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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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• 2D vector graphic html5 framework

  - by Yury

  I trying to find html5 game framework by following criteria: 1)Real good performance. 2)Good support of vector graphic( objects which contains canvas elements -line, rec,bezierCurve etc.) 3)Easy port to mobile. Optional- Physics Engine. I found 1)Pixi.js- it looks like real good, but i didn't find any info about "vector objects" support. 2) i found "vector objects" support in paper.js I need something like these: http://paperjs.org/examples/chain/ and http://paperjs.org/examples/path-intersections/. But it looks like paper.js- not so good performance as pixi.js. And it is not game engine. Is there any good framework meets these requirements? P.S. I found similar question here Which free HTML5-based game engine meets these requirements?. But it was a long time ago. A lot of new things were created since 2011.

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• How to get a point to the left/right of a vector

  - by MulletDevil

  I have a position vector of a point in space and a quaternion for it's rotation. What i'm trying to calculate is a point too the left and a point to the right. I have the position and rotation(quaternion) of the red dot. What I want is to get the position of the green dots. I have a float value for the distance I want these points to be. With only the position and rotation is it possible to get a unit direction vector pointing left/right which I can multiply by my float value? Edit: I also know the original direction vector.

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• std::vector::size with glDrawElements crashes?

  - by NoobScratcher

  ( win32 / OpenGL 3.3 / GLSL 330 ) I decided after a long time of trying to do a graphical user interface using just opengl graphics to go back to a gui toolkit and so in the process have had to port alot of my code to win32. But I have a problem with my glDrawElement function. my program compiles and runs fine until it gets to glDrawElements then crashes.. which is rather annoying right. so I was trying to figure out why and I found out its std::vector::size member not returning the correct amount of faces in the unsigned interger vector eg, "vector<unsigned int>faces; " so when I use cout << faces.size() << endl; I got 68 elements???? instead of 24 as you can see here in this .obj file: # Blender v2.61 (sub 0) OBJ File: '' # www.blender.org v 1.000000 -1.000000 -1.000000 v 1.000000 -1.000000 1.000000 v -1.000000 -1.000000 1.000000 v -1.000000 -1.000000 -1.000000 v 1.000000 1.000000 -0.999999 v 0.999999 1.000000 1.000001 v -1.000000 1.000000 1.000000 v -1.000000 1.000000 -1.000000 s off f 1 2 3 4 f 5 8 7 6 f 1 5 6 2 f 2 6 7 3 <--- 24 Faces not 68? f 3 7 8 4 f 5 1 4 8 I'm using a parser I created to get the faces/vertexes in my .obj file: char modelbuffer [20000]; int MAX_BUFF = 20000; unsigned int face[3]; FILE * pfile; pfile = fopen(szFileName, "rw"); while(fgets(modelbuffer, MAX_BUFF, pfile) != NULL) { if('v') { Point p; sscanf(modelbuffer, "v %f %f %f", &p.x, &p.y, &p.z); points.push_back(p); cout << " p.x = " << p.x << " p.y = " << p.y << " p.z = " << p.x << endl; } if('f') { sscanf(modelbuffer, "f %d %d %d %d", &face[0], &face[1], &face[2], &face[3]); cout << "face[0] = " << face[0] << " face[1] = " << face[1] << " face[2] = " << face[2] << " face[3] = " << face[3] << "\n"; faces.push_back(face[0] - 1); faces.push_back(face[1] - 1); faces.push_back(face[2] - 1); faces.push_back(face[3] - 1); cout << face[0] - 1 << face[1] - 1 << face[2] - 1 << face[3] - 1 << endl; } } using this struct to store the x,y,z positions also this vector was used with Point: vector<Point>points; struct Point { float x, y, z; }; If someone could tell me why its not working and how to fix it that would be awesome I also provide a pastebin to the full source code if you want a closer look. http://pastebin.com/gznYLVw7

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• vector rotations for branches of a 3d tree

