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• Strange behaviour of Android debugger in Eclipse when using Camera for preview.

  - by Buzzy

  Hi, I have an Android application that uses a SurfaceView subclass and Camera object to preview images before capture. Once I capture an image, I stop the preview and release the camera. Execution stops at any breakpoint after this. However, apart from the "Suspend" and "Terminate" icons, the rest are disabled. This is strange because the "Debug Current Instruction Pointer" is clearly at the said breakpoint and execution is already suspended. I can't perform any debugging operations and have no option but to terminate the session. Sometimes (very rarely), the session terminates by itself. I can confirm that this odd behavior takes place only after I preview the camera capture. I am fairly new to Android development. Is there some obvious mistake I am making? Any help would be highly appreciated.

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• How is inheritance implemented at the memory level?

  - by cambr

  Suppose I have class A { public: void print(){cout<<"A"; }}; class B: public A { public: void print(){cout<<"B"; }}; class C: public C { }; How is inheritance implemented at the memory level? Does C copy print() code to itself or does it have a pointer to the it that points somewhere in A part of the code? How does the same thing happen when we override the previous definition, for example in B (at the memory level)?

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• Distributing players to tables

  - by IVlad

  Consider N = 4k players, k tables and a number of clans such that each member can belong to one clan. A clan can contain at most k players. We want to organize 3 rounds of a game such that, for each table that seats exactly 4 players, no 2 players sitting there are part of the same clan, and, for the later rounds, no 2 players sitting there have sat at the same table before. All players play all rounds. How can we do this efficiently if N can be about ~80 large? I thought of this: for each table T: repeat until 4 players have been seated at T: pick a random player X that is not currently seated anywhere if X has not sat at the same table as anyone currently at T AND X is not from the same clan as anyone currently at T seat X at T break I am not sure if this will always finish or if it can get stuck even if there is a valid assignment. Even if this works, is there a better way to do it?

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• What is on the 68000 stack when classic MacOS enters a program?

  - by John Källén

  I'm trying to understand an old classic Mac application's entry point. I've disassembled the first CODE resource (not CODE#0, which is the jump table). The code refers to some variables off the stack: a word at 0004(A7), an array of long words of starting at 000C(A7) whose length is the value at 0004(A7), and a final long word beyond that array that seems to be a pointer to a character string. The array of long words looks like strings at first glance, so it looks superficially like we're dealing with an (int argc, char ** argv) situation, except the "argv" array is inline in the stack frame. What should a program be expecting on its stack / registers when it first gets called by the Mac OS?

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• g++ doesn't think I'm passing a reference

  - by Ben Jones

  When I call a method that takes a reference, g++ complains that I'm not passing a reference. I thought that the caller didn't have to do anything different for PBR. Here's the offending code: //method definition void addVertexInfo(VertexInfo &vi){vertexInstances.push_back(vi);} //method call: sharedVertices[index]->addVertexInfo(VertexInfo(n1index, n2index)); And here's the error: GLUtils/GLMesh.cpp: In member function 'void GLMesh::addPoly(GLIndexedPoly&)': GLUtils/GLMesh.cpp:110: error: no matching function for call to 'SharedVertexInfo::addVertexInfo(VertexInfo)' GLUtils/GLMesh.h:93: note: candidates are: void SharedVertexInfo::addVertexInfo(VertexInfo&)

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• Manage bad_alloc exception in C++ construtor

  - by Jimmy zhang

  I have Java experience and recently am doing some C++ coding. My question is that if I have class A, in which I have to instantiate class B and class C as two of the member variables of A. If in the constructor of A, should I assume that allocations of class B and C never fail, and handle the bad allocation exception in the destructor of A? If I don't make that assumption, meaning that I add some try catch block to catch bad_alloc of class B and class C, then if the allocation exception occurs, should I do clean up in the constructor of A? What are the recommended practices? If "new" generates a bad allocation, what value does the pointer carry?

