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• performSelector:withObject:afterDelay: not working from scrollViewDidZoom

  - by oldbeamer

  Hi all, I feel like I should know this but I've been stumped for hours now and I've run out of ideas. The theory is simple, the user manipulates the zoom and positioning in a scrollview using a pinch. If they hold that pinch for a short period of time then the scrollview records the zoom level and content offsets. So I thought I'd start a performSelector:withObject:withDelay on the scrollViewDidZoom delegate method. If it expires then I record the settings. I delete the scheduled call every time scrollViewDidZoom is called and when the pinch gesture finishes. This is what I have: - (void)scrollViewDidZoom:(UIScrollView *)scrollView{ NSLog(@"resetting timer"); [NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(positionLock) object:nil]; [self performSelector:@selector(positionLock) withObject:nil afterDelay:0.4]; } -(void)positionLock{ NSLog(@"position locked "); } - (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(float)scale{ NSLog(@"deleting timer"); [NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(positionLock) object:nil]; } This is the output: 2010-05-19 22:43:01.931 resetting timer 2010-05-19 22:43:01.964 resetting timer 2010-05-19 22:43:02.231 resetting timer 2010-05-19 22:43:02.253 resetting timer 2010-05-19 22:43:02.269 resetting timer 2010-05-19 22:43:02.298 resetting timer 2010-05-19 22:43:05.399 deleting timer As you can see the delay between the last and second last events should have been more than enough for the delayed selector call to execute. If I replace performSelector:withObject:withDelay with plain old performSelector: I get this: 2010-05-19 23:08:30.333 resetting timer 2010-05-19 23:08:30.333 position locked 2010-05-19 23:08:30.366 resetting timer 2010-05-19 23:08:30.367 position locked 2010-05-19 23:08:30.688 deleting timer Which isn't what I want but serves to show that it's only the delay that's causing it to not function, not something to do with the selector not being declared in the header, being misspelt or any other reason. Any ideas as to why it's not working?

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• About enumerations in Delphi and c++ in 64-bit environments

  - by sum1stolemyname

  I recently had to work around the different default sizes used for enumerations in Delphi and c++ since i have to use a c++ dll from a delphi application. On function call returns an array of structs (or records in delphi), the first element of which is an enum. To make this work, I use packed records (or aligned(1)-structs). However, since delphi selects the size of an enum-variable dynamically by default and uses the smallest datatype possible (it was a byte in my case), but C++ uses an int for enums, my data was not interpreted correctly. Delphi offers a compiler switch to work around this, so the declaration of the enum becomes {$Z4} TTypeofLight = ( V3d_AMBIENT, V3d_DIRECTIONAL, V3d_POSITIONAL, V3d_SPOT ); {$Z1} My Questions are: What will become of my structs when they are compiled on/for a 64-bit environment? Does the default c++ integer grow to 8 Bytes? Are there other memory alignment / data type size modifications (other than pointers)?

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• ObjC internals. Why my duck typing attempt failed?

  - by Piotr Czapla

  I've tried to use id to create duck typing in objective-c. The concept looks fine in theory but failed in practice. I was unable to use any parameters in my methods. The methods were called but parameters were wrong. I was getting BAD_ACESS for objects and random values for primitives. I've attached a simple example below. The question: Does any one knows why the methods parameters are wrong? What is happening under the hood of the objective-c? Note: I'm interest in the details. I know how to make the example below work. An example: I've created a simple class Test that is passed to an other class using property id test. @implementation Test - (void) aSampleMethodWithFloat:(float) f andInt: (int) i { NSLog(@"Parameters: %f, %i\n", f, i); } @end Then in the class the following loop is executed: for (float f=0.0f; f < 100.0f ; f += 0.3f) { [self.test aSampleMethodWithOneFloatParameter: f]; // warning: no method found. } Here is the output that I'm getting. As you can see the method was called but the parameters were wrong. Parameters: 0.000000, 0 Parameters: -0.000000, 1069128089 Parameters: -0.000000, 1070176665 Parameters: 2.000000, 1070805811 Parameters: -0.000000, 1071225241 Parameters: 0.000000, 1071644672 Parameters: 2.000000, 1071854387 Parameters: 36893488147419103232.000000, 1072064102 Parameters: -0.000000, 1072273817 Parameters: -36893488147419103232.000000, 1072483532