  - by freefallr

  I'm attempting to create a 3d tree procedurally. I'm hoping that someone can check my vector rotation maths, as I'm a bit confused. I'm using an l-system (a recursive algorithm for generating branches). The trunk of the tree is the root node. It's orientation is aligned to the y axis. In the next iteration of the tree (e.g. the first branches), I might create a branch that is oriented say by +10 degrees in the X axis and a similar amount in the Z axis, relative to the trunk. I know that I should keep a rotation matrix at each branch, so that it can be applied to child branches, along with any modifications to the child branch. My questions then: for the trunk, the rotation matrix - is that just the identity matrix * initial orientation vector ? for the first branch (and subsequent branches) - I'll "inherit" the rotation matrix of the parent branch, and apply x and z rotations to that also. e.g. using glm::normalize; using glm::rotateX; using glm::vec4; using glm::mat4; using glm::rotate; vec4 vYAxis = vec4(0.0f, 1.0f, 0.0f, 0.0f); vec4 vInitial = normalize( rotateX( vYAxis, 10.0f ) ); mat4 mRotation = mat4(1.0); // trunk rotation matrix = identity * initial orientation vector mRotation *= vInitial; // first branch = parent rotation matrix * this branches rotations mRotation *= rotate( 10.0f, 1.0f, 0.0f, 0.0f ); // x rotation mRotation *= rotate( 10.0f, 0.0f, 0.0f, 1.0f ); // z rotation Are my maths and approach correct, or am I completely wrong? Finally, I'm using the glm library with OpenGL / C++ for this. Is the order of x rotation and z rotation important?

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• C++ and SDL Trouble Creating a STL Vector of a Game Object

  - by Jackson Blades

  I am trying to create a Space Invaders clone using C++ and SDL. The problem I am having is in trying to create Waves of Enemies. I am trying to model this by making my Waves a vector of 8 Enemy objects. My Enemy constructor takes two arguments, an x and y offset. My Wave constructor also takes two arguments, an x and y offset. What I am trying to do is have my Wave constructor initialize a vector of Enemies, and have each enemy given a different x offset so that they are spaced out appropriately. Enemy::Enemy(int x, int y) { box.x = x; box.y = y; box.w = ENEMY_WIDTH; box.h = ENEMY_HEIGHT; xVel = ENEMY_WIDTH / 2; } Wave::Wave(int x, int y) { box.x = x; box.y = y; box.w = WAVE_WIDTH; box.y = WAVE_HEIGHT; xVel = (-1)*ENEMY_WIDTH; yVel = 0; std::vector<Enemy> enemyWave; for (int i = 0; i < enemyWave.size(); i++) { Enemy temp(box.x + ((ENEMY_WIDTH + 16) * i), box.y); enemyWave.push_back(temp); } } I guess what I am asking is if there is a cleaner, more elegant way to do this sort of initialization with vectors, or if this is right at all. Any help is greatly appreciated.

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• (R) How can I get the complement of vector y in vector x

  - by gd047

  That's x \ y using mathematical notation. Suppose x <- c(0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,2,1,1,1,3) y <- c(0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,1) How can I get a vector with ALL the values in x that are not in y. i.e the result should be: 2,1,1,3 There is a similar question here. However, none of the answers returns the result that I want.

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• Do I need the 'w' component in my Vector class?

  - by bobobobo

  Assume you're writing matrix code that handles rotation, translation etc for 3d space. Now the transformation matrices have to be 4x4 to fit the translation component in. However, you don't actually need to store a w component in the vector do you? Even in perspective division, you can simply compute and store w outside of the vector, and perspective divide before returning from the method. For example: // post multiply vec2=matrix*vector Vector operator*( const Matrix & a, const Vector& v ) { Vector r ; // do matrix mult r.x = a._11*v.x + a._12*v.y ... real w = a._41*v.x + a._42*v.y ... // perspective divide r /= w ; return r ; } Is there a point in storing w in the Vector class?

