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• Trouble assigning a tr1::shared_ptr

  - by Max

  I've got a class that has a tr1::shared_ptr as a member, like so: class Foo { std::tr1::shared_ptr<TCODBsp> bsp; void Bar(); } In member function Bar, I try to assign it like this: bsp = newTCODBsp(x,y,w,h); g++ then gives me this error no match for ‘operator=’ in ‘((yarl::mapGen::MapGenerator*)this)->yarl::mapGen::MapGenerator::bsp = (operator new(40u), (<statement>, ((TCODBsp*)<anonymous>)))’ /usr/include/c++/4.4/tr1/shared_ptr.h:834: note: candidates are: std::tr1::shared_ptr<TCODBsp>& std::tr1::shared_ptr<TCODBsp>::operator=(const std::tr1::shared_ptr<TCODBsp>&) in my code, Foo is actually yarl::mapGen::MapGenerator. What am I doing wrong?

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• Draw 2 parallel lines

  - by Ben Martin

  How can I calculate the points to draw 2 parallel lines. I know the start and end points for the centre of the parallel lines. To makes thing a little bit harder, it needs to support straight and Bezier curved lines.

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• Which libraries use the "We Know Where You Live" optimization for std::make_shared?

  - by KnowItAllWannabe

  Over two years ago, Stephan T. Lavavej described a space-saving optimization he implemented in Microsoft's implementation of std::make_shared, and I know from speaking with him that Microsoft has nothing against other library implementations adopting this optimization. If you know for sure whether other libraries (e.g., for Gnu C++, Clang, Intel C++, plus Boost (for boost::make_shared)) have adopted this implementation, please contribute an answer. I don't have ready access to that many make_shared implementations, nor am I wild about digging into the bowels of the ones I have to see if they've implemented the WKWYL optimization, but I'm hoping that SO readers know the answers for some libraries off-hand. I know from looking at the code that as of Boost 1.52, the WKWYL optimization had not been implemented, but Boost is now up to version 1.55. Note that this optimization is different from std::make_shared's ability to avoid a dedicated heap allocation for the reference count used by std::shared_ptr. For a discussion of the difference between WKWYL and that optimication, consult this question.

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• Casting a container of shared_ptr

  - by Jamie Cook

  Hi all, I have a method void foo(list<shared_ptr<Base>>& myList); Which I'm trying to call with a two different types of lists, one of DerivedClass1 and one of DerivedClass2 list<shared_ptr<DerivedClass1>> myList1; foo(myList1); list<shared_ptr<DerivedClass2>> myList2; foo(myList2); However this obviously generates a compiler error error: a reference of type "std::list<boost::shared_ptr<Base>, std::allocator<boost::shared_ptr<Base>>> &" (not const-qualified) cannot be initialized with a value of type "std::list<boost::shared_ptr<DerivedClass1>, std::allocator<boost::shared_ptr<DerivedClass1>>>" Is there any easy way to cast a container of shared_ptr? Of alternate containers that can accomplish this?

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• How to systematically generate images from data?

  - by adamvickers

  I work for a performing arts nonprofit. We have seating charts for each of the theaters we work with; each seating chart shows the number of sections, the shape of each section, and the number of rows in each section. We'd like to create dynamic seating charts based on this info. We'd like them to look/feel kinda like this: http://www.fansnap.com/tickets/177754-on. But the tricky part is we'd like to be able to store all the info about each theater (the section names, shape/size of each section, and number of rows in each section) as data and then build a system that reads this data and uses it to create a dynamic map. I'm a life-long web developer, but I don't have have any experience with a difficult graphics problem like this. I realize it's a complex problem and I don't expect anyone to give me a complete answer here, but I would love direction on where I should be looking for more info. Is what I'm describing possible? Does this sort of technique have a name? Where can I learn more about how to accomplish this? What software should I use? Any info would be helpful.

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• Who can give me a link for the operator= of vector in MSDN?

  - by 8888q8888

  Who can give me a link for the operator= of vector in MSDN? Why I can only find operator[]? If operator= is just something default, like copy everything in A to B, how this following code works? vector<double> v(100,1); v = vector<double>(200,2); // if operator= is just a trivail version, how to make sure the old v get cleared?

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• How does one create a shared_ptr to pass to a function that takes a void *

  - by shaz

  That's pretty much it. I need to allocate memory and pass it to a function that takes a void *. I'd like to use a shared_ptr but I don't know how to do it.

