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  • vector iterator not dereferencable at runtime on a vector<vector<vector<A*>*>*>

    - by marouanebj
    Hi, I have this destructor that create error at runtime "vector iterator not dereferencable". The gridMatrix is a std::vector<std::vector<std::vector<AtomsCell< Atom<T> * > * > * > * > I added the typename and also the typedef but I still have the error. I will move for this idea of vect of vect* of vect* to use boost::multi_array I think, but still I want to understand were this is wrong. /// @brief destructor ~AtomsGrid(void) { // free all the memory for all the pointers inside gridMatrix (all except the Atom<T>* ) //typedef typename ::value_type value_type; typedef std::vector<AtomsCell< Atom<T>* >*> std_vectorOfAtomsCell; typedef std::vector<std_vectorOfAtomsCell*> std_vectorOfVectorOfAtomsCell; std_vectorOfAtomsCell* vectorOfAtomsCell; std_vectorOfVectorOfAtomsCell* vectorOfVecOfAtomsCell; typename std_vectorOfVectorOfAtomsCell::iterator itSecond; typename std_vectorOfVectorOfAtomsCell::reverse_iterator reverseItSecond; typename std::vector<std_vectorOfVectorOfAtomsCell*>::iterator itFirst; //typename std::vector<AtomsCell< Atom<T>* >*>* vectorOfAtomsCell; //typename std::vector<std::vector<AtomsCell< Atom<T>* >*>*>* vectorOfVecOfAtomsCell; //typename std::vector<std::vector<AtomsCell< Atom<T>* >*>*>::iterator itSecond; //typename std::vector<std::vector<AtomsCell< Atom<T>* >*>*>::reverse_iterator reverseItSecond; //typename std::vector<std::vector<std::vector<AtomsCell< Atom<T>* >*>*>*>::iterator itFirst; for (itFirst = gridMatrix.begin(); itFirst != gridMatrix.end(); ++itFirst) { vectorOfVecOfAtomsCell = (*itFirst); while (!vectorOfVecOfAtomsCell->empty()) { reverseItSecond = vectorOfVecOfAtomsCell->rbegin(); itSecond = vectorOfVecOfAtomsCell->rbegin().base(); vectorOfAtomsCell = (*itSecond); // ERROR during run: "vector iterator not dereferencable" // I think the ERROR is because I need some typedef typename or template ???!!! // the error seems here event at itFirst //fr_Myit_Utils::vectorElementDeleter(*vectorOfAtomsCell); //vectorOfVecOfAtomsCell->pop_back(); } } fr_Myit_Utils::vectorElementDeleter(gridMatrix); } If someone want the full code that create the error I'm happy to give it but I do not think we can attach file in the forum. BUT still its is not very big so if you want it I can copy past it here. Thanks

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  • Calc direction vector based on destination vector and distance from enemy in AS3

    - by Phil
    I'm working on a zombie game in AS3 where I want a character to be able to move away from a zombie depending upon how close the zombie is. The character also has a destination that it's trying to get too on the screen. Ok so I have 2 vectors, one pointing to my destination, and one pointing to the zombie which I then invert to get my "away" vector. I then turn the distance between my character and the zombie into a value between 0 and 1. And then I'm stuck on how to get a resultant vector for my character. How would I use my 0-1 value to calculate how much of the away vector is used and how much of the original destination vector is still left if that makes sense? to end up with 1 direction vector to move my character? So if the zombie is right where my character is, then my direction vector = away vector, and if I'm far away from the zombie than my direction vector = destination vector, but how do I calculate the in-between? Ideally need the answer in AS3.

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  • Transform 3d viewport vector to 2d vector

    - by learning_sam
    I am playing around with 3d transformations and came along an issue. I have a 3d vector already within the viewport and need to transform it to a 2d vector. (let's say my screen is 10x10) Does that just straight works like regualar transformation or is something different here? i.e.: I have the vector a = (2, 1, 0) within the viewport and want the 2d vector. Does that works like this and if yes how do I handle the "0" within the 3rd component?

