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• C# object (2 numbers) performing 2 calculations

  - by Chris

  I have a couple questions about creating a object (2 values) and how to "call" it. Initializing the object with: Tweetal t1, t2, t3, t4, t5, t6; t1 = new Tweetal(); //a: 0 , b = 0 t2 = new Tweetal(-2); //a: -2, b = -2 t3 = new Tweetal(5, 17); //a: 5, b = 17 t4 = new Tweetal(t3); //a:5, b = 17 Console.Write("t1 = " + t1); Console.Write("\tt2 = " + t2); Console.Write("\tt3 = " + t3); Console.Write("\tt4 = " + t4); Console.WriteLine("\n"); t1 = t1.Som(t2); t4 = t2.Som(t2); //...... Now the 2 things i want to do with this object are taking the SUM and the SUMNumber: Sum: t4 = t2.sum(t3); (this would result in t4: a:3 (-2+5), b: 15(-2+17) SumNumber: t1 = t3.sum(8) (this would result in t1: a:13 , b:25) Next is my code for the object (in a separate class), but how exactly do i perform the simple sum calculation when i call up for example t2 etc... public class Tweetal: Object { private int a; private int b; public Tweetal() { //??? //Sum(...,...) } public Tweetal(int a) { //??? //Sum(...,...) } public Tweetal(int a, int b) { //??? } public Tweetal(Tweetal //....) // to call upton the object if i request t1, t2, t3,... insteed of a direct number value) { // ???? } public void Sum(int aValue, int bValue) { //a = ??? //b = ??? //Sum(...,...) } public void SumNumber(int aValue, int bValue) { } public override string ToString() { return string.Format("({0}, {1})", a, b); }/*ToString*/ }

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• problem with "select new Object ... join ... where"

  - by jacob

  Hi, I'm having a problem with an HQL query Three classes ClassOne is my BusinessObject public class ClassOne { private int id; private int status; private Set<ClassTwo> classTwos; + other fields/getters/setters/constructor etc } ClassTwo is referenced in a set of ClassOne and is kind of the history of an object of ClassOne public class ClassTwo { private int id; private int oldStatus; private int newStatus; private String message; //+ getters/setters/constructor etc } ClassThree is my DTO/VO with just one classTwo (not the whole history) public class ClassThree { private int id; private int status; private ClassTwo classTwo; public ClassThree(int pId, int pStatus, ClassTwo pClassTwo) { id=pId; status=pStatus; classTwo=pClassTwo; } //+ getters/setters etc } Now I'd like to create an HQL query like this: I'd like to get all objects of ClassThree with a certain status and if it exists the newest ClassTwo with a certain newStatus. For example: I'd like to get all the DTOs (ClassThree) of ClassOne whose status is now 1, but earlier in their history it has been 2 and I'd like to have the latest ClassTwo object which has 2 as newStatus. SELECT new ClassThree(c1.id, c1.status, c2) FROM ClassOne c1 LEFT JOIN c1.classtwos c2 (...) and (...) is where I don't know what to do, I'm not even sure if it's a join / join fetch Looked around and tried quite a lot already, but no clue. Especially with the join fetch I get some Hibernate errors like org.hibernate.QueryException: query specified join fetching, but the owner of the fetched association was not present in the select list. Fetching the BusinessObject like that is no problem SELECT distinct(c1) FROM ClassOne c1 LEFT OUTER JOIN FETCH c1.classtwos c2 and I get the ClassTwos as my field. Thanks in advance, Jacob P.S.: One thing might be important, ClassTwo has no reference to ClassOne!!

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• how to make a CUDA Histogram kernel?

  - by kitw

  Hi all, I am writing a CUDA kernel for Histogram on a picture, but I had no idea how to return a array from the kernel, and the array will change when other thread read it. Any possible solution for it? __global__ void Hist( TColor *dst, //input image int imageW, int imageH, int*data ){ const int ix = blockDim.x * blockIdx.x + threadIdx.x; const int iy = blockDim.y * blockIdx.y + threadIdx.y; if(ix < imageW && iy < imageH) { int pixel = get_red(dst[imageW * (iy) + (ix)]); //this assign specific RED value of image to pixel data[pixel] ++; // ?? problem statement ... } } @para d_dst: input image TColor is equals to float4. @para data: the array for histogram size [255] extern "C" void cuda_Hist(TColor *d_dst, int imageW, int imageH,int* data) { dim3 threads(BLOCKDIM_X, BLOCKDIM_Y); dim3 grid(iDivUp(imageW, BLOCKDIM_X), iDivUp(imageH, BLOCKDIM_Y)); Hist<<<grid, threads>>>(d_dst, imageW, imageH, data); }

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• Please help with my twodimensional array source code

  - by Baiba

  Here is what i have done but i have some questions: class masivins { public static void main (String args[]) { int mas[][] = {{0, 2, 7, 0, 8, 5, 3}, {0, 4, 0, 6, 0, 0, 0}, {0, 0, 0, 0, 3, 0, 0}, {7, 0, 0, 9, 1, 0, 7}, {5, 0, 4, 0, 0, 2, 0}}; int nulmas[] = new int [7]; int nul=0; for(int j=0; j<7; j++) { nul=0; for(int i=0; i<5; i++) { if(mas[i][j]==0) { nul++; } } nulmas[j]=nul; } for(int i=0; i<5; i++) { for(int j=0; j<7; j++) { System.out.println(mas[i][j]); } System.out.println(); } System.out.println(); for(int i=0; i<5; i++) { System.out.println("Zeros in each array column: " + nulmas[i]); } System.out.println(); } } so my questions are: 1) why after running project there are only 5 "Zeros in each array column....." shown? 2) what and where i need to change in this code to get out the number of column in which zeros are least?

