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• Which index is used in select and why?

  - by Lukasz Lysik

  I have the table with zip codes with following columns: id - PRIMARY KEY code - NONCLUSTERED INDEX city When I execute query SELECT TOP 10 * FROM ZIPCodes I get the results sorted by id column. But when I change the query to: SELECT TOP 10 id FROM ZIPCodes I get the results sorted by code column. Again, when I change the query to: SELECT TOP 10 code FROM ZIPCodes I get the results sorted by code column again. And finally when I change to: SELECT TOP 10 id,code FROM ZIPCodes I get the results sorted by id column. My question is in the title of the question. I know which indexes are used in the queries, but my question is, why those indexes are used? I the second query (SELECT TOP 10 id FROM ZIPCodes) wouldn't it be faster if the clusteder index was used? How the query engine chooses which index to use?

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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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• What is the best software to write and organize written copy / content for a website?

  - by johnqtaxpayer

  I'm a newbie product manager, looking for tips on how to write and organize text copy for my company's website. I need to be able to prepare the content for our public site and turn it over to the web designer who publishes it to our live site. I want our UI team to be able to quickly glance at the copy I write and immediately know where on the page I intend for it to go. Currently, I'm using microsoft word to write and color code different text to signify where I want specific text to go. It is difficult for the UI guy to immediately know if something goes into the nav bar or into a header or a description below a header. In addition to that, it would be helpful for me to be able to write the copy in such a way that the web designer could copy and paste it into the XHTML without having to go back and manually replace special punctuation characters with the XHTML entities. What software is out there that will allow a comprehensive solution to these web copywriting issues?

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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 does py2exe remove `help` and `license`?

  - by cool-RR

  I packaged my Python app with py2exe. My app is a wxPython GUI, in which there is an interactive Python shell. I noticed that I can't do help(whatever) in the shell. I investigated a bit and discovered that after the py2exe process, 3 items were missing from __builtin__. These are help, license, and another one I haven't discovered. Why is this happening and how can I stop it? I want the users of my program to be able to use the help function of Python.

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• Why Java cannot find my constructor?

  - by Roman

  Well, maybe it is a stupid question, but I cannot resolve this problem. In my ServiceBrowser class I have this line: ServiceResolver serviceResolver = new ServiceResolver(ifIndex, serviceName, regType, domain); And compiler complains about it. It says: cannot find symbol symbol : constructor ServiceResolver(int,java.lang.String,java.lang.String,java.lang.String) This is strange, because I do have a constructor in the ServiceResolver: public void ServiceResolver(int ifIndex, String serviceName, String regType, String domain) { this.ifIndex = ifIndex; this.serviceName = serviceName; this.regType = regType; this.domain = domain; } ADDED: I removed void from the constructor and it works! Why?

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• Why is const required [C++] ? [closed]

  - by Andy Leman

  Possible Duplicate: What's the difference between a const member function and a non-const member function? class Message { public: Message(const char* pStr, const char* key); Message(const char* pStr); Message(); void encryptMessage(); void decryptMessage(); const char* getUnMessage() const; const char* getEnMessage() const; void getMessage(); void getKey(); ~Message(); private: char* pUnMessage; char* pEnMessage; char* pKey; }; In this program, why using const? (2 different places) Please explain those 2 for me. Thank you very much!

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• why nResult != nConvertedLen,when use CComBSTR;

  - by hxboxy

  CComBSTR wsData = (char*)pvData; when constuct CComBSTR,call A2WBSTR,but sometimes nResult != nConvertedLen,just 1/20. why? inline BSTR A2WBSTR(_In_opt_ LPCSTR lp, int nLen = -1) { if (lp == NULL || nLen == 0) return NULL; USES_CONVERSION_EX; BSTR str = NULL; #pragma warning(push) #pragma warning(disable: 6385) int nConvertedLen = MultiByteToWideChar(_acp_ex, 0, lp, nLen, NULL, NULL); #pragma warning(pop) int nAllocLen = nConvertedLen; if (nLen == -1) nAllocLen -= 1; // Don't allocate terminating '\0' str = ::SysAllocStringLen(NULL, nAllocLen); if (str != NULL) { int nResult; nResult = MultiByteToWideChar(_acp_ex, 0, lp, nLen, str, nConvertedLen); ATLASSERT(nResult == nConvertedLen); if(nResult != nConvertedLen) { SysFreeString(str); return NULL; } } return str; }

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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 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 are my \n not working in PHP?

  - by Strawberry

  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 does this code crash?

  - by user146780

  The following code causes a stack overflow but I don't see why... int _tmain(int argc, _TCHAR* argv[]) { cout << "start"; char bmp[1024][768][3]; for (int p = 0; p < 9000; ++p) { for(int i = 0; i < 1024; ++i) { for(int j = 0; j < 768; ++j) { bmp[i][j][0] = 20; } } } cout << "Stop"; return 0; } Thanks

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• Why operator= returns reference not const reference

  - by outmind

  The original question is related to overloading operator= and I like to share my findings as it was nontrivial for me to find them. I cannot imagine reasonable example to use (a=b) as lvalue. With the help of IRC and google I've found the next article: http://msdn.microsoft.com/en-us/magazine/cc301415.aspx it provides two examples. (a=b)=c f(T& ); f(a=b) but both a bit not good, as first violate associativity and I believe that it is bad practice. The second one give me the same feeling. Could you provide more good examples why it should be non constant?

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• Why doesn't variable img increase?