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  • 3D Vector "End Point" Calculation for procedural Vector Graphics

    - by FrostFlame64
    Alright, So I need some help with some Vector Math. I've developing some game Engines that have Procedural Fractal Generation for Some Graphics, such as using Lindenmayer Systems for generating Trees and Plants. L-Systems, are drawn by using Turtle Graphics, which is a form of Vector graphics. I first created a system to draw in 2D Graphics, which works perfectly fine. But now I want to make a 3D equivalent, and I’ve run into an issue. For my 2D Version, I created a Method for quickly determining the “End Point” of a Vector-like movement. Given a starting point (X, Y), a direction (between 0 and 360 degrees), and a distance, the end point is calculated by these formulas: newX = startX + distance * Sin((PI * direction) / 180) newY = startY + distance * Cos((PI * direction) / 180) Now I need something Similarly Equivalent for performing this Calculation in 3D, But I haven’t been able to Google anything that could show me how to do this. I'm flexible enough to get whatever required information is needed for this method calculation, in any reasonable form (Vector3, Quaternion, ect). To summarize: Given a starting point/vector position in 3D space (X, Y, Z), a Direction in 3D space (Vector3, Quaternion, ect), and a Distance, I need to find the “End Point” in 3D Space. Thank you for your time and help.

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  • Understanding math used to determine if vector is clockwise / counterclockwise from your vector

    - by MTLPhil
    I'm reading Programming Game AI by Example by Mat Buckland. In the Math & Physics primer chapter there's a listing of the declaration of a class used to represent 2D vectors. This class contains a method called Sign. It's implementation is as follows //------------------------ Sign ------------------------------------------ // // returns positive if v2 is clockwise of this vector, // minus if anticlockwise (Y axis pointing down, X axis to right) //------------------------------------------------------------------------ enum {clockwise = 1, anticlockwise = -1}; inline int Vector2D::Sign(const Vector2D& v2)const { if (y*v2.x > x*v2.y) { return anticlockwise; } else { return clockwise; } } Can someone explain the vector rules that make this hold true? What do the values of y*v2.x and x*v2.y that are being compared actually represent? I'd like to have a solid understanding of why this works rather than just accepting that it does without figuring it out. I feel like it's something really obvious that I'm just not catching on to. Thanks for your help.

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  • Adding Functions to an Implementation of Vector

