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  • Do I need a Point and a Vector object? Or just using a Vector object to represent a Point is ok?

    - by JCM
    Structuring the components of an engine that I am developing along with a friend (learning purposes), I came to this doubt. Initially we had a Point constructor, like the following: var Point = function( x, y ) { this.x = x; this.y = y; }; But them we started to add some Vector math to it, and them decided to rename it to Vector2d. But now, some methods are a bit confusing (at least in my opinion), such as the following, which is used to make a line: //before the renaming of Point to Vector2, the parameters were startingPoint and endingPoint Geometry.Line = function( startingVector, endingVector ) { //... }; I should make a specific constructor for the Point object, or there are no problems in defining a point as a vector? I know a vector have magnitude and direction, but I see so many people using a vector to just represent the position of an object.

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  • Adding 2D vector movement with rotation applied

    - by Michael Zehnich
    I am trying to apply a slight sine wave movement to objects that float around the screen to make them a little more interesting. I would like to apply this to the objects so that they oscillate from side to side, not front to back (so the oscillation does not affect their forward velocity). After reading various threads and tutorials, I have come to the conclusion that I need to create and add vectors, but I simply cannot come up with a solution that works. This is where I'm at right now, in the object's update method (updated based on comments): Vector2 oldPosition = new Vector2(spritePos.X, spritePos.Y); //note: newPosition is initially set in the constructor to spritePos.x/y Vector2 direction = newPosition - oldPosition; Vector2 perpendicular = new Vector2(direction.Y, -direction.X); perpendicular.Normalize(); sinePosAng += 0.1f; perpendicular.X += 2.5f * (float)Math.Sin(sinePosAng); spritePos.X += velocity * (float)Math.Cos(radians); spritePos.Y += velocity * (float)Math.Sin(radians); spritePos += perpendicular; newPosition = spritePos;

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  • Rotate a vector

    - by marc wellman
    I want my first-person camera to smoothly change its viewing direction from direction d1 to direction d2. The latter direction is indicated by a target position t2. So far I have implemented a rotation that works fine but the speed of the rotation slows down the closer the current direction gets to the desired one. This is what I want to avoid. Here are the two very simple methods I have written so far: // this method initiates the direction change and sets the parameter public void LookAt(Vector3 target) { _desiredDirection = target - _cameraPosition; _desiredDirection.Normalize(); _rotation = new Matrix(); _rotationAxis = Vector3.Cross(Direction, _desiredDirection); _isLooking = true; } // this method gets execute by the Update()-method if _isLooking flag is up. private void _lookingAt() { dist = Vector3.Distance(Direction, _desiredDirection); // check whether the current direction has reached the desired one. if (dist >= 0.00001f) { _rotationAxis = Vector3.Cross(Direction, _desiredDirection); _rotation = Matrix.CreateFromAxisAngle(_rotationAxis, MathHelper.ToRadians(1)); Direction = Vector3.TransformNormal(Direction, _rotation); } else { _onDirectionReached(); _isLooking = false; } } Again, rotation works fine; camera reaches its desired direction. But the speed is not equal over the course of movement - it slows down. How to achieve a rotation with constant speed ?

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  • Haskell Linear Algebra Matrix Library for Arbitrary Element Types

    - by Johannes Weiß
    I'm looking for a Haskell linear algebra library that has the following features: Matrix multiplication Matrix addition Matrix transposition Rank calculation Matrix inversion is a plus and has the following properties: arbitrary element (scalar) types (in particular element types that are not Storable instances). My elements are an instance of Num, additionally the multiplicative inverse can be calculated. The elements mathematically form a finite field (??2256). That should be enough to implement the features mentioned above. arbitrary matrix sizes (I'll probably need something like 100x100, but the matrix sizes will depend on the user's input so it should not be limited by anything else but the memory or the computational power available) as fast as possible, but I'm aware that a library for arbitrary elements will probably not perform like a C/Fortran library that does the work (interfaced via FFI) because of the indirection of arbitrary (non Int, Double or similar) types. At least one pointer gets dereferenced when an element is touched (written in Haskell, this is not a real requirement for me, but since my elements are no Storable instances the library has to be written in Haskell) I already tried very hard and evaluated everything that looked promising (most of the libraries on Hackage directly state that they wont work for me). In particular I wrote test code using: hmatrix, assumes Storable elements Vec, but the documentation states: Low Dimension : Although the dimensionality is limited only by what GHC will handle, the library is meant for 2,3 and 4 dimensions. For general linear algebra, check out the excellent hmatrix library and blas bindings I looked into the code and the documentation of many more libraries but nothing seems to suit my needs :-(. Update Since there seems to be nothing, I started a project on GitHub which aims to develop such a library. The current state is very minimalistic, not optimized for speed at all and only the most basic functions have tests and therefore should work. But should you be interested in using or helping out developing it: Contact me (you'll find my mail address on my web site) or send pull requests.

