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  • Java - Class type from inside static initialization block

    - by DutrowLLC
    Is it possible to get the class type from inside the static initialization block? This is a simplified version of what I currently have:: class Person extends SuperClass { String firstName; static{ // This function is on the "SuperClass": // I'd for this function to be able to get "Person.class" without me // having to explicitly type it in but "this.class" does not work in // a static context. doSomeReflectionStuff(Person.class); // IN "SuperClass" } } This is closer to what I am doing, which is to initialize a data structure that holds information about the object and its annotations, etc... Perhaps I am using the wrong pattern? public abstract SuperClass{ static void doSomeReflectionStuff( Class<?> classType, List<FieldData> fieldDataList ){ Field[] fields = classType.getDeclaredFields(); for( Field field : fields ){ // Initialize fieldDataList } } } public abstract class Person { @SomeAnnotation String firstName; // Holds information on each of the fields, I used a Map<String, FieldData> // in my actual implementation to map strings to the field information, but that // seemed a little wordy for this example static List<FieldData> fieldDataList = new List<FieldData>(); static{ // Again, it seems dangerous to have to type in the "Person.class" // (or Address.class, PhoneNumber.class, etc...) every time. // Ideally, I'd liken to eliminate all this code from the Sub class // since now I have to copy and paste it into each Sub class. doSomeReflectionStuff(Person.class, fieldDataList); } }

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  • non-copyable objects and value initialization: g++ vs msvc

    - by R Samuel Klatchko
    I'm seeing some different behavior between g++ and msvc around value initializing non-copyable objects. Consider a class that is non-copyable: class noncopyable_base { public: noncopyable_base() {} private: noncopyable_base(const noncopyable_base &); noncopyable_base &operator=(const noncopyable_base &); }; class noncopyable : private noncopyable_base { public: noncopyable() : x_(0) {} noncopyable(int x) : x_(x) {} private: int x_; }; and a template that uses value initialization so that the value will get a known value even when the type is POD: template <class T> void doit() { T t = T(); ... } and trying to use those together: doit<noncopyable>(); This works fine on msvc as of VC++ 9.0 but fails on every version of g++ I tested this with (including version 4.5.0) because the copy constructor is private. Two questions: Which behavior is standards compliant? Any suggestion of how to work around this in gcc (and to be clear, changing that to T t; is not an acceptable solution as this breaks POD types). P.S. I see the same problem with boost::noncopyable.

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  • C++: Construction and initialization order guarantees

    - by Helltone
    Hi, I have some doubts about construction and initialization order guarantees in C++. For instance, the following code has four classes X, Y, Z and W. The main function instantiates an object of class X. X contains an object of class Y, and derives from class Z, so both constructors will be called. Additionally, the const char* parameter passed to X's constructor will be implicitly converted to W, so W's constructor must also be called. What are the guarantees the C++ standard gives on the order of the calls to the copy constructors? Or, equivalently, this program is allowed to print? #include <iostream> class Z { public: Z() { std::cout << "Z" << std::endl; } }; class Y { public: Y() { std::cout << "Y" << std::endl; } }; class W { public: W(const char*) { std::cout << "W" << std::endl; } }; class X : public Z { public: X(const W&) { std::cout << "X" << std::endl; } private: Y y; }; int main(int, char*[]) { X x("x"); return 0; }

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  • How does this circle collision detection math work?

    - by Griffin
    I'm going through the wildbunny blog to learn about collision detection. I'm confused about how the vectors he's talking about come into play. Here's the part that confuses me: p = ||A-B|| – (r1+r2) The two spheres are penetrating by distance p. We would also like the penetration vector so that we can correct the penetration once we discover it. This is the vector that moves both circles to the point where they just touch, correcting the penetration. Importantly it is not only just a vector that does this, it is the only vector which corrects the penetration by moving the minimum amount. This is important because we only want to correct the error, not introduce more by moving too much when we correct, or too little. N = (A-B) / ||A-B|| P = N*p Here we have calculated the normalised vector N between the two centres and the penetration vector P by multiplying our unit direction by the penetration distance. I understand that p is the distance by which the circles penetrate, but I don't get what exactly N and P are. It seems to me N is just the coordinates of the 3rd point of the right trianlge formed by point A and B (A-B) then being divided by the hypotenuse of that triangle or distance between A and B (||A-B||). What's the significance of this? Also, what is the penetration vector used for? It seems to me like a movement that one of the circles would perform to get un-penetrated.

