std::string&, const std::string&, char*, unsigned int)' at the second function ? Thanks

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• Global JavaScript Variable Scope: Why doesn't this work?

  - by CoryDorning

  So I'm playing around with JavaScript and came across what I think to be an oddity. Is anyone able to explain the following? (i've included the alerted values as comments) Why is the first alert(msg) inside foo() returning undefined and not outside? var msg = 'outside'; function foo() { alert(msg); // undefined var msg = 'inside'; alert(msg); // inside } foo(); alert(msg); // outside Considering these both work fine: var msg = 'outside'; function foo() { alert(msg); // outside } alert(msg); // outside and: var msg = 'outside'; function foo() { var msg = 'inside'; alert(msg); // inside } alert(msg); // outside

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• Setting enum values to 4-byte strings - why?

  - by psychotik

  I saw code similar to this in the Mac OS SDK: enum { kAudioFileStreamProperty_ReadyToProducePackets = 'redy', kAudioFileStreamProperty_FileFormat = 'ffmt', kAudioFileStreamProperty_DataFormat = 'dfmt', kAudioFileStreamProperty_FormatList = 'flst', kAudioFileStreamProperty_MagicCookieData = 'mgic', kAudioFileStreamProperty_AudioDataByteCount = 'bcnt', kAudioFileStreamProperty_AudioDataPacketCount = 'pcnt', kAudioFileStreamProperty_MaximumPacketSize = 'psze', kAudioFileStreamProperty_DataOffset = 'doff', kAudioFileStreamProperty_ChannelLayout = 'cmap', kAudioFileStreamProperty_PacketToFrame = 'pkfr', kAudioFileStreamProperty_FrameToPacket = 'frpk', kAudioFileStreamProperty_PacketToByte = 'pkby', kAudioFileStreamProperty_ByteToPacket = 'bypk', kAudioFileStreamProperty_PacketTableInfo = 'pnfo', kAudioFileStreamProperty_PacketSizeUpperBound = 'pkub', kAudioFileStreamProperty_AverageBytesPerPacket = 'abpp', kAudioFileStreamProperty_BitRate = 'brat' }; It's the first time I've seen this - I assume the compiler assigns the 32-bit integer equivalent of the strings to the enum values. I cannot think of a single good reason why this might be preferred over using simple integers. It looks hideous in a debugger (how do you tell which of these values corresponds to 1919247481?) and makes debugging just hard in general. So, is there any reason where assigning such strings to enum values actually makes sense.

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• why C clock() returns 0

  - by eddy ed

  I've got something like this: clock_t start, end; start=clock(); something_else(); end=clock(); printf("\nClock cycles are: %d - %d\n",start,end); and I always get as an output "Clock cycles are: 0 - 0" Any idea why this happens? (Just to give little detail, the something_else() function performs a left-to-right exponentiation using montgomery represantation, moreover I don't know for certain that the something_else() function does indeed take some not negligible time.) This is on Linux. The result of uname -a is: Linux snowy.*****.ac.uk 2.6.32-71.el6.x86_64 #1 SMP Fri May 20 03:51:51 BST 2011 x86_64 x86_64 x86_64 GNU/Linux

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• Why does coffeescript generate classes like this?

  - by ryeguy

  Given the following coffeescript code: class Animal constructor: (@name) -> speak: (things) -> "My name is #{@name} and I like #{things}" This is generated: var Animal = (function() { function Animal(name) { this.name = name; } Animal.prototype.speak = function(things) { return "My name is " + this.name + " and I like " + things; }; return Animal; })(); But why isn't this more idiomatic code generated? var Animal = function Animal(name) { this.name = name; }; Animal.prototype.speak = function(things) { return "My name is " + this.name + " and I like " + things; }; I know that coffeescript wraps a lot of stuff in anonymous functions to control scope leak, but what could leak here?

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• why does calling methods on a div fire the live click event

  - by oo

  i have this jquery code: $(this).parent('.copyFoodInstance').attr("myset", "0"); $(this).parent('.copyFoodInstance').html("<img BORDER=0 src='../../images/copy1.png' />"); it seems that when i call this code, this event fires: $(document).ready(function() { $('div.copyFoodInstance').live('click', function() { does anyone know why this event fires from the lines above? is there anyway to stop if from firing? All i am doing is updating an attribute on the div and updating the html. this shouldn't fire a click event?

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