  - by Annette B

  I can upload image but the sprite name remains pict1 each time I upload another image. Why doesn't imgVal function increase? function imgVal() { img += 1; trace("image: pict" + img); } imgVal(); _fla.lights_mc.visible=false; _fla.lights_mc.stop(); _fla.pre_mc.fill_mc.stop(); _fla.pre_mc.visible=false; var sprite:Sprite=new Sprite(); sprite.addChild(loader); sprite.name = "pict" + img; //trace(sprite.name); _fla.myBorder.box.addChild(sprite); I'd like each sprite to be given a new name like pict1, pict2, pict3, etc but img variable is not increasing. I think this is where my problem occurs. Would someone please help?

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• Why did this code still work?

  - by bstullkid

  Some old code that I just came across: MLIST * new_mlist_link() { MLIST *new_link = (MLIST * ) malloc(sizeof(MLIST)); new_link->next = NULL; new_link->mapi = NULL; new_link->result = 0; } This was being called to build a linked list, however I noticed there is no statement: return new_link; Even without the return statement there, the list still got built properly. Why did this happen? EDT: Platform: Mandriva 2009 64bit Linux 2.6.24.7-server GCC 4.2.3-6mnb1

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• Why doesn't my viewmodel properties get populated

  - by Jakob

  Hi. I've looked all over and I can't figure out why my viewmodel doesn't get populated. I have this code: Followers = new ObservableCollection<aspnet_User>(_followersRepo.aspnet_Users); _followersRepo.Load(_followersRepo.GetUsersFollowingIDQuery(CurrentUserId)); Following = new ObservableCollection<aspnet_User>(_followingRepo.aspnet_Users); _followingRepo.Load(_followingRepo.GetUsersFollowedByIDQuery(CurrentUserId)); CurrentUser = _fullUserRepo.FullUsers.SingleOrDefault(); _fullUserRepo.Load(_fullUserRepo.GetFullUserByIDQuery(CurrentUserId)); But when I debug, there is no data loaded to the Followers, Following and CurrentUser objects. I know that data should be returned because I'm trying to implement the MVVM pattern in my app, and haven't changed the domainservice. Also I can se debugging the CurrentUserId has a value.

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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 do we need a private constructor?

  - by isthatacode

  if a class has a private constructor then it cant be instantiated. so, if i dont want my class to be instantiated and still use it, then i can make it static. what is the use of a private constructor ? Also its used in singleton class, except that, is there any othe use ? (Note : The reason i am excuding the singleton case above is because I dont understand why do we need a singleton at all ? when there is a static class availble. You may not answer for my this confusion in the question. )

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• Where can I write a temp file from ASP.NET?

  - by ProfK

  I have an 'access denied' problem on an ASP.NET web application, where the user uploads an Excel file and I try and write it to a folder. I don't have access to the host except FTP, so I can't set permissions. I thought that ASP.NET would be able to write to a folder that is under the web app root, but it isn't so. Is there anywhere I can write the file to that doesn't require me to set permissions?

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• Why is false being returned in this function

  - by Kay

  Hello all, I have this function below which makes it to the second IF function which sets the variable th as true but what is returned is false? Why?! public boolean nodeExist(TreeNode Tree, T value){ boolean th = false; if(Tree.getValue()!= null){ if(value == Tree.getValue()){ th = true; }else{ if(value.compareTo((T) Tree.getValue()) < 0){ nodeExist(Tree.getLeft(), value); }else{ nodeExist(Tree.getRight(), value); } } }else{ th = false; } return th; }

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• Why I have to redeclare a virtual function while overriding [C++]

  - by Neeraj

  #include <iostream> using namespace std; class Duck { public: virtual void quack() = 0; }; class BigDuck : public Duck { public: // void quack(); (uncommenting will make it compile) }; void BigDuck::quack(){ cout << "BigDuckDuck::Quack\n"; } int main() { BigDuck b; Duck *d = &b; d->quack(); } Consider this code, the code doesn't compiles. However when I declare the virtual function in the subclass, then it compiles fine. The compiler already has the signature of the function which the subclass will override, then why a redeclaration is required? Any insights.

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• Why does my ConfirmButtonExtender cause full postbacks after I've toggled its parent usercontrol's v

  - by zk812

  Hello all, I have a series of usercontrols on a page that are displayed based on a selection. Each usercontrol contains a Delete button with a ConfirmButton/ModalPopupExtender combo attached to it. This works great when first loading any of the usercontrols--clicking delete shows my Confirm Modal popup and hitting yes or no causes an async postback to perform the operation. But if I move away from the usercontrol and come back to it, the Confirm Modal Popup appears but clicking yes or no now causes a full postback (the operation does still take place). Why does changing the visible property cause this?

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• why is this legal, c++ typedef func

  - by acidzombie24

  i did this in msvc 2005. typedef void (*cleanup_t)(); void func(cleanup_t clean) { cleanup_t(); } Why does this compile? and not give me a warning? ok, it gave me a unreferenced formal parameter warning but originally i did this when clean was in a class no there was no unreferenced formal parameter when this code gave me problems. What is cleanup_t(); really doing and what is the point? now for laughs i tried int() and that worked also.

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• Why doesn't list.get(0).equals(null) work?

  - by Jessy

  The first index is set to null (empty), but it doesn't print the right output, why? //set the first index as null and the rest as "High" String a []= {null,"High","High","High","High","High"}; //add array to arraylist ArrayList<Object> choice = new ArrayList<Object>(Arrays.asList(a)); for(int i=0; i<choice.size(); i++){ if(i==0){ if(choice.get(0).equals(null)) System.out.println("I am empty"); //it doesn't print this output } }

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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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