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  • What is a truly empty std::vector in C++?

    - by RyanG
    I've got a two vectors in class A that contain other class objects B and C. I know exactly how many elements these vectors are supposed to hold at maximum. In the initializer list of class A's constructor, I initialize these vectors to their max sizes (constants). If I understand this correctly, I now have a vector of objects of class B that have been initialized using their default constructor. Right? When I wrote this code, I thought this was the only way to deal with things. However, I've since learned about std::vector.reserve() and I'd like to achieve something different. I'd like to allocate memory for these vectors to grow as large as possible because adding to them is controlled by user-input, so I don't want frequent resizings. However, I iterate through this vector many, many times per second and I only currently work on objects I've flagged as "active". To have to check a boolean member of class B/C on ever iteration is silly. I don't want these objects to even BE there for my iterators to see when I run through this list. Is reserving the max space ahead of time and using push_back to add a new object to the vector a solution to this?

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  • C++: getting the address of the start of an std::vector ?

    - by shoosh
    Sometimes it is useful to use the starting address of an std::vector and temporarily treat that address as the address of a regularly allocated buffer. For instance replace this: char* buf = new char[size]; fillTheBuffer(buf, size); useTheBuffer(buf, size); delete[] buf; With This: vector<char> buf(size); fillTheBuffer(&buf[0], size); useTheBuffer(&buf[0], size); The advantage of this is of course that the buffer is deallocated automatically and I don't have to worry about the delete[]. The problem I'm having with this is when size == 0. In that case the first version works ok. An empty buffer is "allocated" and the subsequent functions do nothing size they get size == 0. The second version however fails if size == 0 since calling buf[0] may rightly contain an assertion that 0 < size. So is there an alternative to the idiom &buf[0] that returns the address of the start of the vector even if the vector is empty? I've also considered using buf.begin() but according to the standard it isn't even guaranteed to return a pointer.

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  • Adding cards to a vector for computer card game

    - by Tucker Morgan
    I am writing a Card game that has a deck size of 30 cards, each one of them has to be a unique, or at least a another (new XXXX) statement in a .push_back function, into a vector. Right now my plan is to add them to a vector one at a time with four separate, depending on what deck type you choose, collections of thirty .push_back functions. If the collection of card is not up for customization, other than what one of the four suits you pick, is there a quicker way of doing this, seems kinda tedious, and something that someone would have found a better way of doing.

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  • How to convert poor quality bitmap image to vector?

    - by Macha
    I'm designing a website for a group which has lost the original digital image for their logo. The only file they have of it is a jpg which was embedded into a word document. The image has everything possible wrong with it: Anti-aliased onto a white background where it should be transparent Image artefacts Resized downwards poorly. Lines that should be straight and solid aren't. I've currently used the wand tool to get rid of the white background, and stuck it on the website, but it's poor quality makes it stick out like a sore thumb. I need a few different sizes of it to use, so how would I go about creating a vector image based on it?

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  • Rotation matrix for a 3D vector

    - by Shashwat
    I have a direction vector on which I have to apply some rotation to align it to positive z-axis. To use Matrix.CreateRotationX(angle) of XNA, I need the angle for which I'd have to compute cos or tan inverse. I think this is a complex task to do. Also, eventually those are also converted to sin(angle) and cos(angle) in the matrix. Is there any inbuilt way to create rotation matrix from a 3D vector? However, I can write the function but still asking if there is one already there.

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  • infer half vector length in BRDF

    - by cician
    it's my first question on stack. Is it possible to infer length of the half angle vector for specular lighting from N·L and N·V without the whole view and light vectors? I may be completely off-track, but I have this gut feeling it's possible... Why? I'm working on a skin shader and I'm already doing one texture lookup with N·L+N·E and one texture lookup for specular with N·H+N·V. The latter one can be transformed into N·L+N·E lookup if only I had the half vector length. Doing so could simplify the shader a bit and move some operations into the pre-computed lookup texture. It would make a huge difference since I'm trying to squeeze as much functionality as possible to a single pass mobile version so instruction count matters. Thanks.

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  • A "quick" vector editor (SVG) for Linux (for annotating images?)