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• Vector normalization gives very imprecise results

  - by Kipras

  When I normalize vectors I receive very strange results. The lengths of the normalized vectors range from 1.0 to almost 1.5. The functions are all written by me, but I just can't find a mistake in my algorithm. When I normalize I just divide all components of the vector by the vector's length. public double length(){ return Math.sqrt(x*x + y*y); } public void normalize(){ if(length() > 0){ x /= length(); y /= length(); } } Is this supposed to happen? I mean I can see the length ranging from 0.9 to 1.1 at worst, but this is just overwhelming. Cheers

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• Trouble with SAT style vector projection in C#/XNA

  - by ssb

  Simply put I'm having a hard time working out how to work with XNA's Vector2 types while maintaining spatial considerations. I'm working with separating axis theorem and trying to project vectors onto an arbitrary axis to check if those projections overlap, but the severe lack of XNA-specific help online combined with pseudo code everywhere that omits key parts of the algorithm, googling has left me little help. I'm aware of HOW to project a vector, but the way that I know of doing it involves the two vectors starting from the same point. Particularly here: http://www.metanetsoftware.com/technique/tutorialA.html So let's say I have a simple rectangle, and I store each of its corners in a list of Vector2s. How would I go about projecting that onto an arbitrary axis? The crux of my problem is that taking the dot product of say, a vector2 of (1, 0) and a vector2 of (50, 50) won't get me the dot product I'm looking for.. or will it? Because that (50, 50) won't be the vector of the polygon's vertex but from whatever XNA calculates. It's getting the calculation from the right starting point that's throwing me off. I'm sorry if this is unclear, but my brain is fried from trying to think about this. I need a better understanding of how XNA calculates Vector2s as actual vectors and not just as random points.

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• Glm Vector Transformations [duplicate]

  - by Reanimation

  This question already has an answer here: Car-like Physics - Basic Maths to Simulate Steering 2 answers I have a cube rendered on the screen which represents a car (or similar). Using Projection/Model matrices and Glm I am able to move it back and fourth along the axes and rotate it left or right. I'm having trouble with the vector mathematics to make the cube move forwards no matter which direction it's current orientation is. (ie. if I would like, if it's rotated right 30degrees, when it's move forwards, it travels along the 30degree angle on a new axes). I hope I've explained that correctly. This is what I've managed to do so far in terms of using glm to move the cube: glm::vec3 vel; //velocity vector void renderMovingCube(){ glUseProgram(movingCubeShader.handle()); GLuint matrixLoc4MovingCube = glGetUniformLocation(movingCubeShader.handle(), "ProjectionMatrix"); glUniformMatrix4fv(matrixLoc4MovingCube, 1, GL_FALSE, &ProjectionMatrix[0][0]); glm::mat4 viewMatrixMovingCube; viewMatrixMovingCube = glm::lookAt(camOrigin, camLookingAt, camNormalXYZ); vel.x = cos(rotX); vel.y=sin(rotX); vel*=moveCube; //move cube ModelViewMatrix = glm::translate(viewMatrixMovingCube,globalPos*vel); //bring ground and cube to bottom of screen ModelViewMatrix = glm::translate(ModelViewMatrix, glm::vec3(0,-48,0)); ModelViewMatrix = glm::rotate(ModelViewMatrix, rotX, glm::vec3(0,1,0)); //manually turn glUniformMatrix4fv(glGetUniformLocation(movingCubeShader.handle(), "ModelViewMatrix"), 1, GL_FALSE, &ModelViewMatrix[0][0]); //pass matrix to shader movingCube.render(); //draw glUseProgram(0); } keyboard input: void keyboard() { char BACKWARD = keys['S']; char FORWARD = keys['W']; char ROT_LEFT = keys['A']; char ROT_RIGHT = keys['D']; if (FORWARD) //W - move forwards { globalPos += vel; //globalPos.z -= moveCube; BACKWARD = false; } if (BACKWARD)//S - move backwards { globalPos.z += moveCube; FORWARD = false; } if (ROT_LEFT)//A - turn left { rotX +=0.01f; ROT_LEFT = false; } if (ROT_RIGHT)//D - turn right { rotX -=0.01f; ROT_RIGHT = false; } Where am I going wrong with my vectors? I would like change the direction of the cube (which it does) but then move forwards in that direction.

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• what happens when you copy vector<boost::share_ptr> to another vector

  - by SWKK

  Do we get multiple copies of the pointers yet the data members are still being shared?