    - by Meursault
    I have this implementation of vector that I've been working on for a few days using examples from a textbook: #include <iostream> #include <string> #include <cassert> #include <algorithm> #include <cstring> // Vector.h using namespace std; template <class T> class Vector { public: typedef T * iterator; Vector(); Vector(unsigned int size); Vector(unsigned int size, const T & initial); Vector(const Vector<T> & v); // copy constructor ~Vector(); unsigned int capacity() const; // return capacity of vector (in elements) unsigned int size() const; // return the number of elements in the vector bool empty() const; iterator begin(); // return an iterator pointing to the first element iterator end(); // return an iterator pointing to one past the last element T & front(); // return a reference to the first element T & back(); // return a reference to the last element void push_back(const T & value); // add a new element void pop_back(); // remove the last element void reserve(unsigned int capacity); // adjust capacity void resize(unsigned int size); // adjust size void erase(unsigned int size); // deletes an element from the vector T & operator[](unsigned int index); // return reference to numbered element Vector<T> & operator=(const Vector<T> &); private: unsigned int my_size; unsigned int my_capacity; T * buffer; }; template<class T>// Vector<T>::Vector() { my_capacity = 0; my_size = 0; buffer = 0; } template<class T> Vector<T>::Vector(const Vector<T> & v) { my_size = v.my_size; my_capacity = v.my_capacity; buffer = new T[my_size]; for (int i = 0; i < my_size; i++) buffer[i] = v.buffer[i]; } template<class T>// Vector<T>::Vector(unsigned int size) { my_capacity = size; my_size = size; buffer = new T[size]; } template<class T>// Vector<T>::Vector(unsigned int size, const T & initial) { my_size = size; //added = size my_capacity = size; buffer = new T [size]; for (int i = 0; i < size; i++) buffer[i] = initial; } template<class T>// Vector<T> & Vector<T>::operator = (const Vector<T> & v) { delete[ ] buffer; my_size = v.my_size; my_capacity = v.my_capacity; buffer = new T [my_size]; for (int i = 0; i < my_size; i++) buffer[i] = v.buffer[i]; return *this; } template<class T>// typename Vector<T>::iterator Vector<T>::begin() { return buffer; } template<class T>// typename Vector<T>::iterator Vector<T>::end() { return buffer + size(); } template<class T>// T& Vector<T>::Vector<T>::front() { return buffer[0]; } template<class T>// T& Vector<T>::Vector<T>::back() { return buffer[size - 1]; } template<class T> void Vector<T>::push_back(const T & v) { if (my_size >= my_capacity) reserve(my_capacity +5); buffer [my_size++] = v; } template<class T>// void Vector<T>::pop_back() { my_size--; } template<class T>// void Vector<T>::reserve(unsigned int capacity) { if(buffer == 0) { my_size = 0; my_capacity = 0; } if (capacity <= my_capacity) return; T * new_buffer = new T [capacity]; assert(new_buffer); copy (buffer, buffer + my_size, new_buffer); my_capacity = capacity; delete[] buffer; buffer = new_buffer; } template<class T>// unsigned int Vector<T>::size()const { return my_size; } template<class T>// void Vector<T>::resize(unsigned int size) { reserve(size); my_size = size; } template<class T>// T& Vector<T>::operator[](unsigned int index) { return buffer[index]; } template<class T>// unsigned int Vector<T>::capacity()const { return my_capacity; } template<class T>// Vector<T>::~Vector() { delete[]buffer; } template<class T> void Vector<T>::erase(unsigned int size) { } int main() { Vector<int> v; v.reserve(2); assert(v.capacity() == 2); Vector<string> v1(2); assert(v1.capacity() == 2); assert(v1.size() == 2); assert(v1[0] == ""); assert(v1[1] == ""); v1[0] = "hi"; assert(v1[0] == "hi"); Vector<int> v2(2, 7); assert(v2[1] == 7); Vector<int> v10(v2); assert(v10[1] == 7); Vector<string> v3(2, "hello"); assert(v3.size() == 2); assert(v3.capacity() == 2); assert(v3[0] == "hello"); assert(v3[1] == "hello"); v3.resize(1); assert(v3.size() == 1); assert(v3[0] == "hello"); Vector<string> v4 = v3; assert(v4.size() == 1); assert(v4[0] == v3[0]); v3[0] = "test"; assert(v4[0] != v3[0]); assert(v4[0] == "hello"); v3.pop_back(); assert(v3.size() == 0); Vector<int> v5(7, 9); Vector<int>::iterator it = v5.begin(); while (it != v5.end()) { assert(*it == 9); ++it; } Vector<int> v6; v6.push_back(100); assert(v6.size() == 1); assert(v6[0] == 100); v6.push_back(101); assert(v6.size() == 2); assert(v6[0] == 100); v6.push_back(101); cout << "SUCCESS\n"; } So far it works pretty well, but I want to add a couple of functions to it that I can't find examples for, a SWAP function that would look at two elements of the vector and switch their values and and an ERASE function that would delete a specific value or range of values in the vector. How should I begin implementing the two extra functions?

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  • Making only the outer vector in vector<vector<int>> fixed

    - by Dennis Ritchie
    I want to create a vector<vector<int>> where the outer vector is fixed (always containing the same vectors), but the inner vectors can be changed. For example: int n = 2; //decided at runtime assert(n>0); vector<vector<int>> outer(n); //outer vector contains n empty vectors outer.push_back(vector<int>()); //modifying outer vector - this should be error auto outer_it = outer.begin(); (*outer_it).push_back(3); //modifying inner vector. should work (which it does). I tried doing simply const vector<vector<int>>, but that makes even the inner vectors const. Is my only option to create my own custom FixedVectors class, or are there better ways out there to do this?

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  • Rotate a vector relative to itself

    - by Paul Manta
    I have a plane defined by transform.forward and transform.right, with 0 degrees corresponding to the forward vector and positive 90 degrees to the right vector. How can I create a third vector rotated in this plane. A rotation of 0 degrees would mean the vector is identical to transform.forward, a rotation of 30 degrees would mean it forms a 30 degree angle with the forward vector. In other words, I want to rotate the forward vector relative to itself, in the plane it defines with the right vector.

