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• If url exists Objective-c

  - by HiGuy Smith

  Hey, I have a program that needs to tell if an online image exists, but the only way that I've gotten this to work is by loading the image in a NSData pointer and checking if the pointer exists. - (BOOL)exists { NSString *filePath = @"http://couleeapps.hostei.com/BottomBox.png"; NSURL *url = [NSURL URLWithString:filePath]; NSData *imageData = [NSData dataWithContentsOfURL:url]; if (imageData) { return YES; } return NO; } This has worked for me, but my problem is that I have a very slow connection, and it takes forever to download the image. So my question is: is there a way to check if a image (say "http://couleeapps.hostei.com/BottomBox.png") is available without having to download it? Help is much appreciated HiGuy

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• A function's static and dynamic parent

  - by legends2k

  I'm reading Thinking in C++ (vol. 2): Whenever a function is called, information about that function is pushed onto the runtime stack in an activation record instance (ARI), also called a stack frame. A typical stack frame contains (1) the address of the calling function (so execution can return to it), (2) a pointer to the ARI of the function’s static parent (the scope that lexically contains the called function, so variables global to the function can be accessed), and (3) a pointer to the function that called it (its dynamic parent). The path that logically results from repetitively following the dynamic parent links is the dynamic chain, or call chain I'm unable to comprehend what the author means as function's static and dynamic parent. Also am not able to differentiate between item 1, 2 or 3. They all seem to be the same. Can someone please explain this passage to me?

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• Stack / base pointers in assembly

  - by flyingcrab

  I know this topic has been covered ad-naseum here, and other places on the internet - but hopefully the question is a simple one as I try to get my head around assembly... So if i understand correctly the ebp (base pointer) will point to the top of the stack, and the esp (stack pointer) will point to the bottom -- since the stack grows downward. esp therefore points to the 'current location'. So on a function call, once you've saved the ebp on the stack you insert a new stack frame - for the function. So in the case of the image below, if you started from N-3 you would go to N-2 with a function call. But when you are at N-2 - is your ebp == 25 and the esp == 24 (at least initially, before any data is placed on the stack)? Is this correct or am I of on a tangent here? Thanks!

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• ungetc in Python

  - by Dragos Toader

  Some file read (readlines()) functions in Python copy the file contents to memory (as a list) I need to process a file that's too large to be copied in memory and as such need to use a file pointer (to access the file one byte at a time) -- as in C getc(). The additional requirement I have is that I'd like to rewind the file pointer to previous bytes like in C ungetc(). Is there a way to do this in Python? Also, in Python, I can read one line at a time with readline() Is there a way to read the previous line going backward?

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• PyOpenGL: glVertexPointer() offset problem

  - by SurvivalMachine

  My vertices are interleaved in a numpy array (dtype = float32) like this: ... tu, tv, nx, ny, nz, vx, vy, vz, ... When rendering, I'm calling gl*Pointer() like this (I have enabled the arrays before): stride = (2 + 3 + 3) * 4 glTexCoordPointer( 2, GL_FLOAT, stride, self.vertArray ) glNormalPointer( GL_FLOAT, stride, self.vertArray + 2 ) glVertexPointer( 3, GL_FLOAT, stride, self.vertArray + 5 ) glDrawElements( GL_TRIANGLES, len( self.indices ), GL_UNSIGNED_SHORT, self.indices ) The result is that nothing renders. However, if I organize my array so that the vertex position is the first element ( ... vx, vy, vz, tu, tv, nx, ny, nz, ... ) I get correct positions for vertices while rendering but texture coords and normals aren't rendered correctly. This leads me to believe that I'm not setting the pointer offset right. How should I set it? I'm using almost the exact same code in my other app in C++ and it works.

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• GWT PagingScrollTable ( set a style on a particular cell of the header table )

  - by Mario

  I have a column Definition for each colume that extends AbstractColumnDefinition these columns are put in a DefaultTableDefinition PART OF a PagingScrollTable example: NAME | SIZE | RES | DELETE | this style (AT THE END OF THE PAGE ) is added to the column names if you notice all of them are with a cursor pointer , meaning a hand shows up when i hover above each one. I want to remove the cursor for some cells in the header like delete. HOW DO YOU set/add/remove a style on a particular cell of the header table of a PagingScrollTable? THANK YOU .gwt-ScrollTable .headerTable td { border-left: 1px solid #CCCCCC; border-right: 1px solid #CCCCCC; border-bottom: 1px solid black; vertical-align: bottom; cursor: pointer; }

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• Why does one loop take longer to detect a shared memory update than another loop?