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• Rotate a vector by given degrees (errors when value over 90)

  - by Ivan

  I created a function to rotate a vector by a given number of degrees. It seems to work fine when given values in the range -90 to +90. Beyond this, the amount of rotation decreases, i.e., I think objects are rotating the same amount for 80 and 100 degrees. I think this diagram might be a clue to my problem, but I don't quite understand what it's showing. Must I use a different trig function depending on the radians value? The programming examples I've been able to find look similar to mine (not varying the trig functions). Vector2D.prototype.rotate = function(angleDegrees) { var radians = angleDegrees * (Math.PI / 180); var ca = Math.cos(radians); var sa = Math.sin(radians); var rx = this.x*ca - this.y*sa; var ry = this.x*sa + this.y*ca; this.x = rx; this.y = ry; };

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• Smooth vector based jump

  - by Esa

  I started working on Wolfire's mathematics tutorials. I got the jumping working well using a step by step system, where you press a button and the cube moves to the next point on the jumping curve. Then I tried making the jumping happen during a set time period e.g the jump starts and lands within 1.5 seconds. I tried the same system I used for the step by step implementation, but it happens instantly. After some googling I found that Time.deltatime should be used, but I could not figure how. Below is my current jumping code, which makes the jump happen instantly. while (transform.position.y > 0) { modifiedJumperVelocity -= jumperDrag; transform.position += new Vector3(modifiedJumperVelocity.x, modifiedJumperVelocity.y, 0); } Where modifiedJumperVelocity is starting vector minus the jumper drag. JumperDrag is the value that is substracted from the modifiedJumperVelocity during each step of the jump. Below is an image of the jumping curve:

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• Vector.Unproject - Checking if a model intersects a large sprite

  - by Fibericon

  Let's say I have a sprite, drawn like this: spriteBatch.Draw(levelCannons[i].texture, levelCannons[i].position, null, alpha, levelCannons[i].rotation, Vector2.Zero, scale, SpriteEffects.None, 0); Picture levelCannon as being a laser beam that goes across the entire screen. I need to see if my 3d model intersects with the screen space inhabited by the sprite. I managed to dig up Vector.Unproject, but that seems to only be useful when dealing with a single point in 2d space, rather than an area. What can I do in my case?

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• Calculate vector direction

  - by Starkers

  Is the direction angle always measured from the plus x axis? Does a vector in the +,+ quadrant always have a direction between 0 and 90, and in -,+ between 90 and 180 and in -,- between 180 and 270 and in -,+ between 270 and 360 ? Also, how should we calculate the direction using tan? Would that mean nested if statements to find out what quadrant we're in, and then applying the appropriate "work arounds"? E.g. If we were in the -,+ (like in the diagram) would we find the angle from the + axis would be 90 + tan^-1(y/x), the 90 + only used because we're in the -,+ quadrant. Also, that's just a quick solution, may be off, I just want to know if we use nested if statements to get the angle from the + x axis. Finally, should we find the distance in degrees or radians?

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• Calculate initial velocity of a 3d vector-based projectile

  - by Frotty

  Okay, so I got a Projectile with 2 Vectors, position and velocity. I now want to calculate the initial velocity for it in order to reach a specific point on the map. Or actually, how high has the start z-velocity to be (because x and y are probably defined by a speed variable) in order for the projectile to hit the marked position. The projectile is influenced by a constant gravity vector. All calculations are done 32 times per second. I want this, because I don't want to use a parabola function, so the projectile can still be influenced by other sources, simply adding some velocity. I didn't really find anything referring to that topic and would be glad for every helping answer, Thanks.

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• Vector reflect problem

  - by xdevel2000

  I'm testing some vector reflection and I want to check what happens when a ball collides with a paddle. So if I have: Vector2 velocity = new Vector2(-5, 2); position_ball += velocity; if (position_ball.X < 10) { Vector2 v = new Vector2(1,0); // or Vector2.UnitX velocity = Vector2.Reflect(velocity, v); } then, correctly, velocity is (5,2) after Reflect, but if I do: if (position_ball.X < 10) { Vector2 v = new Vector2(1,1); velocity = Vector2.Reflect(velocity, v); } then velocity is (1,8) and not (5, -2) that is the solution of reflection equation R = V - 2 * (V . N) Why is that?