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• Strange overloading rules in C++

  - by bucels

  I'm trying to compile this code with GCC 4.5.0: #include <algorithm> #include <vector> template <typename T> void sort(T, T) {} int main() { std::vector<int> v; sort(v.begin(), v.end()); } But it doesn't seem to work: $ g++ -c nm.cpp nm.cpp: In function ‘int main()’: nm.cpp:9:28: error: call of overloaded ‘sort(std::vector<int>::iterator, std::vector<int>::iterator)’ is ambiguous nm.cpp:4:28: note: candidates are: void sort(T, T) [with T = __gnu_cxx::__normal_iterator<int*, std::vector<int> >] /usr/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../../include/c++/4.5.0/bits/stl_algo.h:5199:69: note: void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<int*, std::vector<int> >] Comeau compiles this code without errors. (4.3.10.1 Beta2, strict C++03, no C++0x) Is this valid C++?

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• Operator+ for a subtype of a template class.

  - by baol

  I have a template class that defines a subtype. I'm trying to define the binary operator+ as a template function, but the compiler cannot resolve the template version of the operator+. #include <iostream> template<typename other_type> struct c { c(other_type v) : cs(v) {} struct subtype { subtype(other_type v) : val(v) {} other_type val; } cs; }; template<typename other_type> typename c<other_type>::subtype operator+(const typename c<other_type>::subtype& left, const typename c<other_type>::subtype& right) { return typename c<other_type>::subtype(left.val + right.val); } // This one works // c<int>::subtype operator+(const c<int>::subtype& left, // const c<int>::subtype& right) // { return c<int>::subtype(left.val + right.val); } int main() { c<int> c1 = 1; c<int> c2 = 2; c<int>::subtype cs3 = c1.cs + c2.cs; std::cerr << cs3.val << std::endl; } I think the reason is because the compiler (g++4.3) cannot guess the template type so it's searching for operator+<int> instead of operator+. What's the reason for that? What elegant solution can you suggest?

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• Read large amount of data from file in Java

  - by Crozin

  Hello I've got text file that contains 1 000 002 numbers in following formation: 123 456 1 2 3 4 5 6 .... 999999 100000 Now I need to read that data and allocate it to int variables (the very first two numbers) and all the rest (1 000 000 numbers) to an array int[]. It's not a hard task, but - it's horrible slow. My first attempt was java.util.Scanner: Scanner stdin = new Scanner(new File("./path")); int n = stdin.nextInt(); int t = stdin.nextInt(); int array[] = new array[n]; for (int i = 0; i < n; i++) { array[i] = stdin.nextInt(); } It works as excepted but it takes about 7500 ms to execute. I need to fetch that data in up to several hundred of milliseconds. Then I tried java.io.BufferedReader: Using BufferedReader.readLine() and String.split() I got the same results in about 1700 ms, but it's still too many. How can I read that amount of data in less that 1 second? The final result should be equal to: int n = 123; int t = 456; int array[] = { 1, 2, 3, 4, ..., 999999, 100000 };

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• Unsure how to come up with a good design

  - by Mewzer

  Hello there, I am having trouble coming up with a good design for a group of classes and was hoping that someone could give me some guidance on best practices. I have kept the classes and member functions generic to make the problem simpler. Essentially, I have three classes (lets call them A, B, and C) as follows: class A { ... int GetX( void ) const { return x; }; int GetY( void ) const { return y; }; private: B b; // NOTE: A "has-a" B int x; int y; }; class B { ... void SetZ( int value ) { z = value }; private: int z; C c; // NOTE: B "has-a" C }; class C { private: ... void DoSomething(int x, int y){ ... }; void DoSomethingElse( int z ){ ... }; }; My problem is as follows: Class A uses its member variables "x" and "y" a lot internally. Class B uses its member variable "z" a lot internally. Class B needs to call C::DoSomething(), but C::DoSomething() needs the values of X and Y in class A passed in as arguments. C::DoSomethingElse() is called from say another class (e.g. D), but it needs to invoke SetZ() in class B!. As you can see, it is a bit of a mess as all the classes need information from one another!. Are there any design patterns I can use?. Any ideas would be much appreciated ....