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  • std::vector elements initializing

    - by Chameleon
    std::vector<int> v1(1000); std::vector<std::vector<int>> v2(1000); std::vector<std::vector<int>::const_iterator> v3(1000); How elements of these 3 vectors initialized? About int, I test it and I saw that all elements become 0. Is this standard? I believed that primitives remain undefined. I create a vector with 300000000 elements, give non-zero values, delete it and recreate it, to avoid OS memory clear for data safety. Elements of recreated vector were 0 too. What about iterator? Is there a initial value (0) for default constructor or initial value remains undefined? When I check this, iterators point to 0, but this can be OS When I create a special object to track constructors, I saw that for first object, vector run the default constructor and for all others it run the copy constructor. Is this standard? Is there a way to completely avoid initialization of elements? Or I must create my own vector? (Oh my God, I always say NOT ANOTHER VECTOR IMPLEMENTATION) I ask because I use ultra huge sparse matrices with parallel processing, so I cannot use push_back() and of course I don't want useless initialization, when later I will change the value.

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  • Cast vector<T> to vector<const T>

    - by user345386
    I have a member variable of type vector (where is T is a custom class, but it could be int as well.) I have a function from which I want to return a pointer to this vector, but I don't want the caller to be able to change the vector or it's items. So I want the return type to be const vector* None of the casting methods I tried worked. The compiler keeps complaining that T is not compatible with const T. Here's some code that demonstrates the gist of what I'm trying to do; vector<int> a; const vector<const int>* b = (const vector<const int>* ) (&a); This code doesn't compile for me. Thanks in advance!

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  • Would vector of vectors be contiguous?

    - by user1150989
    I need to allocate a vector of rows where row contains a vector of rows. I know that a vector would be contiguous. I wanted to know whether a vector of vectors would also be contiguous. Example code is given below vector<long> firstRow; firstRow.push_back(0); firstRow.push_back(1); vector<long> secondRow; secondRow.push_back(0); secondRow.push_back(1); vector< vector < long> > data; data.push_back(firstRow); data.push_back(secondRow); Would the sequence in memory be 0 1 0 1?

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  • C++ vector reference parameter

    - by Archanimus
    Hello folks, let's say we have a class class MyClass { vector<vector<int > > myMatrice; public : MyClass(vector<vector<int > > &); } MyClass::MyClass(vector<vector<int > > & m) { myMatrice = m; } During the instanciation of MyClass, I pass a big vector < vector < int and I find that the object is actually copied and not only the reference, so it takes the double of the memory ... Please, can anyone help me out with this problem, I'm stuck since too many time ... And thanks a lot!

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  • Populate array from vector