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• Compilation problems with vector<auto_ptr<> >

  - by petersohn

  Consider the following code: #include <iostream> #include <memory> #include <vector> using namespace std; struct A { int a; A(int a_):a(a_) {} }; int main() { vector<auto_ptr<A> > as; for (int i = 0; i < 10; i++) { auto_ptr<A> a(new A(i)); as.push_back(a); } for (vector<auto_ptr<A> >::iterator it = as.begin(); it != as.end(); ++it) cout << (*it)->a << endl; } When trying to compile it, I get the following obscure compiler error from g++: g++ -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/proba.d" -MT"src/proba.d" -o"src/proba.o" "../src/proba.cpp" /usr/include/c++/4.1.2/ext/new_allocator.h: In member function ‘void __gnu_cxx::new_allocator<_Tp>::construct(_Tp*, const _Tp&) [with _Tp = std::auto_ptr<A>]’: /usr/include/c++/4.1.2/bits/stl_vector.h:606: instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = std::auto_ptr<A>, _Alloc = std::allocator<std::auto_ptr<A> >]’ ../src/proba.cpp:19: instantiated from here /usr/include/c++/4.1.2/ext/new_allocator.h:104: error: passing ‘const std::auto_ptr<A>’ as ‘this’ argument of ‘std::auto_ptr<_Tp>::operator std::auto_ptr_ref<_Tp1>() [with _Tp1 = A, _Tp = A]’ discards qualifiers /usr/include/c++/4.1.2/bits/vector.tcc: In member function ‘void std::vector<_Tp, _Alloc>::_M_insert_aux(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, const _Tp&) [with _Tp = std::auto_ptr<A>, _Alloc = std::allocator<std::auto_ptr<A> >]’: /usr/include/c++/4.1.2/bits/stl_vector.h:610: instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = std::auto_ptr<A>, _Alloc = std::allocator<std::auto_ptr<A> >]’ ../src/proba.cpp:19: instantiated from here /usr/include/c++/4.1.2/bits/vector.tcc:256: error: passing ‘const std::auto_ptr<A>’ as ‘this’ argument of ‘std::auto_ptr<_Tp>::operator std::auto_ptr_ref<_Tp1>() [with _Tp1 = A, _Tp = A]’ discards qualifiers /usr/include/c++/4.1.2/bits/stl_construct.h: In function ‘void std::_Construct(_T1*, const _T2&) [with _T1 = std::auto_ptr<A>, _T2 = std::auto_ptr<A>]’: /usr/include/c++/4.1.2/bits/stl_uninitialized.h:86: instantiated from ‘_ForwardIterator std::__uninitialized_copy_aux(_InputIterator, _InputIterator, _ForwardIterator, __false_type) [with _InputIterator = __gnu_cxx::__normal_iterator<std::auto_ptr<A>*, std::vector<std::auto_ptr<A>, std::allocator<std::auto_ptr<A> > > >, _ForwardIterator = __gnu_cxx::__normal_iterator<std::auto_ptr<A>*, std::vector<std::auto_ptr<A>, std::allocator<std::auto_ptr<A> > > >]’ /usr/include/c++/4.1.2/bits/stl_uninitialized.h:113: instantiated from ‘_ForwardIterator std::uninitialized_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = __gnu_cxx::__normal_iterator<std::auto_ptr<A>*, std::vector<std::auto_ptr<A>, std::allocator<std::auto_ptr<A> > > >, _ForwardIterator = __gnu_cxx::__normal_iterator<std::auto_ptr<A>*, std::vector<std::auto_ptr<A>, std::allocator<std::auto_ptr<A> > > >]’ /usr/include/c++/4.1.2/bits/stl_uninitialized.h:254: instantiated from ‘_ForwardIterator std::__uninitialized_copy_a(_InputIterator, _InputIterator, _ForwardIterator, std::allocator<_Tp>) [with _InputIterator = __gnu_cxx::__normal_iterator<std::auto_ptr<A>*, std::vector<std::auto_ptr<A>, std::allocator<std::auto_ptr<A> > > >, _ForwardIterator = __gnu_cxx::__normal_iterator<std::auto_ptr<A>*, std::vector<std::auto_ptr<A>, std::allocator<std::auto_ptr<A> > > >, _Tp = std::auto_ptr<A>]’ /usr/include/c++/4.1.2/bits/vector.tcc:279: instantiated from ‘void std::vector<_Tp, _Alloc>::_M_insert_aux(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, const _Tp&) [with _Tp = std::auto_ptr<A>, _Alloc = std::allocator<std::auto_ptr<A> >]’ /usr/include/c++/4.1.2/bits/stl_vector.h:610: instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = std::auto_ptr<A>, _Alloc = std::allocator<std::auto_ptr<A> >]’ ../src/proba.cpp:19: instantiated from here /usr/include/c++/4.1.2/bits/stl_construct.h:81: error: passing ‘const std::auto_ptr<A>’ as ‘this’ argument of ‘std::auto_ptr<_Tp>::operator std::auto_ptr_ref<_Tp1>() [with _Tp1 = A, _Tp = A]’ discards qualifiers make: *** [src/proba.o] Error 1 It seems to me that there is some kind of problem with consts here. Does this mean that auto_ptr can't be used in vectors?