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• Insert Into Two SQL Tables From XML Maintaining Relationship

  - by Thx

  I am looking to insert records from xml into two different tables. For example <Root> <A> <AValue>1</AValue> <Children> <B> <BValue>2</BValue> </B> </Children> </A> </Root> Would insert a record into table A AID AValue # 1 also insert a record into table B BID AID BValue # #(Same as AID Above) 2 I have this DECLARE @idoc INT DECLARE @doc NVARCHAR(MAX) SET @doc = ' <Root> <A> <AValue>1</AValue> <Children> <B> <BValue>2</BValue> </B> </Children> </A> </Root> ' EXEC sp_xml_preparedocument @idoc OUTPUT, @doc CREATE TABLE #A ( AID INT IDENTITY(1, 1) , AValue INT ) INSERT INTO #A SELECT * FROM OPENXML (@idoc, '/Root/A',2) WITH (AValue INT ) CREATE TABLE #B ( BID INT IDENTITY(1, 1) , AID INT , BValue INT ) INSERT INTO #B SELECT * FROM OPENXML (@idoc, '/Root/A/Children/B',2) WITH ( AID INT, BValue INT ) SELECT * FROM #A SELECT * FROM #B DROP TABLE #A DROP TABLE #B Thanks!

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• Top n items in a List ( including duplicates )

  - by Krishnan

  Trying to find an efficient way to obtain the top N items in a very large list, possibly containing duplicates. I first tried sorting & slicing, which works. But this seems unnnecessary. You shouldn't need to sort a very large list if you just want the top 20 members. So I wrote a recursive routine which builds the top-n list. This also works, but is very much slower than the non-recursive one! Question: Which is my second routine (elite2) so much slower than elite, and how do I make it faster ? My code is attached below. Thanks. import scala.collection.SeqView import scala.math.min object X { def elite(s: SeqView[Int, List[Int]], k:Int):List[Int] = { s.sorted.reverse.force.slice(0,min(k,s.size)) } def elite2(s: SeqView[Int, List[Int]], k:Int, s2:List[Int]=Nil):List[Int] = { if( k == 0 || s.size == 0) s2.reverse else { val m = s.max val parts = s.force.partition(_==m) val whole = if( parts._1.size > 1) parts._1.tail:::parts._2 else parts._2 elite2( whole.view, k-1, m::s2 ) } } def main(args:Array[String]) = { val N = 1000000/3 val x = List(N to 1 by -1).flatten.map(x=>List(x,x,x)).flatten.view println(elite2(x,20)) println(elite(x,20)) } }

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• why doesnt this program print?

  - by Alex

  What I'm trying to do is to print my two-dimensional array but i'm lost. The first function is running perfect, the problem is the second or maybe the way I'm passing it to the "Print" function. #include <stdio.h> #include <stdlib.h> #define ROW 2 #define COL 2 //Memory allocation and values input void func(int **arr) { int i, j; arr = (int**)calloc(ROW,sizeof(int*)); for(i=0; i < ROW; i++) arr[i] = (int*)calloc(COL,sizeof(int)); printf("Input: \n"); for(i=0; i<ROW; i++) for(j=0; j<COL; j++) scanf_s("%d", &arr[i][j]); } //This is where the problem begins or maybe it's in the main void print(int **arr) { int i, j; for(i=0; i<ROW; i++) { for(j=0; j<COL; j++) printf("%5d", arr[i][j]); printf("\n"); } } void main() { int *arr; func(&arr); print(&arr); //maybe I'm not passing the arr right ? }

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• Finding minimum value in a Map

  - by Sunny

  I have a map and I want to find the minimum value (right hand side) in the map. Right now here is how I did it bool compare(std::pair<std::string ,int> i, pair<std::string, int> j) { return i.second < j.second; } //////////////////////////////////////////////////// std::map<std::string, int> mymap; mymap["key1"] = 50; mymap["key2"] = 20; mymap["key3"] = 100; std::pair<char, int> min = *min_element(mymap.begin(), mymap.end(), compare); std::cout << "min " << min.second<< " " << std::endl; This works fine and I'm able to get the minimum value the problem is when I put this code inside my class it doesn't seem to work int MyClass::getMin(std::map<std::string, int> mymap) { std::pair<std::string, int> min = *min_element(mymap.begin(), mymap.end(), (*this).compare); //error probably due to this return min.second; } bool MyClass::compare( std::pair<std::string, int> i, std::pair<std::string, int> j) { return i.second < j.second; } Also is there a better solution not involving to writing the additional compare function

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• Clicking mouse by sending messages

  - by Frank Meulenaar

  I'm trying to send mouse clicks to a program. As I don't want the mouse to move, I don't want to use SendInput or mouse_event, and because the window that should receive the clicks doesn't really use Buttons or other GUI events, I can't send messages to these buttons. I'm trying to get this working using SendMessage, but for some reason it doesn't work. Relevant code is (in C#, but tried Java with jnative as well), trying this on Vista [DllImport("user32.dll", CharSet=CharSet.Auto)] public static extern int SendMessage(IntPtr A_0, int A_1, int A_2, int A_3); static int WM_CLOSE = 0x10; static int WM_LBUTTONDOWN = 0x201; static int WM_LBUTTONUP = 0x202; public static void click(IntPtr hWnd, int x, int y) { SendMessage(hWnd, WM_LBUTTONDOWN, 1, ((x << 0x10) ^ y)); SendMessage(hWnd, WM_LBUTTONUP, 0, ((x << 0x10) ^ y)); } public static void close(IntPtr hWnd) { SendMessage(hWnd, WM_CLOSE, 0, 0); } The close works fine, but the click doesn't do anything.