    - by Zag zag..
    Hi, I would like to populate an 2 dimensional array, from a vector. I think the best way to explain myself is to put some examples (with a array of [3,5] length). When vector is: [1, 0] [ [4, 3, 2, 1, 0], [4, 3, 2, 1, 0], [4, 3, 2, 1, 0] ] When vector is: [-1, 0] [ [0, 1, 2, 3, 4], [0, 1, 2, 3, 4], [0, 1, 2, 3, 4] ] When vector is: [-2, 0] [ [0, 0, 1, 1, 2], [0, 0, 1, 1, 2], [0, 0, 1, 1, 2] ] When vector is: [1, 1] [ [2, 2, 2, 1, 0], [1, 1, 1, 1, 0], [0, 0, 0, 0, 0] ] When vector is: [0, 1] [ [2, 2, 2, 2, 2], [1, 1, 1, 1, 1], [0, 0, 0, 0, 0] ] Have you got any ideas, a good library or a plan? Any comments are welcome. Thanks. Note: I consulted Ruby "Matrix" and "Vector" classes, but I don't see any way to use it in my way... Edit: In fact, each value is the number of cells (from the current cell to the last cell) according to the given vector. If we take the example where the vector is [-2, 0], with the value *1* (at array[2, 3]): array = [ [<0>, <0>, <1>, <1>, <2>], [<0>, <0>, <1>, <1>, <2>], [<0>, <0>, <1>, *1*, <2>] ] ... we could think such as: The vector [-2, 0] means that -2 is for cols and 0 is for rows. So if we are in array[2, 3], we can move 1 time on the left (left because 2 is negative) with 2 length (because -2.abs == 2). And we don't move on the top or bottom, because of 0 for rows.

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  • How can I calculate a vertex normal for a hard edge?

    - by K.G.
    Here is a picture of a lovely polygon: Circled is a vertex, and numbered are its adjacent faces. I have calculated the normals of those faces as such (not yet normalized, 0-indexed): Vertex 1 normal 0: 0.000000 0.000000 -0.250000 Vertex 1 normal 1: 0.000000 0.000000 -0.250000 Vertex 1 normal 2: -0.250000 0.000000 0.000000 Vertex 1 normal 3: -0.250000 0.000000 0.000000 Vertex 1 normal 4: 0.250000 0.000000 0.000000 What I'm wondering is, how can I determine, taken as given that I want this vertex to represent a hard edge, whether its normal should be the normal of 1/2 or 3/4? My plan after I glanced at the sketch I used to put this together was "Ha! I'll just use whichever two faces have the same normal!" and now I see that there are two sets of two faces for which this is true. Is there a rule I can apply based on the face winding, angle of the adjacent edges, moon phase, coin flip, to consistently choose a normal direction for this box? For the record, all of the other polygons I plan to use will have their normals dictated in Maya, but after encountering this problem, it made me really curious.

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  • Moving objects colliding when using unalligned collision avoidance (steering)

    - by James Bedford
    I'm having trouble with unaligned collision avoidance for what I think is a rare case. I have set two objects to move towards each other but with a slight offset, so one of the objects is moving slightly upwards, and one of the objects is moving slightly downwards. In my unaligned collision avoidance steering algorithm I'm finding the points on the object's forward line and the other object's forward line where these two lines are the closest. If these closest points are within a collision avoidance distance, and if the distance between them is smaller than the two radii of the two object's bounding spheres, then the objects should steer away in the appropriate direction. The problem is that for my case, the closest points on the lines are calculated to be really far away from the actual collision point. This is because the two forward lines for each object are moving away from each other as the objects pass. The problem is that because of this, no steering takes place, and the two objects partially collide. Does anyone have any suggestions as to how I can correctly calculate the point of collision? Perhaps by somehow taking into account the size of the two objects?

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  • JavaScript computer algebra system

    - by Jonas
    I am looking for a simple computer algebra system (cas) for JavaScript but I can't find anything with google. I only need basic functionality: simplify expressions to some canonic form. Ability to check if two expressions are the same, i.e., a(x+y) == ax+ay parse mathematical formulas. I want it to be able to read expressions like ax²+4x. solve simple equations etc. Do you know of such a library?

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  • Converting a certain SQL query into relational algebra

    - by Fumler
    Just doing an assignment for my database course and I just want to double check that I've correctly wrapped my head around relational algebra. The SQL query: SELECT dato, SUM(pris*antall) AS total FROM produkt, ordre WHERE ordre.varenr = produkt.varenr GROUP BY dato HAVING total >= 10000 The relational algebra: stotal >= 10000( ?R(dato, total)( sordre.varenr = produkt.varenr( datoISUM(pris*antall(produkt x ordre)))) Is this the correct way of doing it?