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• Opening Large (24 GB) File In C

  - by zacaj

  I'm trying to read in a 24 GB XML file in C, but it won't work. I'm printing out the current position using ftell() as I read it in, but once it gets to a big enough number, it goes back to a small number and starts over, never even getting 20% through the file. I assume this is a problem with the range of the variable that's used to store the position (long), which can go up to about 4,000,000,000 according to http://msdn.microsoft.com/en-us/library/s3f49ktz%28VS.80%29.aspx, while my file is 25,000,000,000 bytes in size. A long long should work, but how would I change what my compiler(Cygwin/mingw32) uses or get it to have fopen64?

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• Extract Generic types from extended Generic

  - by Brigham

  I'm trying to refactor a class and set of subclasses where the M type does extend anything, even though we know it has to be a subclass of a certain type. That type is parametrized and I would like its parametrized types to be available to subclasses that already have values for M. Is there any way to define this class without having to include the redundant K and V generic types in the parameter list. I'd like to be able to have the compiler infer them from whatever M is mapped to by subclasses. public abstract class NewParametrized<K, V, M extends SomeParametrized<K, V>> { public void someMethodThatTakesKAndV(K k1, V v1) { } } In other words, I'd like the class declaration to look something like: public class NewParametrized<M extends SomeParametrized<K, V>> { And K and V's types would be inferred from the definition of M.

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• Using sys/socket.h functions on windows

  - by BSchlinker

  Hello, I'm attempting to utilize the socket.h functions within Windows. Essentially, I'm currently looking at the sample code at http://beej.us/guide/bgnet/output/html/multipage/clientserver.html#datagram. I understand that socket.h is a Unix function -- is there anyway I can easily emulate that environment while compiling this sample code? Does a different IDE / compiler change anything? Otherwise, I imagine that I need to utilize a virtualized Linux environment, which may be best anyways as the code will most likely be running in a UNIX environment. Thanks.

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• c++ Using const in a copy constructor?

  - by Anton

  I have never written copy constructor, so in order to avoid pain i wanted to know if what i have coded is legit. It compiles but i am not sure that it works as a copy constructor should. Also do i have to use const in the copy constructor or i can simply drop it. (What i dont like about const is that the compiler cries if i use some non const functions). //EditNode.h class EditNode { explicit EditNode(QString elementName); EditNode(const EditNode &src); } //EditNodeContainer.h class EditNodeContainer : public EditNode { explicit EditNodeContainer(QString elementName); EditNodeContainer(const EditNodeContainer &src); } //EditNodeContainer.cpp EditNodeContainer::EditNodeContainer(QString elementName):EditNode(elementName) { } //This seems to compile but not sure if it works EditNodeContainer::EditNodeContainer(const EditNodeContainer &src):EditNode(src) { } //the idea whould be to do something like this EditNodeContainer *container1 = new EditNodeContainer("c1"); EditNodeContainer *copyContainer = new EditNodeContainer(container1);

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• 2-byte (UCS-2) wide strings under GCC

  - by Seva Alekseyev

  Hi all, when porting my Visual C++ project to GCC, I found out that the wchar_t datatype is 4-byte UTF-32 by default. I could override that with a compiler option, but then the whole wcs* (wcslen, wcscmp, etc.) part of RTL is rendered unusable, since it assumes 4-byte wide strings. For now, I've reimplemented 5-6 of these functions from scratch and #defined my implementations in. But is there a more elegant option - say, a build of GCC RTL with 2-byte wchar-t quietly sitting somewhere, waiting to be linked? The specific flavors of GCC I'm after are Xcode on Mac OS X, Cygwin, and the one that comes with Debian Linux Etch.

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• Error in my OO Generics design. How do I workaround it?

  - by John

  I get "E2511 Type parameter 'T' must be a class type" on the third class. type TSomeClass=class end; ParentParentClass<T>=class end; ParentClass<T: class> = class(ParentParentClass<T>) end; ChildClass<T: TSomeClass> = class(ParentClass<T>) end; I'm trying to write a lite Generic Array wrapper for any data type(ParentParentClass) ,but because I'm unable to free type idenitifiers( if T is TObject then Tobject(T).Free) , I created the second class, which is useful for class types, so I can free the objects. The third class is where I use my wrapper, but the compiler throws that error. How do I make it compile?