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  • Raycasting tutorial / vector math question

    - by mattboy
    I'm checking out this nice raycasting tutorial at http://lodev.org/cgtutor/raycasting.html and have a probably very simple math question. In the DDA algorithm I'm having trouble understanding the calcuation of the deltaDistX and deltaDistY variables, which are the distances that the ray has to travel from 1 x-side to the next x-side, or from 1 y-side to the next y-side, in the square grid that makes up the world map (see below screenshot). In the tutorial they are calculated as follows, but without much explanation: //length of ray from one x or y-side to next x or y-side double deltaDistX = sqrt(1 + (rayDirY * rayDirY) / (rayDirX * rayDirX)); double deltaDistY = sqrt(1 + (rayDirX * rayDirX) / (rayDirY * rayDirY)); rayDirY and rayDirX are the direction of a ray that has been cast. How do you get these formulas? It looks like pythagorean theorem is part of it, but somehow there's division involved here. Can anyone clue me in as to what mathematical knowledge I'm missing here, or "prove" the formula by showing how it's derived?

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  • vector<vector<largeObject>> vs. vector<vector<largeObject>*> in c++

    - by Leif Andersen
    Obviously it will vary depending on the compiler you use, but I'm curious as to the performance issues when doing vector<vector<largeObject>> vs. vector<vector<largeObject>*>, especially in c++. In specific: let's say that you have the outer vector full, and you want to start inserting elements into first inner vector. How will that be stored in memory if the outer vector is just storing pointers, as apposed to storing the whole inner vector. Will the whole outer vector have to be moved to gain more space, or will the inner vector be moved (assuming that space wasn't pre-allocated), causing problems with the outer vector? Thank you

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  • Private member vector of vector dynamic memory allocation

    - by Geoffroy
    Hello, I'm new to C++ (I learned programming with Fortran), and I would like to allocate dynamically the memory for a multidimensional table. This table is a private member variable : class theclass{ public: void setdim(void); private: std::vector < std::vector <int> > thetable; } I would like to set the dimension of thetable with the function setdim(). void theclass::setdim(void){ this->thetable.assign(1000,std::vector <int> (2000)); } I have no problem compiling this program, but as I execute it, I've got a segmentation fault. The strange thing for me is that this piece (see under) of code does exactly what I want, except that it doesn't uses the private member variable of my class : std::vector < std::vector < int > > thetable; thetable.assign(1000,std::vector <int> (2000)); By the way, I have no trouble if thetable is a 1D vector. In theclass : std::vector < int > thetable; and if in setdim : this->thetable.assign(1000,2); So my question is : why is there such a difference with "assign" between thetable and this-thetable for a 2D vector? And how should I do to do what I want? Thank-you for your help, Best regards, -- Geoffroy

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  • Pushing a vector into an vector

    - by Sunil
    I have a 2d vector typedef vector <double> record_t; typedef vector <record_t> data_t; data_t data; So my 2d vector is data here. It has elements like say, 1 1 1 1 1 2 2 2 2 2 3 3 3 3 3 4 4 4 4 4 5 5 5 5 5 Now I want to insert these elements into another 2d vector std::vector< vector<double> > window; So what I did was to create an iterator for traversing through the rows of data and pushing it into windowlike std::vector< std::vector<double> >::iterator data_it; for (data_it = data.begin() ; data_it != data.end() ; ++data_it) window.push_back ( *data_it ); Can anybody tell me where I'm wrong or suggest a way to do this ? Thanks

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  • Pushing a vector into an vector

    - by Sunil
    I have a 2d vector typedef vector <double> record_t; typedef vector <record_t> data_t; data_t data; So my 2d vector is data here. It has elements like say, 1 1 1 1 1 2 2 2 2 2 3 3 3 3 3 4 4 4 4 4 5 5 5 5 5 Now I want to insert these elements into another 2d vector std::vector< vector<double> > window; So what I did was to create an iterator for traversing through the rows of data and pushing it into window like std::vector< std::vector<double> >::iterator data_it; for (data_it = data.begin() ; data_it != data.end() ; ++data_it){ window.push_back ( *data_it ); // Do something else } Can anybody tell me where I'm wrong or suggest a way to do this ? BTW I want to push it just element by element because I want to be able to do something else inside the loop too. i.e. I want to check for a condition and increment the value of the iterator inside. for example, if a condition satisfies then I'll do data_it+=3 or something like that inside the loop. Thanks P.S. I asked this question last night and didn't get any response and that's why I'm posting it again.