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• Imbricated C++ template

  - by gregseth

  I have the following pattern: template <int a, int b> class MyClass { template <int c> MyClass<a, c> &operator*(MyClass<c, b> const &other) const; }; // ../.. template <int a, int b> template <int c> MyClass<a, c> &MyClass<a, b>::operator*(MyClass<c, b> const &other) const { MyClass<a, c> result; // ..do stuff.. return result; } It doesn't compile, the error message is Error C2975. invalid template argument 'number', constant expression expected. If I replace template <int c> by template <int c, int d> and use it accordignly, it works fine. But I want d to be the same value as b. My questions: Why the example doesn't work? How can I enforce d to be the same than b? Thanks.

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• Dynamic Array of Objects Sans Vector Class

  - by Connor Black

  I am doing a homework assignment for my summer OO class and we need to write two classes. One is called Sale and the other is called Register. I've written my Sale class; here's the .h file: enum ItemType {BOOK, DVD, SOFTWARE, CREDIT}; class Sale { public: Sale(); // default constructor, // sets numerical member data to 0 void MakeSale(ItemType x, double amt); ItemType Item(); // Returns the type of item in the sale double Price(); // Returns the price of the sale double Tax(); // Returns the amount of tax on the sale double Total(); // Returns the total price of the sale void Display(); // outputs sale info private: double price; // price of item or amount of credit double tax; // amount of sales tax double total; // final price once tax is added in. ItemType item; // transaction type }; For the Register class we need to include a dynamic array of Sale objects in our member data. We cannot use the vector class. How is this done? Here's my 'Register' '.h' class Register{ public: Register(int ident, int amount); ~Register(); int GetID(){return identification;} int GetAmount(){return amountMoney;} void RingUpSale(ItemType item, int basePrice); void ShowLast(); void ShowAll(); void Cancel(); int SalesTax(int n); private: int identification; int amountMoney; };

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• C++ Inheritance and Constructors

  - by DizzyDoo

  Hello, trying to work out how to use constructors with an inherited class. I know this is very much wrong, I've been writing C++ for about three days now, but here's my code anyway: clientData.h, two classes, ClientData extends Entity : #pragma once class Entity { public: int x, y, width, height, leftX, rightX, topY, bottomY; Entity(int x, int y, int width, int height); ~Entity(); }; class ClientData : public Entity { public: ClientData(); ~ClientData(); }; and clientData.cpp, which contains the functions: #include <iostream> #include "clientData.h" using namespace std; Entity::Entity(int x, int y, int width, int height) { this->x = x; this->y = y; this->width = width; this->height = height; this->leftX = x - (width/2); this->rightX = x + (width/2); this->topY = y - (height/2); this-bottomY = y + (height/2); } Entity::~Entity() { cout << "Destructing.\n"; } ClientData::ClientData() { cout << "Client constructed."; } ClientData::~ClientData() { cout << "Destructing.\n"; } and finally, I'm creating a new ClientData with: ClientData * Data = new ClientData(32,32,32,16); Now, I'm not surprised my compiler shouts errors at me, so how do I pass the arguments to the right classes? The first error (from MVC2008) is error C2661: 'ClientData::ClientData' : no overloaded function takes 4 arguments and the second, which pops up whatever changes I seem to make is error C2512: 'Entity' : no appropriate default constructor available Thanks.

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• JAVA : How to get the positions of all matches in a String?

  - by user692704

  I have a text document and a query (the query could be more than one word). I want to find the position of all occurrences of the query in the document. I thought of the documentText.indexOf(query) and using regular expression but I could not make it work. I end up with the following method: First, I have create a dataType called QueryOccurrence public class QueryOccurrence implements Serializable{ public QueryOccurrence(){} private int start; private int end; public QueryOccurrence(int nameStart,int nameEnd,String nameText){ start=nameStart; end=nameEnd; } public int getStart(){ return start; } public int getEnd(){ return end; } public void SetStart(int i){ start=i; } public void SetEnd(int i){ end=i; } } Then, I have used this datatype in the following method: public static List<QueryOccurrence>FindQueryPositions(String documentText, String query){ // Normalize do the following: lower case, trim, and remove punctuation String normalizedQuery = Normalize.Normalize(query); String normalizedDocument = Normalize.Normalize(documentText); String[] documentWords = normalizedDocument.split(" ");; String[] queryArray = normalizedQuery.split(" "); List<QueryOccurrence> foundQueries = new ArrayList(); QueryOccurrence foundQuery = new QueryOccurrence(); int index = 0; for (String word : documentWords) { if (word.equals(queryArray[0])){ foundQuery.SetStart(index); } if (word.equals(queryArray[queryArray.length-1])){ foundQuery.SetEnd(index); if((foundQuery.End()-foundQuery.Start())+1==queryArray.length){ //add the found query to the list foundQueries.add(foundQuery); //flush the foundQuery variable to use it again foundQuery= new QueryOccurrence(); } } index++; } return foundQueries; } This method return a list of all occurrence of the query in the document each one with its position. Could you suggest any easer and faster way to accomplish this task. Thanks

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• Changing Value of Array Pointer When Passed to a Function