  - by Joseph Garvin

  I've written a 'server' program that writes to shared memory, and a client program that reads from the memory. The server has different 'channels' that it can be writing to, which are just different linked lists that it's appending items too. The client is interested in some of the linked lists, and wants to read every node that's added to those lists as it comes in, with the minimum latency possible. I have 2 approaches for the client: For each linked list, the client keeps a 'bookmark' pointer to keep its place within the linked list. It round robins the linked lists, iterating through all of them over and over (it loops forever), moving each bookmark one node forward each time if it can. Whether it can is determined by the value of a 'next' member of the node. If it's non-null, then jumping to the next node is safe (the server switches it from null to non-null atomically). This approach works OK, but if there are a lot of lists to iterate over, and only a few of them are receiving updates, the latency gets bad. The server gives each list a unique ID. Each time the server appends an item to a list, it also appends the ID number of the list to a master 'update list'. The client only keeps one bookmark, a bookmark into the update list. It endlessly checks if the bookmark's next pointer is non-null ( while(node->next_ == NULL) {} ), if so moves ahead, reads the ID given, and then processes the new node on the linked list that has that ID. This, in theory, should handle large numbers of lists much better, because the client doesn't have to iterate over all of them each time. When I benchmarked the latency of both approaches (using gettimeofday), to my surprise #2 was terrible. The first approach, for a small number of linked lists, would often be under 20us of latency. The second approach would have small spats of low latencies but often be between 4,000-7,000us! Through inserting gettimeofday's here and there, I've determined that all of the added latency in approach #2 is spent in the loop repeatedly checking if the next pointer is non-null. This is puzzling to me; it's as if the change in one process is taking longer to 'publish' to the second process with the second approach. I assume there's some sort of cache interaction going on I don't understand. What's going on?

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• classes and static variables in shared libraries

  - by abel

  I am trying to write something in c++ with an architecture like: App -- Core (.so) <-- Plugins (.so's) for linux, mac and windows. The Core is implicitly linked to App and Plugins are explicitly linked with dlopen/LoadLibrary to App. The problem I have: static variables in Core are duplicated at run-time -- Plugins and App have different copys of them. at least on mac, when a Plugin returns a pointer to App, dynamic casting that pointer in App always result in NULL. Can anyone give me some explanations and instructions for different platforms please? I know this may seem lazy to ask them all here but I really cannot find a systematic answer to this question.

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• Objective-C getter/ setter question

  - by pic-o-matic

  Hi, im trying to works my way trough an Objective-C tutorial. In the book there is this example: @interface { int width; int height; XYPoint *origin; } @property int width, height; I though, hey there's no getter/setter for the XYPoint object. The code does work though. Now i'm going maybe to answer my own question :). I thinks its because "origin" is a pointer already, and whats happening under the hood with "width" and "height", is that there is going te be created a pointer to them.. Am i right, or am i talking BS :) ??

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• Any Win32 APIs to get the screenshots?

  - by Microkernel

  Hi all, I am writing an app, which needs to take the screen shots automatically (just like pressing PrintScreen button). So please suggest me how to get this done. A raw 24 bit BMP image would suffice. PLEASE NOTE: My app is in C, so any win32 APIs that can be called from my code is what I am looking for. (Sometimes back I had got an example code from codeproject which used to get the screen shots but the mouse pointer user to blink when the screen shot is taken. As multiple shots are taken this looks irritating to the user, so I don't want the mouse pointer to blink!) Regards, Chethan KR

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• Memory cleanup on returned array from static method (objective-c)

  - by Michael Bordelon

  In objective-c, I have a utility class with a bunch of static methods that I call for various tasks. As an example, I have one method that returns an NSArray that I allocate in the static method. If I set the NSArray to autorelease, then some time later, the NSArray in my calling method (that is assigned to the returned pointer) losses it's reference because the original form the static method is cleaned up. I can't release the NSArray object in the static method because it needs to be around for the return and assignment. What is the right way to return an object (like the NSArray) from a static class, and have it hang around for the calling class, but then get cleaned up later when it is no longer needed? Do I have to create the object first in the caller and pass in a pointer to the object and then return that same object form the static method? I know this is a basic O-O problem, I just never had this issue in Java and I do not do much C/C++. Thanks for your help.