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  • Circle collision detection and Vector math: HELP?

    - by Griffin
    Hey so i'm currently going through the wildbunny blog to learn about collision detection, but i'm a bit confused on how the vectors he's talking about come into play QUOTED BLOG: 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. Ok so i understand that p is the distance each circle is penetrating each other, but i don't get what exactly N and P is. 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||) Whats 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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  • C++: Appending a vector to a vector

    - by sub
    Assuming I have 2 STL vectors: vector<int> a; vector<int> b; Let's also say the both have around 30 elements. How do I add the vector b to the end of vector a? The dirty way would be iterating through b and adding each element via push_back, though I wouldn't like to do that!

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  • How to use a "vector of vector" ?

    - by Mike Dooley
    Hi! I allready searched on the web for it but I didn't get satisfying results. I want to create something like vector< vector<int*> > test_vector; How do i fill this vector of vector? How to acces it's members? Maybe someone knows some nice tutorials on the web? kind regards mikey

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  • c++ vector.push_back error: request for member 'push_back'..., which is of non-class type 'vector(ch

    - by Ziplin
    I'm using Cygwin with GCC, and ultimately I want to read in a file of characters into a vector of characters, and using this code #include <fstream> #include <vector> #include <stdlib.h> using namespace std; int main (int argc, char *argv[] ) { vector<char> string1(); string1.push_back('a'); return 0; } generates this compile time error: main.cpp: In function int main(int, char**)': main.cpp:46: error: request for memberpush_back' in string1', which is of non -class typestd::vector ()()' I tried this with a vector of ints and strings as well and they had the same problem.

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  • Eculidean space and vector magnitude

    - by Starkers
    Below we have distances from the origin calculated in two different ways, giving the Euclidean distance, the Manhattan distance and the Chebyshev distance. Euclidean distance is what we use to calculate the magnitude of vectors in 2D/3D games, and that makes sense to me: Let's say we have a vector that gives us the range a spaceship with limited fuel can travel. If we calculated this with Manhattan metric, our ship could travel a distance of X if it were travelling horizontally or vertically, however the second it attempted to travel diagonally it could only tavel X/2! So like I say, Euclidean distance does make sense. However, I still don't quite get how we calculate 'real' distances from the vector's magnitude. Here are two points, purple at (2,2) and green at (3,3). We can take two points away from each other to derive a vector. Let's create a vector to describe the magnitude and direction of purple from green: |d| = purple - green |d| = (purple.x, purple.y) - (green.x, green.y) |d| = (2, 2) - (3, 3) |d| = <-1,-1> Let's derive the magnitude of the vector via Pythagoras to get a Euclidean measurement: euc_magnitude = sqrt((x*x)+(y*y)) euc_magnitude = sqrt((-1*-1)+(-1*-1)) euc_magnitude = sqrt((1)+(1)) euc_magnitude = sqrt(2) euc_magnitude = 1.41 Now, if the answer had been 1, that would make sense to me, because 1 unit (in the direction described by the vector) from the green is bang on the purple. But it's not. It's 1.41. 1.41 units is the direction described, to me at least, makes us overshoot the purple by almost half a unit: So what do we do to the magnitude to allow us to calculate real distances on our point graph? Worth noting I'm a beginner just working my way through theory. Haven't programmed a game in my life!

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  • map<string, vector<string>> reassignment of vector value