    - by sdaau
    I often need to take a bitmap (.png) image, and draw some lines or text on top of it, and possibly export a new, thusly "annotated" image. I know I can basically do all this in inkscape - but inkscape is a complex program, and it needs almost a minute to start up properly on my PCs. So I was thinking - is there something like a "mini" vector editor for Linux, which would start up fast, and allow me to: Right-click, open an image in this editor program The program scales the active "document"/"window size" to the size of the image I can zoom in/zoom out (and possibly crop) the image I can add at least lines, boxes and text in different colors? A bonus for me would be to have the overlay graphics saved as SVG format, say with the same filename as the image - as in, "image.png.svg" being saved in the same directory where the original "image.png" is located (thus allowing opening and editing these "annotations" further, either in this editor, or possibly in inkscape). And another bonus would be the export of the annotated image to a bitmap. Anyone know about anything like this?

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  • no match for operator= using a std::vector

    - by Max
    I've got a class declared like this: class Level { private: std::vector<mapObject::MapObject> features; (...) }; and in one of its member functions I try to iterate through that vector like this: vector<mapObject::MapObject::iterator it; for(it=features.begin(); it<features.end(); it++) { /* loop code */ } This seems straightforward to me, but g++ gives me this error: src/Level.cpp:402: error: no match for ‘operator=’ in ‘it = ((const yarl::level::Level*)this)-yarl::level::Level::features.std::vector<_Tp, _Alloc::begin [with _Tp = yarl::mapObject::MapObject, _Alloc = std::allocator<yarl::mapObject::MapObject>]()’ /usr/include/c++/4.4/bits/stl_iterator.h:669: note: candidates are: __gnu_cxx::__normal_iterator<yarl::mapObject::MapObject*,std::vector & __gnu_cxx::__normal_iterator<yarl::mapObject::MapObject*,std::vector >::operator=(const __gnu_cxx::__normal_iterator<yarl::mapObject::MapObject*, ``std::vector<yarl::mapObject::MapObject, std::allocator<yarl::mapObject::MapObject> > >&) Anyone know why this is happening?

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  • Basic question about std::vector instantiation

    - by recipriversexclusion
    This looks simple but I am confused: The way I create a vector of hundred, say, ints is std::vector<int> *pVect = new std::vector<int>(100); However, looking at std::vector's documentation I see that its constructor is of the form explicit vector ( size_type n, const T& value= T(), const Allocator& = Allocator() ); So, how does the previous one work? Does new call the constructor with an initialization value obtained from the default constructor? If that is the case, would std::vector<int, my_allocator> *pVect = new std::vector<int>(100, my_allocator); where I pass my own allocator, also work?

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  • How can I eliminate an element in a vector if a condition is met

    - by michael
    Hi, I have a vector of Rect: vector<Rect> myRecVec; I would like to remove the ones which are overlapping in the vector: So I have 2 nested loop like this: vector<Rect>::iterator iter1 = myRecVec.begin(); vector<Rect>::iterator iter2 = myRecVec.begin(); while( iter1 != myRecVec.end() ) { Rectangle r1 = *iter1; while( iter2 != myRecVec.end() ) { Rectangle r2 = *iter1; if (r1 != r2) { if (r1.intersects(r2)) { // remove r2 from myRectVec } } } } My question is how can I remove r2 from the myRectVect without screwing up both my iterators? Since I am iterating a vector and modifying the vector at the same time? I have thought about putting r2 in a temp rectVect and then remove them from the rectVect later (after the iteration). But how can I skip the ones in this temp rectVect during iteration?

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  • Why can't I access a const vector with iterator?

    - by tsubasa
    My example is as below. I found out the problem is with "const" in function void test's parameter. I don't know why the compiler does not allow. Could anybody tell me? Thanks. vector<int> p; void test(const vector<int> &blah) { vector<int>::iterator it; for (it=blah.begin(); it!=blah.end(); it++) { cout<<*it<<" "; } } int main() { p.push_back(1); p.push_back(2); p.push_back(3); test(p); return 0; }

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  • Reusing a vector in C++

    - by Bobby
    I have a vector declared as a global variable that I need to be able to reuse. For example, I am reading multiple files of data, parsing the data to create objects that are then stored in a vector. vector<Object> objVector(100); void main() { while(THERE_ARE_MORE_FILES_TO_READ) { // Pseudocode ReadFile(); ParseFileIntoVector(); ProcessObjectsInVector(); /* Here I want to 'reset' the vector to 100 empty objects again */ } } Can I reset the vector to be "vector objVector(100)" since it was initially allocated on the stack? If I do "objVector.clear()", it removes all 100 objects and I would have a vector with a size of 0. I need it to be a size of 100 at the start of every loop.