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• Are returned locals automatically xvalues

  - by mark

  Following on from a comment I made on this: passing std::vector to constructor and move semantics Is the std::move necessary in the following code, to ensure that the returned value is a xvalue? std::vector<string> buildVector() { std::vector<string> local; // .... build a vector return std::move(local); } It is my understanding that this is required. I have often seen this used when returning a std::unique_ptr from a function, however GManNickG made the following comment: It is my understanding that in a return statement all local variables are automatically xvalues (expiring values) and will be moved, but I'm unsure if that only applies to the returned object itself. So OP should go ahead and put that in there until I'm more confident it shouldn't have to be. :) Can anyone clarify if the std::move is necessary? Is the behaviour compiler dependent?

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• Custom class object in Initialization list

  - by Michael

  I have a class Bar: class Bar { public: Bar(void); ~Bar(void); }; And a class Foo that gets a reference to Bar object as a constructor parameter and needs to save it in a private member bar_ : class Foo { private: Bar& bar_; public: Foo(Bar& bar) : bar_(bar) {} ~Foo(void) {} }; This doesn't compile : overloaded member function not found in 'Parser' missing type specifier - int assumed. Note: C++ does not support default-int Now i suspect couple of things that i need to assure, the second error is for Bar& bar_; declaration in Foo. Do i need to use an explicit constructor when declaring bar_ ? I am interested in learning how the compiler works regarding this matter, so a detailed explanation would be highly appreciated. Thanks.

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• C# implicit conversions and == operator

  - by Arnis L.

  Some code for context: class a { } class b { public a a{get;set;} public static implicit operator a(b b) { return b.a; } } a a=null; b b=null; a = b; //compiler: cannot apply operator '==' to operands of type tralala... bool c = a == b; Is it possible to use == operator on different type instances, where one can implicitly convert to another? What did i miss? Edit: If types must be the same calling ==, then why int a=1; double b=1; bool c=a==b; works?

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• Why calling ISet<dynamic>.Contains() compiles, but throws an exception at runtime?

  - by Andrey Breslav

  Please, help me to explain the following behavior: dynamic d = 1; ISet<dynamic> s = new HashSet<dynamic>(); s.Contains(d); The code compiles with no errors/warnings, but at the last line I get the following exception: Unhandled Exception: Microsoft.CSharp.RuntimeBinder.RuntimeBinderException: 'System.Collections.Generic.ISet<object>' does not contain a definition for 'Contains' at CallSite.Target(Closure , CallSite , ISet`1 , Object ) at System.Dynamic.UpdateDelegates.UpdateAndExecuteVoid2[T0,T1](CallSite site, T0 arg0, T1 arg1) at FormulaToSimulation.Program.Main(String[] args) in As far as I can tell, this is related to dynamic overload resolution, but the strange things are (1) If the type of s is HashSet<dynamic>, no exception occurs. (2) If I use a non-generic interface with a method accepting a dynamic argument, no exception occurs. Thus, it looks like this problem is related particularly with generic interfaces, but I could not find out what exactly causes the problem. Is it a bug in the compiler/typesystem, or legitimate behavior?

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• Optional structural typing possibilty in C++ or anyother language?

  - by ambhai

  In C++ how to tell compiler that Ogre::Vector3 IS_SAME_AS SomeOtherLIB::Vector3 ? I feel that.. in languages like c++ which are not structural typed but there are cases when it makes sense. Normally as game developer when working with 4+ libraries that provide sort or their own Vector3 implementation. The code is littered with ToOgre, ToThis, ToThat conversion function. Thats a lot of Float3 copying around which should not happen on first place. Is in C++ or any other languages where we dont have to convert (copying) from one type to another which is essentially the samething. But any solution in C++ as most of the good gamedevs libs are for c/c++.