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  • why does array initialization in function other than main is temporary? [on hold]

    - by shafeeq
    This is the code in which i initialize array "turn[20]" in main as well as in function "checkCollisionOrFood()",the four values turn[0],turn[1],turn[2],turn[3] are initialized to zero in main function,rest are being intialized in "checkCollisionOrFood()".This is where fault starts.when i initialize turn[4]=0 in "checkCollisionOrFood()" and then access it anywhere,it remains 0 in any function,but! when i initialize next turn[] i.e turn[5],the value of turn[4] gets depleted .i.e turn[4] have garbage value.turn[20] is global variable,its index"head" is also global.I'm stuck.Plz help me get out of it.Ishall be highly obliged for this act of kindness.This is my excerpt of code unsigned short checkCollisionOrFood(){ head=(head+1)%20; if(turn[head-1]==0){ turn[head]=0; /this is where turn[] is iniliazized and if i access turn[head] here i.e just after iniliazition then it gives correct value but if i access its previous value means turn[head-1]then it gives garbage value/ rowHead=(rowHead+1)%8; if(!(address[colHead]&(1<<rowHead)))return 1; else if((address[colHead]&(1<<rowHead))&& (!((colHead==foody)&&(rowHead==foodx))))gameOver(); else return 0; } if(turn[head-1]==1){ turn[head]=1; colHead=(colHead+1)%8; if(!(address[colHead]&(1<<rowHead)))return 1; else if((address[colHead]&(1<<rowHead))&& (!((colHead==foody)&&(rowHead==foodx))))gameOver(); else return 0; } } void main(void) { turn[0]=0;turn[1]=0;turn[2]=0;turn[3]=0; /these values of turn[] are not changed irrespective of where they are accessed./ while (1) { if(checkCollisionOrFood()) { PORTB=(address[colHead] |=1<<rowHead); turnOffTail(); blink(); } else { PORTB=address[colHead]; createFood(); blink(); } } } Plz help me.

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  • Is DxScene the "WPF for Delphi"? Anyone used it?

    - by André Mussche
    I am playing with DxScene and VxScene: http://www.ksdev.com/dxscene/index.html It looks very nice and powerful: 3d accelerated vector graphics, cross plaform, nice effects, many 2d GUI controls (vector based), good scaling, transparency, rotating (x, y, z), 3d models, etc. Even with many effects, the CPU stays very low (0%)! http://www.ksdev.com/dxscene/snapshot/screen0.jpeg But can it be seen as a good WPF alternative for Delphi? And does anyone use it instead of normal Delphi VCL?

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  • Performance of vector::size() : is it as fast as reading a variable?

    - by zoli2k
    I have do an extensive calculation on a big vector of integers. The vector size is not changed during the calculation. The size of the vector is frequently accessed by the code. What is faster in general: using the vector::size() function or using helper constant vectorSize storing the size of the vector? I know that compilers usually able to inline the size() function when setting the proper compiler flags, however, making a function inline is something that a compiler may do but can not be forced.

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  • Vector [] vs copying

    - by sak
    What is faster and/or generally better? vector<myType> myVec; int i; myType current; for( i = 0; i < 1000000; i ++ ) { current = myVec[ i ]; doSomethingWith( current ); doAlotMoreWith( current ); messAroundWith( current ); checkSomeValuesOf( current ); } or vector<myType> myVec; int i; for( i = 0; i < 1000000; i ++ ) { doSomethingWith( myVec[ i ] ); doAlotMoreWith( myVec[ i ] ); messAroundWith( myVec[ i ] ); checkSomeValuesOf( myVec[ i ] ); } I'm currently using the first solution. There are really millions of calls per second and every single bit comparison/move is performance-problematic.

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  • binary_search not working for a vector<string>

    - by VaioIsBorn
    #include <iostream> #include <string> #include <vector> #include <algorithm> using namespace std; int main(void) { string temp; vector<string> encrypt, decrypt; int i,n, co=0; cin >> n; for(i=0;i<n;i++) { cin >> temp; encrypt.push_back(temp); } for(i=0;i<n;i++) { cin >> temp; decrypt.push_back(temp); } for(i=0;i<n;i++) { temp = encrypt[i]; if((binary_search(decrypt.begin(), decrypt.end(), temp)) == true) ++co; } cout << co << endl; return 0; } It reads two equal lists of strings and should print out how many of the words in the first list are also found in the second list, simple. Not giving me the expexted results and i think the problem is in binary_search. Can you tell me why ?

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  • C++ Array vs vector

    - by blue_river
    when using C++ vector, time spent is 718 milliseconds, while when I use Array, time is almost 0 milliseconds. Why so much performance difference? int _tmain(int argc, _TCHAR* argv[]) { const int size = 10000; clock_t start, end; start = clock(); vector<int> v(size*size); for(int i = 0; i < size; i++) { for(int j = 0; j < size; j++) { v[i*size+j] = 1; } } end = clock(); cout<< (end - start) <<" milliseconds."<<endl; // 718 milliseconds int f = 0; start = clock(); int arr[size*size]; for(int i = 0; i < size; i++) { for(int j = 0; j < size; j++) { arr[i*size+j] = 1; } } end = clock(); cout<< ( end - start) <<" milliseconds."<<endl; // 0 milliseconds return 0; }

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  • C++: Vector of objects vs. vector of pointers to new objects?