  - by ZAX

  I have a function which receives both the array, and a specific instance of the array. I try to change the specific instance of the array by accessing one of its members "color", but it does not actually change it, as can be seen by debugging (checking the value of color after function runs in the main program). I am hoping someone can help me to access this member and change it. Essentially I need the instance of the array I'm specifying to be passed by reference if nothing else, but I'm hoping there is an easier way to accomplish what I'm trying to do. Here's the structures: typedef struct adjEdge{ int vertex; struct adjEdge *next; } adjEdge; typedef struct vertex{ int sink; int source; int color; //0 will be white, 1 will be grey, 5 will be black int number; adjEdge *nextVertex; } vertex; And here is the function: void walk(vertex *vertexArray, vertex v, int source, maxPairing *head) { int i; adjEdge *traverse; int moveVertex; int sink; traverse = vertexArray[v.number-1].nextVertex; if(v.color != 5 && v.sink == 5) { sink = v.number; v.color = 5; addMaxPair(head, source, sink); } else { walk(vertexArray, vertexArray[traverse->vertex-1], source, head); } } In particular, v.color needs to be changed to a 5, that way later after recursion the if condition blocks it.

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• trying to switch beginning of an array with another

  - by user1874574

  I have a problem where i am trying to swap two arrays so that they switch beginnings. example: array 1 = (1,2,3,4,5,6,7,8) and array 2 = (11,12,13,14,15,16,17,18) i want to end up with the first array being (11,12,13,14,5,6,7,8) and i want the second array to be (1,2,3,4,15,16,17,18) but for some reason i end up with 1=(11,12,13,14,5,6,7,8) and 2=(11,12,13,14,15,16,17,18) my code is provided below, what am i doing wrong? public static void Mutate(Genetic lowest, Genetic secondLowest) { int halfway = (lowest.getPopulation().length)/2; int[] one = lowest.getPopulation(); int[] two = secondLowest.getPopulation(); int[] temp = secondLowest.getPopulation(); int[] temp2 = lowest.getPopulation(); for(int i = 0; i < halfway; i++){ temp[i] = one[i]; } lowest.setPopulation(temp); for(int i = 0; i < lowest.getPopulation().length; i++){ System.out.print(temp[i]); } System.out.println(); for(int i = 0; i < halfway; i++){ temp2[i] = two[i]; } for(int i = 0; i < lowest.getPopulation().length; i++){ System.out.print(temp2[i]); } }

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• Friendly way to override `const`-overloaded member function?

  - by xtofl

  Given a base class class A { int i; public: int& f(){ return i;} const int& f() const { return i;} }; And a sub class class ConstA : private A { public: const int& f() const { return A::f(); } }; Is there a wrist-friendly way to access the ConstA::f method on a non-const variable? ConstA ca; int i = ca.f(); // compile error: int& A::f() is not accessible since A is privately inherited int j = static_cast<const ConstA&>(ca).f(); // this works, but it hurts a little... Or is it so ugly since hiding A::f generally is a bad idea, violating the Liskov Substitution Principle: any subclass of A must at least be capable of all A's functionality? void set( A& a, int i ) { a.f() = i; } class ConstA2 : public A { private: int& f(){ return A::f(); } }; ConstA2 ca2; set( ca2, 1 ); (Note: this question popped up while thinking about this question)

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• Diving into OpenStack Network Architecture - Part 1