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• boost.asio's socket's recieve/send functions are bad?

  - by the_drow

  Data may be read from or written to a connected TCP socket using the receive(), async_receive(), send() or async_send() member functions. However, as these could result in short writes or reads, an application will typically use the following operations instead: read(), async_read(), write() and async_write(). I don't really understand that remark as read(), async_read(), write() and async_write() can also end up in short writes or reads, right? Why are those functions not the same? Should I use them at all? Can someone clarify that remark for me?

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• C++ allocate objects on heap of base class with protected constructors via inheritance

  - by KRao

  I have a class with protected constructor: class B { protected: B(){}; }; Now I derive from it and define two static functions and I manage to actually create objects of the class B, but not on the heap: class A : public B { public: static B createOnStack() {return B();} //static B* createOnHeap() {return new B;} //Compile time Error on VS2010 }; B b = A::createOnStack(); //This works on VS2010! The question is: 1) Is VS2010 wrong in allowing the first case? 2) Is it possible to create objects of B without modifying B in any way (no friendship and no extra functions). I am asking, because it is possible to make something similar when dealing with instances of B and its member functions, see: http://accu.org/index.php/journals/296 Thank you in advance for any suggestion! Kind regards

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• Help with Magento and related products

  - by Anthony

  I have a customer product page that literally lives beside the catalog/product/view.phtml page. It's basically identical to that page with a few small exceptions. It's basically a 'product of the day' type page so I can't combine it with the regular product page since I have to fetch the data from the DB and perform a load to get the product information $_product = Mage::getModel('catalog/product')->load($row['productid']); To make a long story short, everything works (including all children html blocks) with the singular exception of the related products. After the load I save the product into the registry with Mage::register('product', $_product); and then attempt to load the related products with: echo $this->getLayout()->createBlock('catalog/product_view')->setTemplate('catalog/product/list/related.phtml')->toHtml();` All of which give back the error: Fatal error: Call to a member function getSize() on a non-object in catalog/product/list/related.phtml on line 29`, and line 29 is <?php if($this->getItems()->getSize()): ?>`. Any help getting the relateds to load would be appreicated.

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• ListView created programmatically - emptyView doesn't show

  - by Yorick

  I've created custom ListView programmatically, and set view to show when ListAdapter is empty but nothing shows on the screen in that case, what can be wrong? public PlayerList(Context context, Activity activity) { super(context); mParent = activity; setOnItemClickListener( new OnItemClickListener() { public void onItemClick(AdapterView<?> parent, View view, int position, long id) { ... } }; List<PlayerInfo> players; players = getPlayerList(); // here size of players == 0 setAdapter(new PlayersAdapter(this.getContext(), R.id.player_name, players)); LayoutInflater vi = (LayoutInflater)mParent.getSystemService(Context.LAYOUT_INFLATER_SERVICE); emptyView = vi.inflate(R.layout.empty_view, null); // emptyView is View, and member of PlayerList this.setEmptyView(emptyView); }

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• What elegant method callback design should be used ?

  - by ereOn

  Hi, I'm surprised this question wasn't asked before on SO (well, at least I couldn't find it). Have you ever designed a method-callback pattern (something like a "pointer" to a class method) in C++ and, if so, how did you do it ? I know a method is just a regular function with some hidden this parameter to serve as a context and I have a pretty simple design in mind. However, since things are often more complex than they seem to, I wonder how our C++ gurus would implement this, preferably in an elegant and standard way. All suggestions are welcome !

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• Compiling C++ when two classes references one another

  - by Omry

  I am trying to write a simple wrapper around a connection pointer that will return it to the pool when the wrapper is destroyed. but it wont compile because the ConnectionPool and AutoConn need each other to be declared. I tried to use forward deceleration but it didn't work. how do I solve this? (using g++) class Connection {}; class ConnectionPool { Connection *m_c; public: AutoConn getConn() { return AutoConn(this, m_c); // by value } void releaseConnection(Connection *c) { } }; class AutoConn { ConnectionPool* m_pool; Connection *m_connection; public: AutoConn(ConnectionPool* pool, Connection *c) : m_pool(pool), m_connection(c) {} ~AutoConn() { m_pool->releaseConnection(m_connection); } };

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• How to save/export a DOM element to an image?