    - by metamemetics
    Hello, I am seeking to improve my C++ skills by writing a sample software renderer. It takes objects consisting of points in a 3d space and maps them to a 2d viewport and draws circles of varying size for each point in view. Which is better: class World{ vector<ObjectBaseClass> object_list; public: void generate(){ object_list.clear(); object_list.push_back(DerivedClass1()); object_list.push_back(DerivedClass2()); or... class World{ vector<ObjectBaseClass*> object_list; public: void generate(){ object_list.clear(); object_list.push_back(new DerivedClass1()); object_list.push_back(new DerivedClass2()); ?? Would be using pointers in the 2nd example to create new objects defeat the point of using vectors, because vectors automatically call the DerivedClass destructors in the first example but not in the 2nd? Are pointers to new objects necessary when using vectors because they handle memory management themselves as long as you use their access methods? Now let's say I have another method in world: void drawfrom(Viewport& view){ for (unsigned int i=0;i<object_list.size();++i){ object_list.at(i).draw(view); } } When called this will run the draw method for every object in the world list. Let's say I want derived classes to be able to have their own versions of draw(). Would the list need to be of pointers then in order to use the method selector (-) ?

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  • Are vector assignments copied by value or by reference in Google's Go language?

    - by Brian T Hannan
    In the following code, I create one peg puzzle then do a move on it which adds a move to its movesAlreadyDone vector. Then I create another peg puzzle then do a move on it which adds a move to its movesAlreadyDone vector. When I print out the values in that vector for the second one, it has the move in it from the first one along with the move from the second one. Can anyone tell me why it seems to be assigning by reference and not value? Are vector assignments copied by value or by reference in Google's Go language? package main import "fmt" import "container/vector" type Move struct { x0, y0, x1, y1 int } type PegPuzzle struct { movesAlreadyDone * vector.Vector; } func (p *PegPuzzle) InitPegPuzzle(){ p.movesAlreadyDone = vector.New(0); } func NewChildPegPuzzle(parent *PegPuzzle) *PegPuzzle{ retVal := new(PegPuzzle); retVal.movesAlreadyDone = parent.movesAlreadyDone; return retVal } func (p *PegPuzzle) doMove(move Move){ p.movesAlreadyDone.Push(move); } func (p *PegPuzzle) printPuzzleInfo(){ fmt.Printf("-----------START----------------------\n"); fmt.Printf("moves already done: %v\n", p.movesAlreadyDone); fmt.Printf("------------END-----------------------\n"); } func main() { p := new(PegPuzzle); cp1 := new(PegPuzzle); cp2 := new(PegPuzzle); p.InitPegPuzzle(); cp1 = NewChildPegPuzzle(p); cp1.doMove(Move{1,1,2,3}); cp1.printPuzzleInfo(); cp2 = NewChildPegPuzzle(p); cp2.doMove(Move{3,2,5,1}); cp2.printPuzzleInfo(); } Any help will be greatly appreciated. Thanks!

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  • How can I partition a vector?

    - by Karsten W.
    How can I build a function slice(x, n=2) which would return a list of vectors where each vector except maybe the last has size n, i.e. slice(letters, 10) would return list(c("a", "b", "c", "d", "e", "f", "g", "h", "i", "j"), c("k", "l", "m", "n", "o", "p", "q", "r", "s", "t"), c("u", "v", "w", "x", "y", "z")) ?

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  • vector drawing canvas in GWT

    - by Limbic System
    Are there are decent implementations of a vector graphics canvas in GWT? I would like to be draw arbitrary shapes and have them react to user input (mouse in/out/click/etc). There are wrappers for the HTML canvas, but that feature is not supported in older browsers (read: IE).

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  • Vector graphics on iPhone

    - by burki
    Hello! How you can use EPS files within your UIView. What do I have to do to display for example a EPS on the iPhone's screen? Do I need to convert it first to a PDF (if yes, how?)? Or are there any other way to bring vector graphics onto the iPhone? That would be very nice. Thanks.

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  • C++ Map of Vector of Structs?

    - by garsh0p
    So here's a snippet of my code: struct dv_nexthop_cost_pair { unsigned short nexthop; unsigned int cost; }; map<unsigned short, vector<struct dv_nexthop_cost_pair> > dv; I'm getting the following compiler error: error: ISO C++ forbids declaration of `map' with no type What's the proper way to declare this?

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  • Removing elements from C++ std::vector

    - by user219847
    What is the proper way to remove elements from a C++ vector while iterating through it? I am iterating over an array and want to remove some elements that match a certain condition. I've been told that it's a bad thing to modify it during traversal.

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