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• `enable_shared_from_this` has a non-virtual destructor

  - by Shtééf

  I have a pet project with which I experiment with new features of the upcoming C++0x standard. While I have experience with C, I'm fairly new to C++. To train myself into best practices, (besides reading a lot), I have enabled some strict compiler parameters (using GCC 4.4.1): -std=c++0x -Werror -Wall -Winline -Weffc++ -pedantic-errors This has worked fine for me. Until now, I have been able to resolve all obstacles. However, I have a need for enable_shared_from_this, and this is causing me problems. I get the following warning (error, in my case) when compiling my code (probably triggered by -Weffc++): base class ‘class std::enable_shared_from_this<Package>’ has a non-virtual destructor So basically, I'm a bit bugged by this implementation of enable_shared_from_this, because: A destructor of a class that is intended for subclassing should always be virtual, IMHO. The destructor is empty, why have it at all? I can't imagine anyone would want to delete their instance by reference to enable_shared_from_this. But I'm looking for ways to deal with this, so my question is really, is there a proper way to deal with this? And: am I correct in thinking that this destructor is bogus, or is there a real purpose to it?

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• Force an object to be allocated on the heap

  - by Warren Seine

  A C++ class I'm writing uses shared_from_this() to return a valid boost::shared_ptr<>. Besides, I don't want to manage memory for this kind of object. At the moment, I'm not restricting the way the user allocates the object, which causes an error if shared_from_this() is called on a stack-allocated object. I'd like to force the object to be allocated with new and managed by a smart pointer, no matter how the user declares it. I thought it could be done through a proxy or an overloaded new operator, but I can't find a proper way of doing that. Is there a common design pattern for such usage? If it's not possible, how can I test it at compile time?

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• Custom deleters for std::shared_ptrs

  - by Kristian D'Amato

  Is it possible to use a custom deleter after creating a std::shared_ptr without using new? My problem is that object creation is handled by a factory class and its constructors & destructors are protected, which gives a compile error, and I don't want to use new because of its drawbacks. To elaborate: I prefer to create shared pointers like this, which doesn't let you set a custom deleter (I think): auto sp1 = make_shared<Song>(L"The Beatles", L"Im Happy Just to Dance With You"); Or I can create them like this, which does let met set a deleter through an argument: auto sp2(new Song, MyDeleterFunc); But the second one uses new, which AFAIK isn't as efficient as the top sort of allocation. Maybe this is clearer: is it possible to get the benefits of make_shared<> as well as a custom deleter? Would that mean having to write an allocator?

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• Adding and sorting a linked list in C

  - by user1202963

  In my assignment, I have to write a function that takes as arguments a pointer to a "LNode" structure and an integer argument. Then, I have to not only add that integer into the linked list, but also put place it so that the list is in proper ascending order. I've tried several various attempts at this, and this is my code as of posting. LNode* AddItem(LNode *headPtr, int newItem) { auto LNode *ptr = headPtr; ptr = malloc(sizeof(LNode)); if (headPtr == NULL) { ptr->value = newItem; ptr->next = headPtr; return ptr; } else { while (headPtr->value > newItem || ptr->next != NULL) { printf("While\n"); // This is simply to let me know how many times the loop runs headPtr = headPtr->next; } ptr->value = newItem; ptr->next = headPtr; return ptr; } } // end of "AddItem" When I run it, and try to insert say a 5 and then a 3, the 5 gets inserted, but then the while loop runs once and I get a segmentation fault. Also I cannot change the arguments as it's part of a skeletal code for this project. Thanks to anyone who can help. If it helps this is what the structure looks like typedef struct LNode { int value; struct LNode *next; } LNode;

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• What is the correct way of using an auto_ptr on dynamically allocated arrays?

  - by LoudNPossiblyRight

  If i use auto_ptr to hold a pointer to a dynamically allocated array, when the auto_ptr gets killed it will use a plain delete operation and not delete[] thus not deleting my allocated array. How can i (properly) use auto_ptr on dynamically allocated arrays? If this is not possible, is there another smart pointer alternative for dynamically allocated arrays? Thanks in advance.