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• How to achieve Bing maps like InfoWindow in Google Maps?

  - by BillB

  I'm using Google Maps v3. I really like the InfoWindows found in Bing, as opposed to Google. Screenshots & functionality found here comparing the two: http://www.axismaps.com/blog/2009/07/data-probing-and-info-window-design-on-web-based-maps/ Question: How can I replicate Bing like InfoWindows while using Google Maps v3? UPDATE: To be more specific, what I like about Bing's InfoWindows include: - The pointer dynamically changes sides from left/right/bottom/top, as opposed to Google limited to only have the InfoWindow pointer on the bottom - Bing's InfoWindows use less space - You can configure Bing's InfoWindows to pop up outside of the map bounders so that you don't have to autopan the map to display the marker's InfoWindow

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• Smart pointers and polymorphism

  - by qwerty

  hello. I implemented reference counting pointers (called SP in the example) and im having problems with polymorphism which i think i shouldn't have. In the following code: SP<BaseClass> foo() { // Some logic... SP<DerivedClass> retPtr = new DerivedClass(); return retPtr; } DerivedClass inherits from BaseClass. With normal pointers this should have worked, but with the smart pointers it says "cannot convert from 'SP<T>' to 'const SP<T>&" and i think it refers to the copy constructor of the smart pointer. How to i allow this kind of polymorphism with reference counting pointer? I'd appreciate code samples cause obviously im doing something wrong here if im having this problem. Thanks! :) [p.s., plz don't tell me to use standart liberary with smart pointers cuz that's impossible at this moment.]

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• ASP.NET MVC and ApplicationPath

  - by user93422

  Question is about paths and domains: I have an out-of-the box ASP.NET MVC project (generated by "File-New Project"). On LogOn page it does: return Redirect("~/Account/LogOn");. I have a domain name: mycompany.com, and following file structure on the server: /Root /MyApp (this is where my app goes into) Default.aspx ... I have set up following domain pointer: mycompany.com -> \MyApp When I go to mycompany.com I get an error, something about can't find mycompany.com/MyApp/MyApp/Account/LogOn Question: Where does second /MyApp path element comes from? Note: If I don't use domain pointer and deploy the site to the root - everything works just fine. Note: My hosting provider is webhost4life.com.

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• How do I specify the block object / predicate required by NSDictionary's keysOfEntriesPassingTest ?

  - by Todd

  For learning (not practical -- yet) purposes, I'd like to use the following method on an NSDictionary to give me back a set of keys that have values using a test I've defined. Unfortunately have no idea how to specify the predicate. NSDictionary keysOfEntriesPassingTest: - (NSSet *)keysOfEntriesPassingTest:(BOOL (^)(id key, id obj, BOOL *stop))predicate Let's say for example all my values are NSURLs, and I'd like to get back all the URLs that are on port 8080. Here's my stab at coding that -- though it doesn't really make sense to me that it'd be correct: NSSet * mySet = [myDict keysOfEntriesPassingTest:^(id key, id obj, BOOL *stop) { if( [[obj port] isEqual: [NSNumber numberWithInt: 8080]]) { return key; }] And that's because I get back the following compiler error: incompatible block pointer types initializing 'void (^)(struct objc_object *, struct objc_object *, BOOL *)', expected 'BOOL (^)(struct objc_object *, struct objc_object *, BOOL *)' What am I missing? I'd appreciate a pointer at some docs that go into more detail about the "Block object" that the predicate is supposed to be. Thanks!

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• Objective-C : Member variable is losing reference between method calls.

  - by Winston

  Hello, I've been having with an objective-c class which appears to be losing its pointer reference between methods of the same class. In the MyTableViewController.h file, I declare: @interface SettingsTableViewController : UITableViewController <UITextFieldDelegate>{ OCRAppDelegate *delegate; } MyTableViewController.m file - (id) init { self = [ super initWithStyle: UITableViewStyleGrouped ]; delegate = [(OCRAppDelegate *)[[UIApplication sharedApplication] delegate] retain]; } The problem is when the "MyTableViewController" view appears again and a different method is executed within that same class, the delegate pointer (which was assigned during the init method) is no longer there. I tried to retain, but to no avail. Would anyone know why this is, it seems like perhaps it is a fundamental Objective-C issue which I am missing. Appreciate your help. Thanks, Winston

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• May volatile be in user defined types to help writing thread-safe code