  - by Don Don

  Hi, I have a web page which has a form element (with its ID known) and inside the form there are multiple DIVs, and the position of each div may be changed. What I'd like to do is: a) Save the current state of this form // var currentForm=document.forms['myFrm'].innerHTML; would probably suffice... b) Save or export the entire form with the most current position of each DIV to an image file. // how to save/export the javascript var of currentForm to an image file is the key question. Any help/pointer would be appreciated.

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• Barcode field length

  - by bestattendance

  I'm writing some attendance software. Each member will have an ID card with a barcode which they will use to sign in to events. How long should the barcode field be in my database? I'd like to accept Code 39 and Code 128 barcodes. I know these are variable length codes, so what should I set the max length to? Thanks! EDIT: My clients will be using a variety of third-party barcode printing tools.

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• How do I release an object allocated in a different AutoReleasePool ?

  - by ajcaruana

  Hi, I have a problem with the memory management in Objective-C. Say I have a method that allocates an object and stores the reference to this object as a member of the class. If I run through the same function a second time, I need to release this first object before creating a new one to replace it. Supposing that the first line of the function is: NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; This means that a different auto-release pool will be in place. The code to allocate the object is as follows: if (m_object != nil) [m_object release]; m_object = [[MyClass alloc] init]; [m_object retain]; The problem is that the program crashes when running the last line of the method: [pool release]; What am I doing wrong ? How can I fix this ? Regards Alan

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• What does "static" mean in the context of declaring global template functions?

  - by smf68

  I know what static means in the context of declaring global non-template functions (see e.g. What is a "static" function?), which is useful if you write a helper function in a header that is included from several different locations and want to avoid "duplicate definition" errors. So my question is: What does static mean in the context of declaring global template functions? Please note that I'm specifically asking about global, non-member template functions that do not belong to a class. In other words, what is the difference between the following two: template <typename T> void foo(T t) { /* implementation of foo here */ } template <typename T> static void bar(T t) { /* implementation of bar here */ }

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• C++'s unordered_map / hash_map / Google's dense_hash - how to input binary data (buf+len) and insert

  - by shlomif

  Hi all, I have two questions about Google's dense_hash_map, which can be used instead of the more standard unordered_map or hash_map: How do I use an arbitrary binary data memory segment as a key: I want a buffer+length pair, which may still contain some NUL (\0) characters. I can see how I use a NUL-terminated char * string , but that's not what I want. How do I implement an operation where I look if a key exists, and if not - insert it and if it does return the pointer to the existing key and let me know what actually happened. I'd appreciate it if anyone can shed any light on this subject. Regards, -- Shlomi Fish

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• Swap byte 2 and 4 from integer

  - by czar x

  I had this interview question - Swap byte 2 and byte4 within an integer sequence. Integer is a 4byte wide i.e. 32 bits My approach was to use char *pointer and a temp char to swap the bytes. For clarity i have broken the steps otherwise an character array can be considered. unsigned char *b2, *b4, tmpc; int n = 0xABCD; b2 = &n; b2++; b4 = &n; b4 +=3; ///swap the values; tmpc = *b2; *b2 = *b4; *b4 = tmpc; Any other methods?

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• How to call a function though Control.BeginInvoke in a signal-slot-like fashion?

  - by Dimitri C.