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• sequential minimal optimization C++

  - by Anton

  Hello. I want to implement the method of SVM. But the problem appeared in his training. It was originally planned to use SMO, but did not find ready-made libraries for C++. If there is a ready, then share it. Thank you in advance. The problem of finding an object in the picture (probably human)

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• C++ destructor problem with boost::scoped_ptr

  - by bb-generation

  I have a question about the following code: #include <iostream> #include <boost/scoped_ptr.hpp> class Interface { }; class A : public Interface { public: A() { std::cout << "A()" << std::endl; } virtual ~A() { std::cout << "~A()" << std::endl; } }; Interface* get_a() { A* a = new A; return a; } int main() { { std::cout << "1" << std::endl; boost::scoped_ptr<Interface> x(get_a()); std::cout << "2" << std::endl; } std::cout << "3" << std::endl; } It creates the following output: 1 A() 2 3 As you can see, it doesn't call the destructor of A. The only way I see to get the destructor of A being called, is to add a destructor for the Interface class like this: virtual ~Interface() { } But I really want to avoid any Implementation in my Interface class and virtual ~Interface() = 0; doesn't work (produces some linker errors complaining about a non existing implementation of ~Interface(). So my question is: What do I have to change in order to make the destructor being called, but (if possible) leave the Interface as an Interface (only abstract methods).

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• Why isn't the boost::shared_ptr -> operator inlined?

  - by Alan

  Since boost::shared_ptr could be called very frequently and simply returns a pointer, isn't the -> operator a good candidate for being inlined? T * operator-> () const // never throws { BOOST_ASSERT(px != 0); return px; } Would a good compiler automatically inline this anyway? Should I lose any sleep over this? :-)

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• How to create lines with Athens?

  - by Kilon

  I have no clue how to create lines with Athens. I took a look at Cairo docs but I cant see how Athens is related to Cairo. http://zetcode.com/gfx/cairo/basicdrawing/ In the above link I cant find any equivalent for cairo_set_line_width(cr, 1); I tried to look inside Athens but is nowhere to be found. Overall I find the Athens architecture quite confusing though Cairo looks simple. Any idea how to makes this work ?

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• shared_ptr as class member

  - by idimba

  It's common to declared contained objects as a pointers to that class, while "forward declarating" them in header file. This in order to reduce physical dependencies in code. For example class B; // forward declaration class A { private: B* pB; }; Would it be good idea to declare such a member as shared_ptr, instead of naked pointer? I would prefer scoped_ptr, but AFAIKit it won't be in standard.

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• Why it's can be compiled in GNU/C++, can't compiled in VC++2010 RTM?

  - by volnet

  #include #include #include #include "copy_of_auto_ptr.h" #ifdef _MSC_VER #pragma message("#include ") #include // http://gcc.gnu.org/onlinedocs/gcc/Diagnostic-Pragmas.html#Diagnostic-Pragmas #endif /* case 1-4 is the requirement of the auto_ptr. which form http://ptgmedia.pearsoncmg.com/images/020163371X/autoptrupdate/auto_ptr_update.html */ /* case 1. (1) Direct-initialization, same type, e.g. */ std::auto_ptr source_int() { // return std::auto_ptr(new int(3)); std::auto_ptr tmp(new int(3)); return tmp; } /* case 2. (2) Copy-initialization, same type, e.g. */ void sink_int(std::auto_ptr p) { std::cout source_derived() { // return std::auto_ptr(new Derived()); std::auto_ptr tmp(new Derived()); return tmp; } /* case 4. (4) Copy-initialization, base-from-derived, e.g. */ void sink_base( std::auto_ptr p) { p-go(); } int main(void) { /* // auto_ptr */ // case 1. // auto_ptr std::auto_ptr p_int(source_int()); std::cout p_derived(source_derived()); p_derived-go(); // case 4. // auto_ptr sink_base(source_derived()); return 0; } In Eclipse(GNU C++.exe -v gcc version 3.4.5 (mingw-vista special r3)) it's two compile error: Description Resource Path Location Type initializing argument 1 of void sink_base(std::auto_ptr<Base>)' from result ofstd::auto_ptr<_Tp::operator std::auto_ptr<_Tp1() [with _Tp1 = Base, _Tp = Derived]' auto_ptr_ref_research.cpp auto_ptr_ref_research/auto_ptr_ref_research 190 C/C++ Problem Description Resource Path Location Type no matching function for call to `std::auto_ptr::auto_ptr(std::auto_ptr)' auto_ptr_ref_research.cpp auto_ptr_ref_research/auto_ptr_ref_research 190 C/C++ Problem But it's right in VS2010 RTM. Questions: Which compiler stand for the ISO C++ standard? The content of case 4 is the problem "auto_ptr & auto_ptr_ref want to resolve?"