  - by David Rodríguez - dribeas

  I know, it has been made quite clear in a couple of questions/answers before, that volatile is related to the visible state of the c++ memory model and not to multithreading. On the other hand, this article by Alexandrescu uses the volatile keyword not as a runtime feature but rather as a compile time check to force the compiler into failing to accept code that could be not thread safe. In the article the keyword is used more like a required_thread_safety tag than the actual intended use of volatile. Is this (ab)use of volatile appropriate? What possible gotchas may be hidden in the approach? The first thing that comes to mind is added confusion: volatile is not related to thread safety, but by lack of a better tool I could accept it. Basic simplification of the article: If you declare a variable volatile, only volatile member methods can be called on it, so the compiler will block calling code to other methods. Declaring an std::vector instance as volatile will block all uses of the class. Adding a wrapper in the shape of a locking pointer that performs a const_cast to release the volatile requirement, any access through the locking pointer will be allowed. Stealing from the article: template <typename T> class LockingPtr { public: // Constructors/destructors LockingPtr(volatile T& obj, Mutex& mtx) : pObj_(const_cast<T*>(&obj)), pMtx_(&mtx) { mtx.Lock(); } ~LockingPtr() { pMtx_->Unlock(); } // Pointer behavior T& operator*() { return *pObj_; } T* operator->() { return pObj_; } private: T* pObj_; Mutex* pMtx_; LockingPtr(const LockingPtr&); LockingPtr& operator=(const LockingPtr&); }; class SyncBuf { public: void Thread1() { LockingPtr<BufT> lpBuf(buffer_, mtx_); BufT::iterator i = lpBuf->begin(); for (; i != lpBuf->end(); ++i) { // ... use *i ... } } void Thread2(); private: typedef vector<char> BufT; volatile BufT buffer_; Mutex mtx_; // controls access to buffer_ };

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• How does void QTableWidget::setItemPrototype ( const QTableWidgetItem * item ) clones objects?

  - by chappar

  QTableWidget::setItemPrototype says following. "The table widget will use the item prototype clone function when it needs to create a new table item. For example when the user is editing in an empty cell. This is useful when you have a QTableWidgetItem subclass and want to make sure that QTableWidget creates instances of your subclass." How does this actually work as you can pass any of the QTableWidgetItem subclass pointer to setItemPrototype and at run time there is no way you can get the size of an object having just pointer to it?

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• Exception_Record in python2.5 problem

  - by amir

  I'm using Python2.5 & the following code produce 2 errors. Can any body help me? class EXCEPTION_RECORD(Structure): _fields_ = [ ("ExceptionCode", DWORD), ("ExceptionFlags", DWORD), ("ExceptionRecord", POINTER(EXCEPTION_RECORD)), ("ExceptionAddress", LPVOID), ("NumberParameters", DWORD), ("ExceptionInformation", ULONG_PTR * EXCEPTION_MAXIMUM_PARAMETERS)] Python Error: Traceback (most recent call last): File "E:\Python25\my_debugger_defines.py", line 70, in <module> class EXCEPTION_RECORD(Structure): File "E:\Python25\my_debugger_defines.py", line 74, in EXCEPTION_RECORD ("ExceptionRecord", POINTER(EXCEPTION_RECORD)), NameError: name 'EXCEPTION_RECORD' is not defined Microsoft Document: The EXCEPTION_RECORD structure describes an exception. typedef struct _EXCEPTION_RECORD { // exr DWORD ExceptionCode; DWORD ExceptionFlags; struct _EXCEPTION_RECORD *ExceptionRecord; PVOID ExceptionAddress; DWORD NumberParameters; DWORD ExceptionInformation[EXCEPTION_MAXIMUM_PARAMETERS]; } EXCEPTION_RECORD; Thanks in advance

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• While loop in IL - why stloc.0 and ldloc.0?