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  • How can I move a polygon edge 1 unit away from the center?

    - by Stephen
    Let's say I have a polygon class that is represented by a list of vector classes as vertices, like so: var Vector = function(x, y) { this.x = x; this.y = y; }, Polygon = function(vectors) { this.vertices = vectors; }; Now I make a polygon (in this case, a square) like so: var poly = new Polygon([ new Vector(2, 2), new Vector(5, 2), new Vector(5, 5), new Vector(2, 5) ]); So, the top edge would be [poly.vertices[0], poly.vertices[1]]. I need to stretch this polygon by moving each edge away from the center of the polygon by one unit, along that edge's normal. The following example shows the first edge, the top, moved one unit up: The final polygon should look like this new one: var finalPoly = new Polygon([ new Vector(1, 1), new Vector(6, 1), new Vector(6, 6), new Vector(1, 6) ]); It is important that I iterate, moving one edge at a time, because I will be doing some collision tests after moving each edge. Here is what I tried so far (simplified for clarity), which fails triumphantly: for(var i = 0; i < vertices.length; i++) { var a = vertices[i], b = vertices[i + 1] || vertices[0]; // in case of final vertex var ax = a.x, ay = a.y, bx = b.x, by = b.y; // get some new perpendicular vectors var a2 = new Vector(-ay, ax), b2 = new Vector(-by, bx); // make into unit vectors a2.convertToUnitVector(); b2.convertToUnitVector(); // add the new vectors to the original ones a.add(a2); b.add(b2); // the rest of the code, collision tests, etc. } This makes my polygon start slowly rotating and sliding to the left, instead of what I need. Finally, the example shows a square, but the polygons in question could be anything. They will always be convex, and always with vertices in clockwise order.

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  • Looking for "bitmap-vector" image editor

    - by Borek
    I used to use PhotoImpact which is no longer developed so I'm looking for a replacement. What made PhotoImpact great to me was the ability to work in both bitmap and vector modes. What I mean by that: I could have an image or screenshot and easily add arrows, text captions or shapes to it. These shapes were vector objects so I could come back to them later and amend their properties easily. Software I know of: Paint.NET is purely bitmap so please don't recommend it - layers are not enough for my needs Drawing tools in MS Office work pretty much the way I'd like - you can paste an image and then add vector objects on top of it. It just doesn't feel right to have the full-fidelity original images stored as .docx or .pptx (I don't fully trust Word/Powerpoint that they don't compress the image) I'm not sure about GIMP but if it's just "better Paint.NET" (i.e., layers but no vector objects) I'm not interested Photoshop is out of question purely because of its price tag Corel killed PhotoImpact because they already had a competing product (Paint Shop Pro) but AFAIK it lacks vector features. Any tips for PhotoImpact alternatives would be very welcome.

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  • Relational algebra help?!

    - by Tom
    im new to relational algebra and finding it difficult. Ive answered a few questions, however they where relatively simple. Could do with help with these though. Database Patient (PatientCode, PatientSurname, PatientFirstname, PatientSex, PatientAge, PatientOccupation, PatientHeight, PatientWeight, PatientAddress) Doctor (DoctorCode, DoctorSurName, DoctorFirstName, DoctorPrivateAddress, MobileNo, Doctor Specilisim) Operation (Operation Code, PatientCode, DoctorCode, Date, Time, Result, OperationType) Is_Seen_By (PatientCode, DoctorCode, Date, Time). Q1. Find the surname and gender of the patients that have been operated on by doctor "DR333" and results have not been successful. Q2. Find the code of the operations that have been done on the 18th of November 2010 and have been successful, please also list the name of the doctors which were involved with the operation.