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• Compilng problems with vector<auto_ptr<> >

  - by petersohn

  Consider the following code: #include <iostream> #include <memory> #include <vector> using namespace std; struct A { int a; A(int a_):a(a_) {} }; int main() { vector<auto_ptr<A> > as; for (int i = 0; i < 10; i++) { auto_ptr<A> a(new A(i)); as.push_back(a); } for (vector<auto_ptr<A> >::iterator it = as.begin(); it != as.end(); ++it) cout << (*it)->a << endl; } When trying to compile it, I get the following obscure compiler error from g++: g++ -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/proba.d" -MT"src/proba.d" -o"src/proba.o" "../src/proba.cpp" /usr/include/c++/4.1.2/ext/new_allocator.h: In member function ‘void __gnu_cxx::new_allocator<_Tp>::construct(_Tp*, const _Tp&) [with _Tp = std::auto_ptr<A>]’: /usr/include/c++/4.1.2/bits/stl_vector.h:606: instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = std::auto_ptr<A>, _Alloc = std::allocator<std::auto_ptr<A> >]’ ../src/proba.cpp:19: instantiated from here /usr/include/c++/4.1.2/ext/new_allocator.h:104: error: passing ‘const std::auto_ptr<A>’ as ‘this’ argument of ‘std::auto_ptr<_Tp>::operator std::auto_ptr_ref<_Tp1>() [with _Tp1 = A, _Tp = A]’ discards qualifiers /usr/include/c++/4.1.2/bits/vector.tcc: In member function ‘void std::vector<_Tp, _Alloc>::_M_insert_aux(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, const _Tp&) [with _Tp = std::auto_ptr<A>, _Alloc = std::allocator<std::auto_ptr<A> >]’: /usr/include/c++/4.1.2/bits/stl_vector.h:610: instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = std::auto_ptr<A>, _Alloc = std::allocator<std::auto_ptr<A> >]’ ../src/proba.cpp:19: instantiated from here /usr/include/c++/4.1.2/bits/vector.tcc:256: error: passing ‘const std::auto_ptr<A>’ as ‘this’ argument of ‘std::auto_ptr<_Tp>::operator std::auto_ptr_ref<_Tp1>() [with _Tp1 = A, _Tp = A]’ discards qualifiers /usr/include/c++/4.1.2/bits/stl_construct.h: In function ‘void std::_Construct(_T1*, const _T2&) [with _T1 = std::auto_ptr<A>, _T2 = std::auto_ptr<A>]’: /usr/include/c++/4.1.2/bits/stl_uninitialized.h:86: instantiated from ‘_ForwardIterator std::__uninitialized_copy_aux(_InputIterator, _InputIterator, _ForwardIterator, __false_type) [with _InputIterator = __gnu_cxx::__normal_iterator<std::auto_ptr<A>*, std::vector<std::auto_ptr<A>, std::allocator<std::auto_ptr<A> > > >, _ForwardIterator = __gnu_cxx::__normal_iterator<std::auto_ptr<A>*, std::vector<std::auto_ptr<A>, std::allocator<std::auto_ptr<A> > > >]’ /usr/include/c++/4.1.2/bits/stl_uninitialized.h:113: instantiated from ‘_ForwardIterator std::uninitialized_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = __gnu_cxx::__normal_iterator<std::auto_ptr<A>*, std::vector<std::auto_ptr<A>, std::allocator<std::auto_ptr<A> > > >, _ForwardIterator = __gnu_cxx::__normal_iterator<std::auto_ptr<A>*, std::vector<std::auto_ptr<A>, std::allocator<std::auto_ptr<A> > > >]’ /usr/include/c++/4.1.2/bits/stl_uninitialized.h:254: instantiated from ‘_ForwardIterator std::__uninitialized_copy_a(_InputIterator, _InputIterator, _ForwardIterator, std::allocator<_Tp>) [with _InputIterator = __gnu_cxx::__normal_iterator<std::auto_ptr<A>*, std::vector<std::auto_ptr<A>, std::allocator<std::auto_ptr<A> > > >, _ForwardIterator = __gnu_cxx::__normal_iterator<std::auto_ptr<A>*, std::vector<std::auto_ptr<A>, std::allocator<std::auto_ptr<A> > > >, _Tp = std::auto_ptr<A>]’ /usr/include/c++/4.1.2/bits/vector.tcc:279: instantiated from ‘void std::vector<_Tp, _Alloc>::_M_insert_aux(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, const _Tp&) [with _Tp = std::auto_ptr<A>, _Alloc = std::allocator<std::auto_ptr<A> >]’ /usr/include/c++/4.1.2/bits/stl_vector.h:610: instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = std::auto_ptr<A>, _Alloc = std::allocator<std::auto_ptr<A> >]’ ../src/proba.cpp:19: instantiated from here /usr/include/c++/4.1.2/bits/stl_construct.h:81: error: passing ‘const std::auto_ptr<A>’ as ‘this’ argument of ‘std::auto_ptr<_Tp>::operator std::auto_ptr_ref<_Tp1>() [with _Tp1 = A, _Tp = A]’ discards qualifiers make: *** [src/proba.o] Error 1 It seems to me that there is some kind of problem with consts here. Does this mean that auto_ptr can't be used in vectors?