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• Problem with array of elements of a structure type

  - by kobac

  I'm writing an app in Visual Studio C++ and I have problem with assigning values to the elements of the array, which is array of elements of structure type. Compiler is reporting syntax error for the assigning part of the code. Is it possible in anyway to assign elements of array which are of structure type? typedef struct { CString x; double y; } Point; Point p[3]; p[0] = {"first", 10.0}; p[1] = {"second", 20.0}; p[2] = {"third", 30.0};

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• Force external function to be const

  - by vanna

  Here is my problem. I made a class with a member function declared as const that uses an external function that I cannot modify (declared in someone else's code) and that is not declared const. More precisely Someone else's code class B { public: void foo(); }; My code class A : public B { public: void bar() const { this->foo(); } }; I know that for member data we can force const-correctness by using mutable or const_cast. How can I 'hack' foo such that my compiler understands that I would like to use it as if it was const even if it is not declared in someone else's code ?

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• mmap only needed pages of kernel buffer to user space

  - by axeoth

  See also this answer: http://stackoverflow.com/a/10770582/1284631 I need something similar, but without having to allocate a buffer: the buffer is large, in theory, but the user space program only needs to access some parts of it (it mocks some registers of a hardware). As I cannot allocate with vmalloc_user() such a large buffer (kernel 32 bit, in embedded environment, no swap...), I followed the same approach as in the quoted answer, trying to allocate only those pages that are really requested by the user space. So: I use a my_mmap() function for the device file (actually, is the .mmap field of a struct uio_info) to set up the fields of the vma, then, in the vm_area_struct's .fault field (also named my_fault()), I should return a page. except that: In the my_fault() method of vm_area_struct, I cannot obtain a page through: vmf->page=vmalloc_to_page(my_buf + (vmf->pgoff << PAGE_SHIFT)); since there is no allocated buffer: my_buf = vmalloc_user(MY_BUF_SIZE); fails with "allocation failed: out of vmalloc space - use vmalloc= to increase size." (and there is no room or swap to increase that vmalloc= parameter). So, I would need to get a page from the kernel and fill the vmf->page field. How to allocate a page (I assume that the offset of the page is known, as it is vm->pgoff). What base memory should I use instead of my_buf? PS: I also did set up the vma->flags |= VM_NORESERVE; (in the my_mmap()), but not sure if it helps. Is there any vmalloc_user_unreserved()-like function? (let's say, lazy allocation) Also, writing 1 to /proc/sys/vm/overcommit_memory and large values (eg 500) to /proc/sys/vm/overcommit_ratio before trying to my_buf=vmalloc_user(<large_size>) didn't work.

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• Is it possible to use Dependency Injection/IoC on an ASP.NET MVC FilterAttribute ?

  - by Pure.Krome

  Hi folks, I've got a simple custom FilterAttribute which I use decorate various ActionMethods. eg. [AcceptVerbs(HttpVerbs.Get)] [MyCustomFilter] public ActionResult Bar(...) { ... } Now, I wish to add some logging to this CustomFilter Action .. so being a good boy, I'm using DI/IoC ... and as such wish to use this pattern for my custom FilterAttribute. So if i have the following... ILoggingService and wish to add this my custom FilterAttribute .. i'm not sure how. Like, it's easy for me to do the following... public class MyCustomFilterAttribute : FilterAttribute { public MyCustomFilterAttribute(ILoggingService loggingService) { ... } } But the compiler errors saying the attribute which decorates my ActionMethod (listed above...) requires 1 arg .. so i'm just not sure what to do :(

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• How does compilation work with AOP?

  - by alee

  I need quick answer to a simple thing in AOP. If i have a code deployed at client side and i have written new aspects, which i want in the client side software. do i have to "recompile" complete software with "original" code and new "AOP" code? (with aop compiler)? i.e. do i need the source code of original program with source code of new AOP and compile 'em boht? P.S: I am asking in general, not being specific to any language.

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• C++ overloading virtual = operator

  - by taz

  Hello, here is the code for my question: class ICommon { public: virtual ICommon& operator=(const ICommon & p)const=0; }; class CSpecial : public ICommon { public: CSpecial& operator=(const CSpecial & cs) { //custom operations return *this; } }; CSpecial obj; Basically: I want the interface ICommon to force it's descendants to implement = operator but don't want to have any typecasts in the implementation. The compiler says "can't instantiate an abstract class. Any help/advice will be appreciated.

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• Should I bundle C libraries with my Python application?