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  • KD-Trees and missing values (vector comparison)

    - by labratmatt
    I have a system that stores vectors and allows a user to find the n most similar vectors to the user's query vector. That is, a user submits a vector (I call it a query vector) and my system spits out "here are the n most similar vectors." I generate the similar vectors using a KD-Tree and everything works well, but I want to do more. I want to present a list of the n most similar vectors even if the user doesn't submit a complete vector (a vector with missing values). That is, if a user submits a vector with three dimensions, I still want to find the n nearest vectors (stored vectors are of 11 dimensions) I have stored. I have a couple of obvious solutions, but I'm not sure either one seem very good: Create multiple KD-Trees each built using the most popular subset of dimensions a user will search for. That is, if a user submits a query vector of thee dimensions, x, y, z, I match that query to my already built KD-Tree which only contains vectors of three dimensions, x, y, z. Ignore KD-Trees when a user submits a query vector with missing values and compare the query vector to the vectors (stored in a table in a DB) one by one using something like a dot product. This has to be a common problem, any suggestions? Thanks for the help.

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  • Direct3D Rotation Matrix from Vector and vice-versa

    - by Beta Carotin
    I need to compute a rotation matrix from a direction vector, and a direction vector from a rotation matrix. The up direction should correspond to the z-axis, forward is y and right is x; D3DXMATRIX m; // the rotation matrix D3DXVECTOR3 v; // this is the direction vector wich is given D3DXVECTOR3 r; // resulting direction vector float len = D3DXVec3Length(&v); // length of the initial direction vector // compute matrix D3DXMatrixLookAtLH(&m, &v, &D3DXVECTOR3(0,0,0), &D3DXVECTOR3(0,0,1)); // use the matrix on a vector { 0, len, 0 } D3DXVec3TransformCoord(&r, &D3DXVECTOR3(0,len,0), &m); Now, the vector r should be equal to v, but it isnt. What exactly do I have to do to get the results I need?

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  • Some questions about Vector in STL

    - by skydoor
    I have some questions about vector in STL to clarify..... Where are the objects in vector allocated? heap? does vector have boundary check? If the index out of the boundary, what error will happen? Why array is faster than vector? Is there any case in which vector is not applicable but array is a must?

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  • some qeustions about Vector in STL

    - by skydoor
    I have some questions about vector in STL to clarify..... 1 Where are the objects in vector allocated? heap? 2 does vector have boundary check? If the index out of the boundary, what error will happen? 3 Why array is faster than vector? 4 Is there any case in which vector is not applicable but array is a must?

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  • Finding character in String in Vector.

    - by SoulBeaver
    Judging from the title, I kinda did my program in a fairly complicated way. BUT! I might as well ask anyway xD This is a simple program I did in response to question 3-3 of Accelerated C++, which is an awesome book in my opinion. I created a vector: vector<string> countEm; That accepts all valid strings. Therefore, I have a vector that contains elements of strings. Next, I created a function int toLowerWords( vector<string> &vec ) { for( int loop = 0; loop < vec.size(); loop++ ) transform( vec[loop].begin(), vec[loop].end(), vec[loop].begin(), ::tolower ); that splits the input into all lowercase characters for easier counting. So far, so good. I created a third and final function to actually count the words, and that's where I'm stuck. int counter( vector<string> &vec ) { for( int loop = 0; loop < vec.size(); loop++ ) for( int secLoop = 0; secLoop < vec[loop].size(); secLoop++ ) { if( vec[loop][secLoop] == ' ' ) That just looks ridiculous. Using a two-dimensional array to call on the characters of the vector until I find a space. Ridiculous. I don't believe that this is an elegant or even viable solution. If it was a viable solution, I would then backtrack from the space and copy all characters I've found in a separate vector and count those. My question then is. How can I dissect a vector of strings into separate words so that I can actually count them? I thought about using strchr, but it didn't give me any epiphanies.