  I'd like a delegate that calls a function in a different thread when it is invoked. Currently, I'm using the following implementation: delegate void someFunctionDelegate(); //... someFunctionDelegate callBackFunction = someForm.SomeFunction; someForm.Invoke(someFunctionDelegate); However, I'd like a more compact form, combining both the someForm instance and the SomeForm.SomeFunction member function. I'm thinking of something like this: var callBackFunction = new AsynchronousCrossThreadDelegate(someForm, SomeForm.SomeFunction); callBackFunction(); // Should call someForm.BeginInvoke(SomeForm.SomeFunction); Is there a way to do so in C#/.NET? Update I'm looking for a solution that will work for functions with 0 or more parameters.

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• basename() returning int?

  - by EB

  Probably something stupid I'm missing but, why am I getting this warning? static void foo(char *path) { char *bname; char *path2 = strdup(path); bname = basename(path2); (line with basename() call): warning: assignment makes pointer from integer without a cast Indeed, if I change to this, the warning goes away: bname = (char *)basename(path2); man 3 basename tells me: char *basename(char *path); Both dirname() and basename() return pointers to null-terminated strings. What gives?

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• delete & new in c++

  - by singh

  Hi This may be very simple question,But please help me. i wanted to know what exactly happens when i call new & delete , For example in below code char * ptr=new char [10]; delete [] ptr; call to new returns me memory address. Does it allocate exact 10 bytes on heap, Where information about size is stored.When i call delete on same pointer,i see in debugger that there are a lot of byte get changed before and after the 10 Bytes. Is there any header for each new which contain information about number of byte allocated by new. Thanks a lot

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• Prolog: find all numbers of unique digits that can be formed from a list of digits

  - by animo

  The best thing I could come up with so far is this function: numberFromList([X], X) :- digit(X), !. numberFromList(List, N) :- member(X, List), delete(List, X, LX), numberFromList(LX, NX), N is NX * 10 + X. where digit/1 is a function verifying if an atom is a decimal digit. The numberFromList(List, N) finds all the numbers that can be formed with all digits from List. E.g. [2, 3] -> 23, 32. but I want to get this result: [2, 3] -> 2, 3, 23, 32 I spent a lot of hours thinking about this and I suspect you might use something like append(L, _, List) at some point to get lists of lesser length. I would appreciate any contribution.

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• Lifetime of implicitly casted temporaries

  - by Answeror

  I have seen this question. It seems that regardless of the cast, the temporary object(s) will "survive" until the fullexpression evaluated. But in the following scenario: void foo(boost::tuple<const double&> n) { printf("%lf\n", n.get<0>()); } int main() { foo(boost::tuple<const double&>(2));//#1 foo(boost::make_tuple(2));//#2 return 0; } 1 run well, but 2 do not. And MSVC gave me a warning about 2: "reference member is initialized to a temporary that doesn't persist after the constructor exits" Now I am wondering why they both make a temporary "double" object and pass it to boost::tuple<const double&> and only 2 failed.

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• Is there a way to cause a new C++ class instance to fail, if certain conditions in the contructor ar

  - by Jim Fell

  As I understand it, when a new class is instantiated in C++, a pointer to the new class is returned, or NULL, if there is insufficient memory. I am writing a class that initializes a linked list in the constructor. If there is an error while initializing the list, I would like the class instantiator to return NULL. For example: MyClass * pRags = new MyClass; If the linked list in the MyClass constructor fails to initialize properly, I would like pRags to equal NULL. I know that I can use flags and additional checks to do this, but I would like to avoid that, if possible. Does anyone know of a way to do this? Thanks.

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• When I use WinForms (C#) designer in VS2010, it still generates code that StyleCop complains about.

  - by Hamish Grubijan

  Some problems that I recall (there may be more): Includes regions Does not use this. prefix for member variables and methods Includes comments like the one below ( having // by itself catches the eye of StyleCop) // // fileNameTextBox // If I make a change to the text, and then open the designer again, and screws up my previously perfected fruits of hard labor. How did / would you solve this problem? I heard but did not personally experience a similar problem with WPF. How did / would you fix that? Thanks.

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