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• Referenced vector does not pass through functions

  - by kylepayne

  The referenced vector to functions does not hold the information in memory. Do I have to use pointers? Thanks. #include <iostream> #include <cstdlib> #include <vector> #include <string> using namespace std; void menu(); void addvector(vector<string>& vec); void subvector(vector<string>& vec); void vectorsize(const vector<string>& vec); void printvec(const vector<string>& vec); void printvec_bw(const vector<string>& vec); int main() { vector<string> svector; menu(); return 0; } //functions definitions void menu() { vector<string> svector; int choice = 0; cout << "Thanks for using this program! \n" << "Enter 1 to add a string to the vector \n" << "Enter 2 to remove the last string from the vector \n" << "Enter 3 to print the vector size \n" << "Enter 4 to print the contents of the vector \n" << "Enter 5 ----------------------------------- backwards \n" << "Enter 6 to end the program \n"; cin >> choice; switch(choice) { case 1: addvector(svector); menu(); break; case 2: subvector(svector); menu(); break; case 3: vectorsize(svector); menu(); break; case 4: printvec(svector); menu(); break; case 5: printvec_bw(svector); menu(); break; case 6: exit(1); default: cout << "not a valid choice \n"; // menu is structured so that all other functions are called from it. } } void addvector(vector<string>& vec) { //string line; //int i = 0; //cin.ignore(1, '\n'); //cout << "Enter the string please \n"; //getline(cin, line); vec.push_back("the police man's beard is half-constructed"); } void subvector(vector<string>& vec) { vec.pop_back(); return; } void vectorsize(const vector<string>& vec) { if (vec.empty()) { cout << "vector is empty"; } else { cout << vec.size() << endl; } return; } void printvec(const vector<string>& vec) { for(int i = 0; i < vec.size(); i++) { cout << vec[i] << endl; } return; } void printvec_bw(const vector<string>& vec) { for(int i = vec.size(); i > 0; i--) { cout << vec[i] << endl; } return; }