  - by Ronen Kofman

  v\:* {behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} w\:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);} rkofman Normal rkofman 83 3045 2014-05-23T21:11:00Z 2014-05-27T06:58:00Z 3 1883 10739 Oracle Corporation 89 25 12597 12.00 140 Clean Clean false false false false EN-US X-NONE HE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:Arial; mso-bidi-theme-font:minor-bidi; mso-bidi-language:AR-SA;} Before we begin OpenStack networking has very powerful capabilities but at the same time it is quite complicated. In this blog series we will review an existing OpenStack setup using the Oracle OpenStack Tech Preview and explain the different network components through use cases and examples. The goal is to show how the different pieces come together and provide a bigger picture view of the network architecture in OpenStack. This can be very helpful to users making their first steps in OpenStack or anyone wishes to understand how networking works in this environment.  We will go through the basics first and build the examples as we go. According to the recent Icehouse user survey and the one before it, Neutron with Open vSwitch plug-in is the most widely used network setup both in production and in POCs (in terms of number of customers) and so in this blog series we will analyze this specific OpenStack networking setup. As we know there are many options to setup OpenStack networking and while Neturon + Open vSwitch is the most popular setup there is no claim that it is either best or the most efficient option. Neutron + Open vSwitch is an example, one which provides a good starting point for anyone interested in understanding OpenStack networking. Even if you are using different kind of network setup such as different Neutron plug-in or even not using Neutron at all this will still be a good starting point to understand the network architecture in OpenStack. The setup we are using for the examples is the one used in the Oracle OpenStack Tech Preview. Installing it is simple and it would be helpful to have it as reference. In this setup we use eth2 on all servers for VM network, all VM traffic will be flowing through this interface.The Oracle OpenStack Tech Preview is using VLANs for L2 isolation to provide tenant and network isolation. The following diagram shows how we have configured our deployment: This first post is a bit long and will focus on some basic concepts in OpenStack networking. The components we will be discussing are Open vSwitch, network namespaces, Linux bridge and veth pairs. Note that this is not meant to be a comprehensive review of these components, it is meant to describe the component as much as needed to understand OpenStack network architecture. All the components described here can be further explored using other resources. Open vSwitch (OVS) In the Oracle OpenStack Tech Preview OVS is used to connect virtual machines to the physical port (in our case eth2) as shown in the deployment diagram. OVS contains bridges and ports, the OVS bridges are different from the Linux bridge (controlled by the brctl command) which are also used in this setup. To get started let’s view the OVS structure, use the following command: # ovs-vsctl show 7ec51567-ab42-49e8-906d-b854309c9edf     Bridge br-int         Port br-int             Interface br-int type: internal         Port "int-br-eth2"             Interface "int-br-eth2"     Bridge "br-eth2"         Port "br-eth2"             Interface "br-eth2" type: internal         Port "eth2"             Interface "eth2"         Port "phy-br-eth2"             Interface "phy-br-eth2" ovs_version: "1.11.0" We see a standard post deployment OVS on a compute node with two bridges and several ports hanging off of each of them. The example above is a compute node without any VMs, we can see that the physical port eth2 is connected to a bridge called “br-eth2”. We also see two ports "int-br-eth2" and "phy-br-eth2" which are actually a veth pair and form virtual wire between the two bridges, veth pairs are discussed later in this post. When a virtual machine is created a port is created on one the br-int bridge and this port is eventually connected to the virtual machine (we will discuss the exact connectivity later in the series). Here is how OVS looks after a VM was launched: # ovs-vsctl show efd98c87-dc62-422d-8f73-a68c2a14e73d     Bridge br-int         Port "int-br-eth2"             Interface "int-br-eth2"         Port br-int             Interface br-int type: internal         Port "qvocb64ea96-9f" tag: 1             Interface "qvocb64ea96-9f"     Bridge "br-eth2"         Port "phy-br-eth2"             Interface "phy-br-eth2"         Port "br-eth2"             Interface "br-eth2" type: internal         Port "eth2"             Interface "eth2" ovs_version: "1.11.0" Bridge "br-int" now has a new port "qvocb64ea96-9f" which connects to the VM and tagged with VLAN 1. Every VM which will be launched will add a port on the “br-int” bridge for every network interface the VM has. Another useful command on OVS is dump-flows for example: # ovs-ofctl dump-flows br-int NXST_FLOW reply (xid=0x4): cookie=0x0, duration=735.544s, table=0, n_packets=70, n_bytes=9976, idle_age=17, priority=3,in_port=1,dl_vlan=1000 actions=mod_vlan_vid:1,NORMAL cookie=0x0, duration=76679.786s, table=0, n_packets=0, n_bytes=0, idle_age=65534, hard_age=65534, priority=2,in_port=1 actions=drop cookie=0x0, duration=76681.36s, table=0, n_packets=68, n_bytes=7950, idle_age=17, hard_age=65534, priority=1 actions=NORMAL As we see the port which is connected to the VM has the VLAN tag 1. However the port on the VM network (eth2) will be using tag 1000. OVS is modifying the vlan as the packet flow from the VM to the physical interface. In OpenStack the Open vSwitch agent takes care of programming the flows in Open vSwitch so the users do not have to deal with this at all. If you wish to learn more about how to program the Open vSwitch you can read more about it at http://openvswitch.org looking at the documentation describing the ovs-ofctl command. Network Namespaces (netns) Network namespaces is a very cool Linux feature can be used for many purposes and is heavily used in OpenStack networking. Network namespaces are isolated containers which can hold a network configuration and is not seen from outside of the namespace. A network namespace can be used to encapsulate specific network functionality or provide a network service in isolation as well as simply help to organize a complicated network setup. Using the Oracle OpenStack Tech Preview we are using the latest Unbreakable Enterprise Kernel R3 (UEK3), this kernel provides a complete support for netns. Let's see how namespaces work through couple of examples to control network namespaces we use the ip netns command: Defining a new namespace: # ip netns add my-ns # ip netns list my-ns As mentioned the namespace is an isolated container, we can perform all the normal actions in the namespace context using the exec command for example running the ifconfig command: # ip netns exec my-ns ifconfig -a lo        Link encap:Local Loopback           LOOPBACK  MTU:16436 Metric:1           RX packets:0 errors:0 dropped:0 overruns:0 frame:0           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0           RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b) We can run every command in the namespace context, this is especially useful for debug using tcpdump command, we can ping or ssh or define iptables all within the namespace. Connecting the namespace to the outside world: There are various ways to connect into a namespaces and between namespaces we will focus on how this is done in OpenStack. OpenStack uses a combination of Open vSwitch and network namespaces. OVS defines the interfaces and then we can add those interfaces to namespace. So first let's add a bridge to OVS: # ovs-vsctl add-br my-bridge Now let's add a port on the OVS and make it internal: # ovs-vsctl add-port my-bridge my-port # ovs-vsctl set Interface my-port type=internal And let's connect it into the namespace: # ip link set my-port netns my-ns Looking inside the namespace: # ip netns exec my-ns ifconfig -a lo        Link encap:Local Loopback           LOOPBACK  MTU:65536 Metric:1           RX packets:0 errors:0 dropped:0 overruns:0 frame:0           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0           RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b) my-port   Link encap:Ethernet HWaddr 22:04:45:E2:85:21           BROADCAST  MTU:1500 Metric:1           RX packets:0 errors:0 dropped:0 overruns:0 frame:0           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0           RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b) Now we can add more ports to the OVS bridge and connect it to other namespaces or other device like physical interfaces. Neutron is using network namespaces to implement network services such as DCHP, routing, gateway, firewall, load balance and more. In the next post we will go into this in further details. Linux Bridge and veth pairs Linux bridge is used to connect the port from OVS to the VM. Every port goes from the OVS bridge to a Linux bridge and from there to the VM. The reason for using regular Linux bridges is for security groups’ enforcement. Security groups are implemented using iptables and iptables can only be applied to Linux bridges and not to OVS bridges. Veth pairs are used extensively throughout the network setup in OpenStack and are also a good tool to debug a network problem. Veth pairs are simply a virtual wire and so veths always come in pairs. Typically one side of the veth pair will connect to a bridge and the other side to another bridge or simply left as a usable interface. In this example we will create some veth pairs, connect them to bridges and test connectivity. This example is using regular Linux server and not an OpenStack node: Creating a veth pair, note that we define names for both ends: # ip link add veth0 type veth peer name veth1 # ifconfig -a . . veth0     Link encap:Ethernet HWaddr 5E:2C:E6:03:D0:17           BROADCAST MULTICAST  MTU:1500 Metric:1           RX packets:0 errors:0 dropped:0 overruns:0 frame:0           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000           RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b) veth1     Link encap:Ethernet HWaddr E6:B6:E2:6D:42:B8           BROADCAST MULTICAST  MTU:1500 Metric:1           RX packets:0 errors:0 dropped:0 overruns:0 frame:0           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000           RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b) . . To make the example more meaningful this we will create the following setup: veth0 => veth1 => br-eth3 => eth3 ======> eth2 on another Linux server br-eth3 – a regular Linux bridge which will be connected to veth1 and eth3 eth3 – a physical interface with no IP on it, connected to a private network eth2 – a physical interface on the remote Linux box connected to the private network and configured with the IP of 50.50.50.1 Once we create the setup we will ping 50.50.50.1 (the remote IP) through veth0 to test that the connection is up: # brctl addbr br-eth3 # brctl addif br-eth3 eth3 # brctl addif br-eth3 veth1 # brctl show bridge name     bridge id               STP enabled     interfaces br-eth3         8000.00505682e7f6       no              eth3                                                         veth1 # ifconfig veth0 50.50.50.50 # ping -I veth0 50.50.50.51 PING 50.50.50.51 (50.50.50.51) from 50.50.50.50 veth0: 56(84) bytes of data. 64 bytes from 50.50.50.51: icmp_seq=1 ttl=64 time=0.454 ms 64 bytes from 50.50.50.51: icmp_seq=2 ttl=64 time=0.298 ms When the naming is not as obvious as the previous example and we don't know who are the paired veth interfaces we can use the ethtool command to figure this out. The ethtool command returns an index we can look up using ip link command, for example: # ethtool -S veth1 NIC statistics: peer_ifindex: 12 # ip link . . 12: veth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000 Summary That’s all for now, we quickly reviewed OVS, network namespaces, Linux bridges and veth pairs. These components are heavily used in the OpenStack network architecture we are exploring and understanding them well will be very useful when reviewing the different use cases. In the next post we will look at how the OpenStack network is laid out connecting the virtual machines to each other and to the external world. @RonenKofman