  - by oceanhug

  If I have a Python package that depends on some C libraries (like say the Gnu Scientific Library (GSL) for numerical computations), is it a good idea to bundle the library with my code? I'd like to make my package as easy to install as possible for users and I don't want them to have to download C libraries by hand and supply include-paths. Also I could always ensure that the version of the library that I ship is compatible with my code. However, is it possible that there are clashes if the user has the library installed already, or ar there any other reasons why I shouldn't do this? I know that I can make it easier for users by just providing a binary distribution, but I'd like to avoid having to maintain binary distributions for all possible OSs. So, I'd like to stick to a source distribution, but for the user (who proudly owns a C compiler) installation should be as easy as python setup.py install.

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• File IO, Handling CRLF

  - by aCuria

  Hi, i am writing a program that takes a file and splits it up into multiple small files of a user specified size, then join the multiple small files back again. 1) the code must work for c, c++ 2) i am compiling with multiple compilers. I am reading and writing to the files by using the stl functions fread() and fwrite() The problem I am having pertains to CRLF. If the file I am reading from contains CRLF, then I want to retain it when i split and join the files back together. If the file contains LF, then i want to retain LF. Unfortunately, fread() seems to store CRLF as \n (I think), and whatever is written by fwrite() is compiler-dependent. How do i approach this problem? Thanks.

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• Using Qt with custom MinGW

  - by ereOn

  Hi, I don't know if this question would fit better on superuser.com, but since it's rather compiler related, I give it a try here. I have to use Qt with a specific version of gcc (4.5). I downloaded the last official Qt release for Windows (Vista, 32 bits version) and didn't install the shipped MinGW version; I just installed the Qt libraries/binaries. In a console, when I type qmake && make, make fails, complaining that 'g++' is not recognized as an internal command. If I type g++ in the same console, I however have the following output: g++: no input files So g++ is definitely recognized. For those who may ask, both the Qt binaries directory and MinGW binaries directory are in the system PATH environment variable. What could be wrong here ?

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• Using type hints in Clojure for Java return values

  - by mikera

  I'm working on some Java / Clojure interoperability and came across a reflection warning for the following code: (defn load-image [resource-name] (javax.imageio.ImageIO/read (.getResource (class javax.imageio.ImageIO) resource-name))) => Reflection warning, clojure/repl.clj:37 - reference to field read can't be resolved. I'm surprised at this because getResource always returns a URL and I would therefore expect the compiler to use the appropriate static method in javax.imageio.ImageIO/read. The code works fine BTW so it is clearly finding the right method at run time. So two questions: Why is this returning a reflection warning? What type hint do I need to fix this?

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• SQL Server INSERT, Scope_Identity() and physical writing to disc

  - by TheBlueSky

  Hello everyone, I have a stored procedure that does, among other stuff, some inserts in different table inside a loop. See the example below for clearer understanding: INSERT INTO T1 VALUES ('something') SET @MyID = Scope_Identity() ... some stuff go here INSERT INTO T2 VALUES (@MyID, 'something else') ... The rest of the procedure These two tables (T1 and T2) have an IDENTITY(1, 1) column in each one of them, let's call them ID1 and ID2; however, after running the procedure in our production database (very busy database) and having more than 6250 records in each table, I have noticed one incident where ID1 does not match ID2! Although normally for each record inserted in T1, there is record inserted in T2 and the identity column in both is incremented consistently. The "wrong" records were something like that: ID1 Col1 ---- --------- 4709 data-4709 4710 data-4710 ID2 ID1 Col1 ---- ---- --------- 4709 4710 data-4709 4710 4709 data-4710 Note the "inverted", ID1 in the second table. Knowing not that much about SQL Server underneath operations, I have put the following "theory", maybe someone can correct me on this. What I think is that because the loop is faster than physically writing to the table, and/or maybe some other thing delayed the writing process, the records were buffered. When it comes the time to write them, they were wrote in no particular order. Is that even possible if no, how to explain the above mentioned scenario? If yes, then I have another question to rise. What if the first insert (from the code above) got delayed? Doesn't that mean I won't get the correct IDENTITY to insert into the second table? If the answer of this is also yes, what can I do to insure the insertion in the two tables will happen in sequence with the correct IDENTITY? I appreciate any comment and information that help me understand this. Thanks in advance.

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