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  • Deleting a element from a vector of pointers in C++.

    - by Kranar
    I remember hearing that the following code is not C++ compliant and was hoping someone with much more C++ legalese than me would be able to confirm or deny it. std::vector<int*> intList; intList.push_back(new int(2)); intList.push_back(new int(10)); intList.push_back(new int(17)); for(std::vector<int*>::iterator i = intList.begin(); i != intList.end(); ++i) { delete *i; } intList.clear() The rationale was that it is illegal for a vector to contain pointers to invalid memory. Now obviously my example will compile and it will even work on all compilers I know of, but is it standard compliant C++ or am I supposed to do the following, which I was told is in fact the standard compliant approach: while(!intList.empty()) { int* element = intList.back(); intList.pop_back(); delete element; }

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  • hash tables and 2d vectors

    - by Sunil
    I want to push a 2d vector into a hash table row by row and later search for a row (vector) in the hash table and want to be able to find it. I want to do something like #include <iostream> #include <set> #include <vector> using namespace std; int main(){ std::set < vector<int> > myset; vector< vector<int> > v; int k = 0; for ( int i = 0; i < 5; i++ ) { v.push_back ( vector<int>() ); for ( int j = 0; j < 5; j++ ) v[i].push_back ( k++ ); } for ( int i = 0; i < 5; i++ ) { std::copy(v[i].begin(),v[i].end(),std::inserter(myset)); // This is not correct but what is the right way ? // and also here, I want to search for a particular vector if it exists in the table. for ex. the second row of vector v. } return 0; } I'm not sure how to insert and look up a vector in a set. So if nybody could guide me, it will be helpful. Thanks

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  • How to implement a simple bullet trajectory

    - by AirieFenix
    I searched and searched and although it's a fair simple question, I don't find the proper answer but general ideas (which I already have). I have a top-down game and I want to implement a gun which shoots bullets that follow a simple path (no physics nor change of trajectory, just go from A to B thing). a: vector of the position of the gun/player. b: vector of the mouse position (cross-hair). w: the vector of the bullet's trajectory. So, w=b-a. And the position of the bullet = [x=x0+speed*time*normalized w.x , y=y0+speed*time * normalized w.y]. I have the constructor: public Shot(int shipX, int shipY, int mouseX, int mouseY) { //I get mouse with Gdx.input.getX()/getY() ... this.shotTime = TimeUtils.millis(); this.posX = shipX; this.posY = shipY; //I used aVector = aVector.nor() here before but for some reason didn't work float tmp = (float) (Math.pow(mouseX-shipX, 2) + Math.pow(mouseY-shipY, 2)); tmp = (float) Math.sqrt(Math.abs(tmp)); this.vecX = (mouseX-shipX)/tmp; this.vecY = (mouseY-shipY)/tmp; } And here I update the position and draw the shot: public void drawShot(SpriteBatch batch) { this.lifeTime = TimeUtils.millis() - this.shotTime; //position = positionBefore + v*t this.posX = this.posX + this.vecX*this.lifeTime*speed*Gdx.graphics.getDeltaTime(); this.posY = this.posY + this.vecY*this.lifeTime*speed*Gdx.graphics.getDeltaTime(); ... } Now, the behavior of the bullet seems very awkward, not going exactly where my mouse is (it's like the mouse is 30px off) and with a random speed. I know I probably need to open the old algebra book from college but I'd like somebody says if I'm in the right direction (or points me to it); if it's a calculation problem, a code problem or both. Also, is it possible that Gdx.input.getX() gives me non-precise position? Because when I draw the cross-hair it also draws off the cursor position. Sorry for the long post and sorry if it's a very basic question. Thanks!