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• Type classes or implicit parameters? What do you prefer and why? [closed]

  - by Petr Pudlák

  I was playing a bit with Scalaz and I realized that Haskell's type classes are very similar to Scala's implicit parameters. While Haskell passes the methods defined by a type class using hidden dictionaries, Scala allows a similar thing using implicit parameters. For example, in Haskell, one could write: incInside :: (Functor f) => f Int -> f Int incInside = fmap (+ 1) and the same function using Scalaz: import scalaz._; import Scalaz._; def incInside[F[_]](x: F[Int])(implicit fn: Functor[F]): F[Int] = fn.fmap(x, (_:Int) + 1); I wonder: If you could choose (i.e. your favorite language would offer both), what would you pick - implicits or type classes? And what are your pros/cons?

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• The Excel Column Name assigment problem

  - by Peter Larsson

  Here is a generic algorithm to get the Excel column name according to it's position. By changing the @Base parameter, you can do this for any sequence according to same style as Excel. DECLARE @Value INT = 8839,         @Base TINYINT = 26   ;WITH cteSequence(Value, Delta, Quote, Base, Chr) AS (     SELECT  CAST(@Value AS INT) AS Value,             CAST(1 AS INT) AS Delta,             CAST(@Base AS INT) AS Quote,             CAST(@Base AS INT) AS Base,             CHAR(65 +(@Value - 1) % @Base) AS Chr       UNION ALL       SELECT  Value AS Value,             Quote AS Delta,             26 * Quote AS Quote,             Base AS Base,             CHAR(65 +((Value - Delta)/ Quote - 1) % Base) AS Chr     FROM    cteSequence     WHERE   CHAR(65 +((Value - Delta)/ Quote - 1) % Base) <> '@' ) SELECT  CAST(Msg AS VARCHAR(MAX)) FROM    (             SELECT        '' + Chr             FROM        cteSequence             ORDER BY    Delta DESC             FOR XML        PATH('')         ) AS x(Msg)