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• Transform shape built of contour splines to simple polygons

  - by Cheery

  I've dumped glyphs from truetype file so I can play with them. They have shape contours that consist from quadratic bezier curves and lines. I want to output triangles for such shapes so I can visualize them for the user. Traditionally I might use libfreetype or scan-rasterise this kind of contours. But I want to produce extruded 3D meshes from the fonts and make other distortions with them. So, how to polygonise shapes consisting from quadratic bezier curves and lines? There's many contours that form the shape together. Some contours are additive and others are subtractive. The contours are never open. They form a loop. (Actually, I get only contour vertices from ttf glyphs, those vertices define whether they are part of the curve or not. Even though it is easy to decompose these into bezier curves and lines, knowing the data is represented this way may be helpful for polygonizing the contours to triangles)

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• How can I draw the control points of a Bézier Path in Java?

  - by Sanoj

  I have created a Path of Bézier curves and it works fine to draw the path. But I don't know How I can draw the Control Points together with the Path. Is that possible or do I have to keep track of them in another datastructure? I am creating the path with: Path2D.Double path = new Path2D.Double(); path.moveTo(0,0); path.curveTo(5, 6, 23, 12, 45, 54); path.curveTo(34, 23, 12, 34, 2, 3); And drawing it with: g2.draw(path);

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• Boost Shared Pointers and Memory Management

  - by Izza

  I began using boost rather recently and am impressed by the functionality and APIs provided. In using boost::shared_ptr, when I check the program with Valgrind, I found a considerable number of "Still reachable" memory leaks. As per the documentation of Valgrind, these are not a problem. However, since I used to use the standard C++ library only, I always made sure that any program written is completely free from memory leaks. My question is, are these memory leaks something to worry about? I tried using reset(), however it only decrements the reference count, doesn't deallocate memory. Can I safely ignore these, or any way to forcibly deallocate the memory allocated by boost::shared_ptr? Thank you.

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• Iterating through boost ptr_vector

  - by Ockonal

  Hello, I have a ptr_vector list of my own objects. Something like this: boost::ptr_vector<SomeClass> *list; list.push_back(new SomeClass()>; ... BOOST_FOREACH(SomeClass *tempObj, list) // [x] { tempObj->... } >‘boost::ptr_vector<SomeClass>*’ is not a class, struct, or union type

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• Best way in Python to determine all possible intersections in a matrix?

  - by ssweens

  So if I have a matrix (list of lists) of unique words as my column headings, document ids as my row headings, and a 0 or 1 as the values if the word exists in that particular document. What I'd like to know is how to determine all the possible combinations of words and documents where more than one word is in common with more than one document. So something like: [[Docid_3, Docid_5], ['word1', 'word17', 'word23']], [[Docid_3, Docid_9, Docid_334], ['word2', 'word7', 'word23', 'word68', 'word982']], and so on for each possible combination. Would love a solution that provides the complete set of combinations and one that yields only the combinations that are not a subset of another, so from the example, not [[Docid_3, Docid_5], ['word1', 'word17']] since it's a complete subset of the first example. I feel like there is an elegant solution that just isn't coming to mind and the beer isn't helping. Thanks.

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• C++ volatile required when spinning on boost::shared_ptr operator bool()?

  - by JaredC

  I have two threads referencing the same boost::shared_ptr: boost::shared_ptr<Widget> shared; On thread is spinning, waiting for the other thread to reset the boost::shared_ptr: while(shared) boost::thread::yield(); And at some point the other thread will call: shared.reset(); My question is whether or not I need to declare the shared pointer as volatile to prevent the compiler from optimizing the call to shared.operator bool() out of the loop and never detecting the change? I know that if I were simply looping on a variable, waiting for it to reach 0 I would need volatile, but I'm not sure if boost::shared_ptr is implemented in such a way that it is not necessary here.

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• Why is std::tr1::shared_ptr<>.reset() so expensive?

  - by Paul Oyster

  Profiling some code that heavily uses shared_ptrs, I discovered that reset() was surprisingly expensive. For example: struct Test { int i; Test() { this->i = 0; } Test(int i) { this->i = i; } } ; ... auto t = make_shared<Test>(1); ... t.reset(somePointerToATestObject); Tracing the reset() in the last line (under VC++ 2010), I discovered that it creates a new reference-counting object. Is there a cheaper way, that reuses the existing ref-count and does not bother the heap?

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