    - by user2950936
    I am trying to write a program that takes lines from an input file, sorts the lines into 'signatures' for the purpose of combining all words that are anagrams of each other. I have to use a map, storing the 'signatures' as the keys and storing all words that match those signatures into a vector of strings. Afterwards I must print all words that are anagrams of each other on the same line. Here is what I have so far: #include <iostream> #include <string> #include <algorithm> #include <map> #include <fstream> using namespace std; string signature(const string&); void printMap(const map<string, vector<string>>&); int main(){ string w1,sig1; vector<string> data; map<string, vector<string>> anagrams; map<string, vector<string>>::iterator it; ifstream myfile; myfile.open("words.txt"); while(getline(myfile, w1)) { sig1=signature(w1); anagrams[sig1]=data.push_back(w1); //to my understanding this should always work, } //either by inserting a new element/key or //by pushing back the new word into the vector<string> data //variable at index sig1, being told that the assignment operator //cannot be used in this way with these data types myfile.close(); printMap(anagrams); return 0; } string signature(const string& w) { string sig; sig=sort(w.begin(), w.end()); return sig; } void printMap(const map& m) { for(string s : m) { for(int i=0;i<m->second.size();i++) cout << m->second.at(); cout << endl; } } The first explanation is working, didn't know it was that simple! However now my print function is giving me: prob2.cc: In function âvoid printMap(const std::map<std::basic_string<char>, std::vector<std::basic_string<char> > >&)â: prob2.cc:43:36: error: cannot bind âstd::basic_ostream<char>::__ostream_type {aka std::basic_ostream<char>}â lvalue to âstd::basic_ostream<char>&&â In file included from /opt/centos/devtoolset-1.1/root/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../include/c++/4.7.2/iostream:40:0, Tried many variations and they always complain about binding void printMap(const map<string, vector<string>> &mymap) { for(auto &c : mymap) cout << c.first << endl << c.second << endl; }

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  • Accessing a vector<vector<int>> as a flat array

    - by user1762276
    For this array: vector<vector<int> > v; v.push_back(vector<int>(0)); v.back().push_back(1); v.back().push_back(2); v.back().push_back(3); v.back().push_back(4); I can output {1, 2, 3, 4} easily enough: cout << v[0][0] << endl; cout << v[0][1] << endl; cout << v[0][2] << endl; cout << v[0][3] << endl; To access it as a flat array I can do this: int* z = (int*)&v[0].front(); cout << z[0] << endl; cout << z[1] << endl; cout << z[2] << endl; cout << z[3] << endl; Now, how do I access the multidimensional vector as a flat multidimensional array? I cannot use the same format as accessing a single-dimensional vector: // This does not work (outputs garbage) int** n = (int**)&v.front(); cout << n[0][0] << endl; cout << n[0][1] << endl; cout << n[0][2] << endl; cout << n[0][3] << endl; The workaround I've found is to do this: int** n = new int* [v.size()]; for (size_t i = 0; i < v.size(); i++) { n[i] = &v.at(i).front(); } cout << n[0][0] << endl; cout << n[0][1] << endl; cout << n[0][2] << endl; cout << n[0][3] << endl; Is there a way to access the entire multidimensional vector like a flat c-style array without having to dynamically allocate each dimension above the data before accessing it? Speed is not critical in the implementation and clarity for maintenance is paramount. A multidimensional vector is just fine for storing the data. However, I want to also expose the data as a flat c-style array in the SDK so that it can be easily accessible by other languages. This means that exposing the vectors as an STL object is a no go. The solution I came up with works fine for my needs as I only evaluate the array once at the very end of processing to "flatten" it. However, is there a better way to go about this? Or am I already doing it the best way I possibly can without re-implementing my own data structure (overkill since my flatten code is only a few lines). Thank you for your advice, friends!

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  • Finding closest object to a location within a specific perpendicular distance to direction vector

    - by Sniper
    I have a location and a direction vector indicating facing, I want to find the closest object to that location that is within some tolerance distance (perpendicular distance) to the ray formed by the location and direction vector. Basically I want to get the object that is being aimed at. I have thought about finding all objects within a box and then finding the closest object to my vector from them results, but I am sure that there is a more efficient way. The Z axis is optional, the objects are most likely within a few meters of the search vector.

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  • Collision: Vector class (java)

    - by user8363
    When handling collision detection / response and you need a Vector class, do you need to create that class yourself or is there a java class you can use? A vector class should have methods like: subtract(Vector v), normalize(), dotProduct(Vector v), ... At the moment it seems logical to use classes like java.awt.Rectangle and java.awt.Polygon to calculate collisions. Would I be right to use these classes for this purpose? My question is not about how to implement collision detection, I know how that works. However I'm wondering what would be a correct and clean way to implement it in java since I'm fairly new to the language and to application development in general.