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  • C++ STL Map vs Vector speed

    - by sub
    In the interpreter for my experimental programming language I have a symbol table. Each symbol consists of a name and a value (the value can be e.g.: of type string, int, function, etc.). At first I represented the table with a vector and iterated through the symbols checking if the given symbol name fitted. Then I though using a map, in my case map<string,symbol>, would be better than iterating through the vector all the time but: It's a bit hard to explain this part but I'll try. If a variable is retrieved the first time in a program in my language, of course its position in the symbol table has to be found (using vector now). If I would iterate through the vector every time the line gets executed (think of a loop), it would be terribly slow (as it currently is, nearly as slow as microsoft's batch). So I could use a map to retrieve the variable: SymbolTable[ myVar.Name ] But think of the following: If the variable, still using vector, is found the first time, I can store its exact integer position in the vector with it. That means: The next time it is needed, my interpreter knows that it has been "cached" and doesn't search the symbol table for it but does something like SymbolTable.at( myVar.CachedPosition ). Now my (rather hard?) question: Should I use a vector for the symbol table together with caching the position of the variable in the vector? Should I rather use a map? Why? How fast is the [] operator? Should I use something completely different?

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  • C++ std::vector problems

    - by Faur Ioan-Aurel
    For 2 days i tried to explain myself some of the things that are happening in my c++ code,and i can't get a good explanation.I must say that i'm more a java programmer.Long time i used quite a bit the C language but i guess Java erased those skills and now i'm hitting a wall trying to port a few classes from java to c++. So let's say that we have this 2 classes: class ForwardNetwork { protected: ForwardLayer* inputLayer; ForwardLayer* outputLayer; vector<ForwardLayer* > layers; public: void ForwardNetwork::getLayers(std::vector< ForwardLayer* >& result ) { for(int i= 0 ;i< layers.size(); i++){ ForwardLayer* lay = dynamic_cast<ForwardLayer*>(this->layers.at(i)); if(lay != NULL) result.push_back(lay); else cout << "Layer at#" << i << " is null" << endl; } } void ForwardNetwork::addLayer ( ForwardLayer* layer ) { if(layer != NULL) cout << "Before push layer is not null" << endl; //setup the forward and back pointer if ( this->outputLayer != NULL ) { layer->setPrevious ( this->outputLayer ); this->outputLayer->setNext ( layer ); } //update the input layer and outputLayer variables if ( this->layers.size() == 0 ) this->inputLayer = this->outputLayer = layer; else this->outputLayer = layer; //push layer in vector this->layers.push_back ( layer ); for(int i = 0; i< layers.size();i++) if(layers[i] != NULL) cout << "Check::Layer[" << i << "] is not null!" << endl; } }; Second class: class Backpropagation : public Train { public: Backpropagation::Backpropagation ( FeedForwardNetwork* network ){ this->network = network; vector<FeedforwardLayer*> vec; network->getLayers(vec); } }; Now if i add from main() some layers into network via addLayer(..) method it's all good.My vector is just as it should.But after i call Backpropagation() constructor with a network object ,when i enter getLayers(), some of my objects from vector have their address set to NULL(they are randomly chosen:for example if i run my app once with 3 layer's into vector ,the first object from vector is null.If i run it second time first 2 objects are null,third time just first object null and so on). Now i can't explain why this is happening.I must say that all the objects that should be in vector they also live inside the network and they are not NULL; This happens everywhere after i done with addLayer() so not just in the getLayers(). I cant get a good grasp to this problem.I thought first that i might modify my vector.But i can't find such thing. Also why if the reference from vector is NULL ,the reference that lives inside ForwardNetwork as a linked list (inputLayer and outputLayer) is not NULL? I must ask for your help.Please ,if you have some advices don't hesitate! PS: as compiler i use g++ part of gcc 4.6.1 under ubuntu 11.10

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  • Weird behaviour with vector::erase and std::remove_if with end range different from vector.end()

    - by Edison Gustavo Muenz
    Hi, I need to remove elements from the middle of a std::vector. So I tried: struct IsEven { bool operator()(int ele) { return ele % 2 == 0; } }; int elements[] = {1, 2, 3, 4, 5, 6}; std::vector<int> ints(elements, elements+6); std::vector<int>::iterator it = std::remove_if(ints.begin() + 2, ints.begin() + 4, IsEven()); ints.erase(it, ints.end()); After this I would expect that the ints vector have: [1, 2, 3, 5, 6]. In the debugger of Visual studio 2008, after the std::remove_if line, the elements of ints are modified, I'm guessing I'm into some sort of undefined behaviour here. So, how do I remove elements from a Range of a vector?

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