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• Maps with a nested vector

  - by wawiti

  For some reason the compiler won't let me retrieve the vector of integers from the map that I've created, I want to be able to overwrite this vector with a new vector. The error the compiler gives me is ridiculous. Thanks for your help!! The compiler didn't like this part of my code: line_num = miss_words[word_1]; Error: [Wawiti@localhost Lab2]$ g++ -g -Wall *.cpp -o lab2 main.cpp: In function ‘int main(int, char**)’: main.cpp:156:49: error: no match for ‘operator=’ in ‘miss_words.std::map<_Key, _Tp, _Compare, _Alloc>::operator[]<std::basic_string<char>, std::vector<int>, std::less<std::basic_string<char> >, std::allocator<std::pair<const std::basic_string<char>, std::vector<int> > > >((*(const key_type*)(& word_1))) = line_num.std::vector<_Tp, _Alloc>::push_back<int, std::allocator<int> >((*(const value_type*)(& line)))’ main.cpp:156:49: note: candidate is: In file included from /usr/lib/gcc/x86_64-redhat->linux/4.7.2/../../../../include/c++/4.7.2vector:70:0, from header.h:19, from main.cpp:15: /usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../include/c++/4.7.2/bits/vector.tcc:161:5: note: std::vector<_Tp, _Alloc>& std::vector<_Tp, _Alloc>::operator=(const std::vector<_Tp, _Alloc>&) [with _Tp = int; _Alloc = std::allocator<int>] /usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../include/c++/4.7.2/bits/vector.tcc:161:5: note: no known conversion for argument 1 from ‘void’ to ‘const std::vector<int>&’ CODE: map<string, vector<int> > miss_words; // Creates a map for misspelled words string word_1; // String for word; string sentence; // To store each line; vector<int> line_num; // To store line numbers ifstream file; // Opens file to be spell checked file.open(argv[2]); int line = 1; while(getline(file, sentence)) // Reads in file sentence by sentence { sentence=remove_punct(sentence); // Removes punctuation from sentence stringstream pars_sentence; // Creates stringstream pars_sentence << sentence; // Places sentence in a stringstream while(pars_sentence >> word_1) // Picks apart sentence word by word { if(dictionary.find(word_1)==dictionary.end()) { line_num = miss_words[word_1]; //Compiler doesn't like this miss_words[word_1] = line_num.push_back(line); } } line++; // Increments line marker }

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• Moving sprite from one vector to the other

  - by user2002495

  I'm developing a game where enemy can shoot bullets towards the player. I'm using 2 vector that is normalized later to determine where the bullets will go. Here is the code where enemy shoots: private void UpdateCommonBullet(GameTime gt) { foreach (CommonEnemyBullet ceb in bulletList) { ceb.pos += ceb.direction * 1.5f * (float)gt.ElapsedGameTime.TotalSeconds; if (ceb.pos.Y >= 600) ceb.hasFired = false; } for (int i = 0; i < bulletList.Count; i++) { if (!bulletList[i].hasFired) { bulletList.RemoveAt(i); i--; } } } And here is where i get the direction (in the constructor of the bullet): direction = Global.currentPos - this.pos; direction.Normalize(); Global.currentPos is a Vector2 where currently player is located, and is updated eveytime the player moves. This all works fine except that the bullet won't go to player's location. Instead, it tends goes to the "far right" of the player's position. I think it might be the problem where the bullet (this.pos in the direction) is created (at the position of the enemy). But I found no solution of it, please help me.

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• Vector transform equation explanation

  - by cyberdemon

  I'm trying to understand the maths of moving points in a 3d space by making a game written in C#. I'm looking at this wolfire blog series which explains some basic 3d maths. I've read the first two parts but am stuck on the 3rd. I know it's all really rudimentary stuff but I find Googling for help with equations really hard. The one I'm struggling with is: 0*(0.66,0.75) + 2*(-0.75, 0.66) = (-1.5, 1.3) How can anything multiplied by 0 not be 0? So my question is how does this look in code: x(a,b) + y(c,d) I know it's basic stuff but I just can't see it.

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