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• Game Timer In C++

  - by user1870398

  I need to be able to find out how many milliseconds since that last update. Is there any way I can find it out with time rather then a thread that counts like I did below? #include <iostream> #include<windows.h> #include<time.h> #include<process.h> using namespace std; int Timer = 0; int LastTimer = 0; bool End = false; void Update(int Ticks) { } void UpdateTimer() { while (true) { LastTimer = Timer; Timer++; Sleep(1); if (End) break; } } int WINAPI WinMain(HINSTANCE par1, HINSTANCE par2, LPSTR par3, int par4) { _beginthread(UpdateTimer, 0, NULL); while(true) { if (Timer == 1000) Timer = 0; Update(Timer - LastTimer); } }

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• Collision Detection, player correction

  - by DoomStone

  I am having some problems with collision detection, I have 2 types of objects excluding the player. Tiles and what I call MapObjects. The tiles are all 16x16, where the MapObjects can be any size, but in my case they are all 16x16. When my player runs along the mapobjects or tiles, it get verry jaggy. The player is unable to move right, and will get warped forward when moving left. I have found the problem, and that is my collision detection will move the player left/right if colliding the object from the side, and up/down if collision from up/down. Now imagine that my player is sitting on 2 tiles, at (10,12) and (11,12), and the player is mostly standing on the (11,12) tile. The collision detection will first run on then (10,12) tile, it calculates the collision depth, and finds that is is a collision from the side, and therefore move the object to the right. After, it will do the collision detection with (11,12) and it will move the character up. So the player will not fall down, but are unable to move right. And when moving left, the same problem will make the player warp forward. This problem have been bugging me for a few days now, and I just can't find a solution! Here is my code that does the collision detection. public void ApplyObjectCollision(IPhysicsObject obj, List<IComponent> mapObjects, TileMap map) { PhysicsVariables physicsVars = GetPhysicsVariables(); Rectangle bounds = ((IComponent)obj).GetBound(); int leftTile = (int)Math.Floor((float)bounds.Left / map.GetTileSize()); int rightTile = (int)Math.Ceiling(((float)bounds.Right / map.GetTileSize())) - 1; int topTile = (int)Math.Floor((float)bounds.Top / map.GetTileSize()); int bottomTile = (int)Math.Ceiling(((float)bounds.Bottom / map.GetTileSize())) - 1; // Reset flag to search for ground collision. obj.IsOnGround = false; // For each potentially colliding tile, for (int y = topTile; y <= bottomTile; ++y) { for (int x = leftTile; x <= rightTile; ++x) { IComponent tile = map.Get(x, y); if (tile != null) { bounds = HandelCollision(obj, tile, bounds, physicsVars); } } } // Handel collision for all Moving objects foreach (IComponent mo in mapObjects) { if (mo == obj) continue; if (mo.GetBound().Intersects(((IComponent)obj).GetBound())) { bounds = HandelCollision(obj, mo, bounds, physicsVars); } } } private Rectangle HandelCollision(IPhysicsObject obj, IComponent objb, Rectangle bounds, PhysicsVaraibales physicsVars) { // If this tile is collidable, SpriteCollision collision = ((IComponent)objb).GetCollisionType(); if (collision != SpriteCollision.Passable) { // Determine collision depth (with direction) and magnitude. Rectangle tileBounds = ((IComponent)objb).GetBound(); Vector2 depth = bounds.GetIntersectionDepth(tileBounds); if (depth != Vector2.Zero) { float absDepthX = Math.Abs(depth.X); float absDepthY = Math.Abs(depth.Y); // Resolve the collision along the shallow axis. if (absDepthY <= absDepthX || collision == SpriteCollision.Platform) { // If we crossed the top of a tile, we are on the ground. if (obj.PreviousBound.Bottom <= tileBounds.Top) obj.IsOnGround = true; // Ignore platforms, unless we are on the ground. if (collision == SpriteCollision.Impassable || obj.IsOnGround) { // Resolve the collision along the Y axis. ((IComponent)obj).Position = new Vector2(((IComponent)obj).Position.X, ((IComponent)obj).Position.Y + depth.Y); // If we hit something about us, remove all velosity upwards if (depth.Y > 0 && obj.IsJumping) { obj.Velocity = new Vector2(obj.Velocity.X, 0); obj.JumpTime = physicsVars.MaxJumpTime; } // Perform further collisions with the new bounds. return ((IComponent)obj).GetBound(); } } else if (collision == SpriteCollision.Impassable) // Ignore platforms. { // Resolve the collision along the X axis. ((IComponent)obj).Position = new Vector2(((IComponent)obj).Position.X + depth.X, ((IComponent)obj).Position.Y); // Perform further collisions with the new bounds. return ((IComponent)obj).GetBound(); } } } return bounds; } Update: I have uploaded the source code, if you want to look that through. I think that my general approach might be wrong when i am working with small tiles, I have also be unable to find any good information on physics and collision detection in Platform games. http://dl.dropbox.com/u/3181816/Sogaard.Games.SuperMario.rar

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