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  • Best way to implement a simple bullet trajectory

    - by AirieFenix
    I searched and searched and although it's a fair simple question, I don't find the proper answer but general ideas (which I already have). I have a top-down game and I want to implement a gun which shoots bullets that follow a simple path (no physics nor change of trajectory, just go from A to B thing). a: vector of the position of the gun/player. b: vector of the mouse position (cross-hair). w: the vector of the bullet's trajectory. So, w=b-a. And the position of the bullet = [x=x0+speed*time*normalized w.x , y=y0+speed*time * normalized w.y]. I have the constructor: public Shot(int shipX, int shipY, int mouseX, int mouseY) { //I get mouse with Gdx.input.getX()/getY() ... this.shotTime = TimeUtils.millis(); this.posX = shipX; this.posY = shipY; //I used aVector = aVector.nor() here before but for some reason didn't work float tmp = (float) (Math.pow(mouseX-shipX, 2) + Math.pow(mouseY-shipY, 2)); tmp = (float) Math.sqrt(Math.abs(tmp)); this.vecX = (mouseX-shipX)/tmp; this.vecY = (mouseY-shipY)/tmp; } And here I update the position and draw the shot: public void drawShot(SpriteBatch batch) { this.lifeTime = TimeUtils.millis() - this.shotTime; //position = positionBefore + v*t this.posX = this.posX + this.vecX*this.lifeTime*speed*Gdx.graphics.getDeltaTime(); this.posY = this.posY + this.vecY*this.lifeTime*speed*Gdx.graphics.getDeltaTime(); ... } Now, the behavior of the bullet seems very awkward, not going exactly where my mouse is (it's like the mouse is 30px off) and with a random speed. I know I probably need to open the old algebra book from college but I'd like somebody says if I'm in the right direction (or points me to it); if it's a calculation problem, a code problem or both. Also, is it possible that Gdx.input.getX() gives me non-precise position? Because when I draw the cross-hair it also draws off the cursor position. Sorry for the long post and sorry if it's a very basic question. Thanks!

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  • Sort a Vector of custom objects

    - by user307818
    I'm trying to sort a Vector in java but my Vector is not a vector of int, it is a vector of objects the object is: public MyObject() { numObj = 0; price = new Price(); pax = new Pax(); } so I have a Vector of MyObject and I want to order it by numObject, how do i do it, I'm new in java? Thank you so much for all your help.

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  • sort a custum Vector of objects

    - by user307818
    I'm trying to sort a Vector in java but my Vector is not a vector of int, it is a vector of objects the object is : public MyObject() { numObj = 0; price = new Price(); pax = new Pax(); } so I have a Vector of MyObject and I want to order it by numObject, how do i do it, i'm new in java? thank you so much for all your help

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  • Calculating the 2D edge normals of a triangle

    - by Kazade
    What's a reliable way to calculate a 2D normal vector for each edge of a triangle, so that each normal is pointing outwards from the triangle? To clarify, given any triangle - for each edge (e.g p2-p1), I need to calculate a 2D normal vector pointing away from the triangle at right angles to the edge (for simplicity we can assume that the points are being specified in an anti-clockwise direction). I've coded a couple of hacky attempts, but I'm sure I'm overlooking some simple method and Google isn't being that helpful today - that and I haven't had my daily caffeine yet!

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  • Finding vectors with two points

    - by Christian Careaga
    We're are trying to get the direction of a projectile but we can't find out how For example: [1,1] will go SE [1,-1] will go NE [-1,-1] will go NW and [-1,1] will go SW we need an equation of some sort that will take the player pos and the mouse pos and find which direction the projectile needs to go. Here is where we are plugging in the vectors: def update(self): self.rect.x += self.vector[0] self.rect.y += self.vector[1] Then we are blitting the projectile at the rects coords.

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  • Intelligence as a vector quantity

    - by Senthil Kumaran
    I am reading this wonderful book called "Coders at Work: Reflections on the Craft of Programming" by Peter Seibel and I am at part wherein the conversation is with Joshua Bloch and I found this answer which is an important point for a programmer. The paragraph, goes something like this. There's this problem, which is, programming is so much of an intellectual meritocracy and often these people are the smartest people in the organization; therefore they figure they should be allowed to make all the decisions. But merely the fact they are the smartest people in the organization does not mean that they should be making all the decisions, because intelligence is not a scalar quantity; it's a vector quantity. Here at the last sentence, I fail to get the insight which is he trying to share. Can someone explain it in a little further as what he means by a vector quantity, possibly trying to present the same insight. Further down, I get the point that he is not taking about having an organization where non-technical people (sometimes clueless) can be managers of the technical people for some reason that they can spend more time to write emails well, because the very next statement following the above paragraph was. And if you lack empathy or emotional intelligence, then you shouldn't be designing APIs or GUIs or languages. I understand that he is saying that in Software engineering, programmers should know how the users will see their product and design for them. I felt the above paragraph was very interesting.

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