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  • Accelerated C++, problem 5-6 (copying values from inside a vector to the front)

    - by Darel
    Hello, I'm working through the exercises in Accelerated C++ and I'm stuck on question 5-6. Here's the problem description: (somewhat abbreviated, I've removed extraneous info.) 5-6. Write the extract_fails function so that it copies the records for the passing students to the beginning of students, and then uses the resize function to remove the extra elements from the end of students. (students is a vector of student structures. student structures contain an individual student's name and grades.) More specifically, I'm having trouble getting the vector.insert function to properly copy the passing student structures to the start of the vector students. Here's the extract_fails function as I have it so far (note it doesn't resize the vector yet, as directed by the problem description; that should be trivial once I get past my current issue.) // Extract the students who failed from the "students" vector. void extract_fails(vector<Student_info>& students) { typedef vector<Student_info>::size_type str_sz; typedef vector<Student_info>::iterator iter; iter it = students.begin(); str_sz i = 0, count = 0; while (it != students.end()) { // fgrade tests wether or not the student failed if (!fgrade(*it)) { // if student passed, copy to front of vector students.insert(students.begin(), it, it); // tracks of the number of passing students(so we can properly resize the array) count++; } cout << it->name << endl; // output to verify that each student is iterated to it++; } } The code compiles and runs, but the students vector isn't adding any student structures to its front. My program's output displays that the students vector is unchanged. Here's my complete source code, followed by a sample input file (I redirect input from the console by typing " < grades" after the compiled program name at the command prompt.) #include <iostream> #include <string> #include <algorithm> // to get the declaration of `sort' #include <stdexcept> // to get the declaration of `domain_error' #include <vector> // to get the declaration of `vector' //driver program for grade partitioning examples using std::cin; using std::cout; using std::endl; using std::string; using std::domain_error; using std::sort; using std::vector; using std::max; using std::istream; struct Student_info { std::string name; double midterm, final; std::vector<double> homework; }; bool compare(const Student_info&, const Student_info&); std::istream& read(std::istream&, Student_info&); std::istream& read_hw(std::istream&, std::vector<double>&); double median(std::vector<double>); double grade(double, double, double); double grade(double, double, const std::vector<double>&); double grade(const Student_info&); bool fgrade(const Student_info&); void extract_fails(vector<Student_info>& v); int main() { vector<Student_info> vs; Student_info s; string::size_type maxlen = 0; while (read(cin, s)) { maxlen = max(maxlen, s.name.size()); vs.push_back(s); } sort(vs.begin(), vs.end(), compare); extract_fails(vs); // display the new, modified vector - it should be larger than // the input vector, due to some student structures being // added to the front of the vector. cout << "count: " << vs.size() << endl << endl; vector<Student_info>::iterator it = vs.begin(); while (it != vs.end()) cout << it++->name << endl; return 0; } // Extract the students who failed from the "students" vector. void extract_fails(vector<Student_info>& students) { typedef vector<Student_info>::size_type str_sz; typedef vector<Student_info>::iterator iter; iter it = students.begin(); str_sz i = 0, count = 0; while (it != students.end()) { // fgrade tests wether or not the student failed if (!fgrade(*it)) { // if student passed, copy to front of vector students.insert(students.begin(), it, it); // tracks of the number of passing students(so we can properly resize the array) count++; } cout << it->name << endl; // output to verify that each student is iterated to it++; } } bool compare(const Student_info& x, const Student_info& y) { return x.name < y.name; } istream& read(istream& is, Student_info& s) { // read and store the student's name and midterm and final exam grades is >> s.name >> s.midterm >> s.final; read_hw(is, s.homework); // read and store all the student's homework grades return is; } // read homework grades from an input stream into a `vector<double>' istream& read_hw(istream& in, vector<double>& hw) { if (in) { // get rid of previous contents hw.clear(); // read homework grades double x; while (in >> x) hw.push_back(x); // clear the stream so that input will work for the next student in.clear(); } return in; } // compute the median of a `vector<double>' // note that calling this function copies the entire argument `vector' double median(vector<double> vec) { typedef vector<double>::size_type vec_sz; vec_sz size = vec.size(); if (size == 0) throw domain_error("median of an empty vector"); sort(vec.begin(), vec.end()); vec_sz mid = size/2; return size % 2 == 0 ? (vec[mid] + vec[mid-1]) / 2 : vec[mid]; } // compute a student's overall grade from midterm and final exam grades and homework grade double grade(double midterm, double final, double homework) { return 0.2 * midterm + 0.4 * final + 0.4 * homework; } // compute a student's overall grade from midterm and final exam grades // and vector of homework grades. // this function does not copy its argument, because `median' does so for us. double grade(double midterm, double final, const vector<double>& hw) { if (hw.size() == 0) throw domain_error("student has done no homework"); return grade(midterm, final, median(hw)); } double grade(const Student_info& s) { return grade(s.midterm, s.final, s.homework); } // predicate to determine whether a student failed bool fgrade(const Student_info& s) { return grade(s) < 60; } Sample input file: Moo 100 100 100 100 100 100 100 100 Fail1 45 55 65 80 90 70 65 60 Moore 75 85 77 59 0 85 75 89 Norman 57 78 73 66 78 70 88 89 Olson 89 86 70 90 55 73 80 84 Peerson 47 70 82 73 50 87 73 71 Baker 67 72 73 40 0 78 55 70 Davis 77 70 82 65 70 77 83 81 Edwards 77 72 73 80 90 93 75 90 Fail2 55 55 65 50 55 60 65 60 Thanks to anyone who takes the time to look at this!