  - by Michael Stum

  I'm trying to understand how a while loop looks in IL. I have written this C# function: static void Brackets() { while (memory[pointer] > 0) { // Snipped body of the while loop, as it's not important } } The IL looks like this: .method private hidebysig static void Brackets() cil managed { // Code size 37 (0x25) .maxstack 2 .locals init ([0] bool CS$4$0000) IL_0000: nop IL_0001: br.s IL_0012 IL_0003: nop // Snipped body of the while loop, as it's not important IL_0011: nop IL_0012: ldsfld uint8[] BFHelloWorldCSharp.Program::memory IL_0017: ldsfld int16 BFHelloWorldCSharp.Program::pointer IL_001c: ldelem.u1 IL_001d: ldc.i4.0 IL_001e: cgt IL_0020: stloc.0 IL_0021: ldloc.0 IL_0022: brtrue.s IL_0003 IL_0024: ret } // end of method Program::Brackets For the most part this is really simple, except for the part after cgt. What I don't understand is the local [0] and the stloc.0/ldloc.0. As far as I see it, cgt pushes the result to the stack, stloc.0 gets the result from the stack into the local variable, ldloc.0 pushes the result to the stack again and brtrue.s reads from the stack. What is the purpose of doing this? Couldn't this be shortened to just cgt followed by brtrue.s?

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• VIrtual class problem

  - by ugur

  What i think about virtual class is, if a derived class has a public base, let's say, class base, then a pointer to derived can be assigned to a variable of type pointer to base without use of any explicit type conversion. But what if, we are inside of base class then how can we call derived class's functions. I will give an example: class Graph{ public: Graph(string); virtual bool addEdge(string,string); } class Direct:public Graph{ public: Direct(string); bool addEdge(string,string); } Direct::Direct(string filename):Graph(filename){}; When i call constructor of Direct class then it calls Graph. Now lets think Graph function calls addedge. Graph(string str){ addedge(str,str); } When it calls addedge, even if the function is virtual, it calls Graph::edge. What i want is, to call Direct::addedge. How can it be done?

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• Virtual class problem

  - by ugur

  What i think about virtual class is, if a derived class has a public base, let's say, class base, then a pointer to derived can be assigned to a variable of type pointer to base without use of any explicit type conversion. But what if, we are inside of base class then how can we call derived class's functions. I will give an example: class Graph{ public: Graph(string); virtual bool addEdge(string,string); } class Direct:public Graph{ public: Direct(string); bool addEdge(string,string); } Direct::Direct(string filename):Graph(filename){}; When i call constructor of Direct class then it calls Graph. Now lets think Graph function calls addedge. Graph(string str){ addedge(str,str); } When it calls addedge, even if the function is virtual, it calls Graph::edge. What i want is, to call Direct::addedge. How can it be done?

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• 'whatever' has no declared type

  - by mihirpmehta

  i am developing parser using bison...in my grammar i am getting this error Here is a code extern NodePtr CreateNode(NodeType, ...); extern NodePtr ReplaceNode(NodeType, NodePtr); extern NodePtr MergeSubTrees(NodeType, ...); ................... NodePtr rootNodePtr = NULL; /* pointer to the root of the parse tree */ NodePtr nodePtr = NULL; /* pointer to an error node */ ........................... NodePtr mainMethodDecNodePtr = NULL; ................ /* YYSTYPE */ %union { NodePtr nodePtr; } i am getting this error whenever i use like $$.nodePtr or $1.nodePtr ... I am getting Parser.y:1302.32-33: $1 of `Expressi on' has no declared type

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• Objective-C member variable assignment?

  - by Alex

  I have an objective-c class with member variables. I am creating getters and setters for each one. Mostly for learning purposes. My setter looks like the following: - (void) setSomething:(NSString *)input { something = input; } However, in C++ and other languages I have worked with in the past, you can reference the member variable by using the this pointer like this->something = input. In objective-c this is known as self. So I was wondering if something like that is possible in objective-c? Something like this: - (void) setSomething:(NSString *)input { [self something] = input; } But that would call the getter for something. So I'm not sure. So my question is: Is there a way I can do assignment utilizing the self pointer? If so, how? Is this good practice or is it evil? Thanks!

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• How to create a container that holds different types of function pointers in C++?

  - by Alex

  I'm doing a linear genetic programming project, where programs are bred and evolved by means of natural evolution mechanisms. Their "DNA" is basically a container (I've used arrays and vectors successfully) which contain function pointers to a set of functions available. Now, for simple problems, such as mathematical problems, I could use one type-defined function pointer which could point to functions that all return a double and all take as parameters two doubles. Unfortunately this is not very practical. I need to be able to have a container which can have different sorts of function pointers, say a function pointer to a function which takes no arguments, or a function which takes one argument, or a function which returns something, etc (you get the idea)... Is there any way to do this using any kind of container ? Could I do that using a container which contains polymorphic classes, which in their turn have various kinds of function pointers? I hope someone can direct me towards a solution because redesigning everything I've done so far is going to be painful.

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