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  • Vector with Constant-Time Remove - still a Vector?

    - by Darrel Hoffman
    One of the drawbacks of most common implementations of the Vector class (or ArrayList, etc. Basically any array-backed expandable list class) is that their remove() operation generally operates in linear time - if you remove an element, you must shift all elements after it one space back to keep the data contiguous. But what if you're using a Vector just to be a list-of-things, where the order of the things is irrelevant? In this case removal can be accomplished in a few simple steps: Swap element to be removed with the last element in the array Reduce size field by 1. (No need to re-allocate the array, as the deleted item is now beyond the size field and thus not "in" the list any more. The next add() will just overwrite it.) (optional) Delete last element to free up its memory. (Not needed in garbage-collected languages.) This is clearly now a constant-time operation, since only performs a single swap regardless of size. The downside is of course that it changes the order of the data, but if you don't care about the order, that's not a problem. Could this still be called a Vector? Or is it something different? It has some things in common with "Set" classes in that the order is irrelevant, but unlike a Set it can store duplicate values. (Also most Set classes I know of are backed by a tree or hash map rather than an array.) It also bears some similarity to Heap classes, although without the log(N) percolate steps since we don't care about the order.

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  • How to shift a vector based on the rotation of another vector?

    - by bpierre
    I’m learning 2D programming, so excuse my approximations, and please, don’t hesitate to correct me. I am just trying to fire a bullet from a player. I’m using HTML canvas (top left origin). Here is a representation of my problem: The black vector represent the position of the player (the grey square). The green vector represent its direction. The red disc represents the target. The red vector represents the direction of a bullet, which will move in the direction of the target (red and dotted line). The blue cross represents the point from where I really want to fire the bullet (and the blue and dotted line represents its movement). This is how I draw the player (this is the player object. Position, direction and dimensions are 2D vectors): ctx.save(); ctx.translate(this.position.x, this.position.y); ctx.rotate(this.direction.getAngle()); ctx.drawImage(this.image, Math.round(-this.dimensions.x/2), Math.round(-this.dimensions.y/2), this.dimensions.x, this.dimensions.y); ctx.restore(); This is how I instanciate a new bullet: var bulletPosition = playerPosition.clone(); // Copy of the player position var bulletDirection = Vector2D.substract(targetPosition, playerPosition).normalize(); // Difference between the player and the target, normalized new Bullet(bulletPosition, bulletDirection); This is how I move the bullet (this is the bullet object): var speed = 5; this.position.add(Vector2D.multiply(this.direction, speed)); And this is how I draw the bullet (this is the bullet object): ctx.save(); ctx.translate(this.position.x, this.position.y); ctx.rotate(this.direction.getAngle()); ctx.fillRect(0, 0, 3, 3); ctx.restore(); How can I change the direction and position vectors of the bullet to ensure it is on the blue dotted line? I think I should represent the shift with a vector, but I can’t see how to use it.

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