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  • prevent using functions before initialization, constructors-like in C

    - by Hernán Eche
    This is the way I get to prevent funA,funB,funC, etc.. for being used before init #define INIT_KEY 0xC0DE //any number except 0, is ok static int initialized=0; int Init() { //many init task initialized=INIT_KEY; } int funA() { if (initialized!=INIT_KEY) return 1 //.. } int funB() { if (initialized!=INIT_KEY) return 1 //.. } int funC() { if (initialized!=INIT_KEY) return 1 //.. } The problem with this approach is that if some of those function is called within a loop so "if (initialized!=INIT_KEY)" is called again, and again, although it's not necessary. It's a good example of why constructors are useful haha, If it were an object I would be sure that when was created initialization was called, but in C, I don't know how to do it. Any other ideas are welcome!

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  • +(void) initialize in objecive c class static variables construstor

    - by sugar
    I found some sample code from here. static UIImage *backgroundImageDepressed; /** * */ @implementation DecimalPointButton + (void) initialize { backgroundImageDepressed = [[UIImage imageNamed:@"decimalKeyDownBackground.png"] retain]; } is it something like this - +(void) initialize method initialize static variables of a class ( interface ) in objective c ? I have never seen this before. Please need your guidance on it. Thanks in advance for sharing your great knowledge. Sagar

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  • Is the old vector get cleared? If yes, how and when?

    - by user180866
    I have the following code: void foo() { vector<double> v(100,1); // line 1 // some code v = vector<double>(200,2); // line 2 // some code } what happened to the vector of size 100 after the second line? Is it gets cleared by itself? If the answer is yes, how and when it is cleared? By the way, is there any other "easy and clean" ways to change the vector as in line 2? I don't want things like v.resize(200); for (int i=0; i<200; i++) v[i] = 2;

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  • How to differentiate two constructors with the same parameters?

    - by cibercitizen1
    Suppose we want two constructors for a class representing complex numbers: Complex (double re, double img) // construct from cartesian coordinates Complex (double A, double w) // construct from polar coordinates but the parameters (number and type) are the same: what is the more elegant way to identify what is intended? Adding a third parameter to one of the constructors?

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  • c++/boost: use tuple ctors when subclassing

    - by bbb
    Hi there, is there some way to use a boost tuple's ctors as an addition to the subclass methods (and ctors) like here? // typedef boost::tuple<int, SomeId, SomeStatus> Conn; // Conn(1); // works and initializes using default ctors of Some* struct Conn : boost::tuple<int, AsynchId, AccDevRetStatus> {}; Conn(1); // "no matching function call" (but i want it so much) T.H.X.

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  • copy C'tor with operator= | C++

    - by user2266935
    I've got this code here: class DerivedClass : public BaseClass { SomeClass* a1; Someclass* a2; public: //constructors go here ~DerivedClass() { delete a1; delete a2;} // other functions go here .... }; My first question is as follows: Can I write an "operator=" to "DerivedClass" ? (if your answer is yes, could you show me how?) My second question is: If the answer to the above is yes, could you show me how to make an "copy c'tor" using the "operator=" that you wrote beforehand (if that is even possible)? Your help would be much appreciated !

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  • Should constant contructor aguments be passed by reference or value?

    - by Mike
    When const values are passed to an object construct should they be passed by reference or value? If you pass by value and the arguments are immediately fed to initializes are two copies being made? Is this something that the compiler will automatically take care of. I have noticed that all textbook examples of constructors and intitializers pass by value but this seems inefficient to me. class Point { public: int x; int y; Point(const int _x, const int _y) : x(_x), y(_y) {} }; int main() { const int a = 1, b = 2; Point p(a,b); Point q(3,5); cout << p.x << "," << p.y << endl; cout << q.x << "," << q.y << endl; } vs. class Point { public: int x; int y; Point(const int& _x, const int& _y) : x(_x), y(_y) {} }; Both compile and do the same thing but which is correct?

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  • List with non-null elements ends up containing null. A synchronization issue?

    - by Alix
    Hi. First of all, sorry about the title -- I couldn't figure out one that was short and clear enough. Here's the issue: I have a list List<MyClass> list to which I always add newly-created instances of MyClass, like this: list.Add(new MyClass()). I don't add elements any other way. However, then I iterate over the list with foreach and find that there are some null entries. That is, the following code: foreach (MyClass entry in list) if (entry == null) throw new Exception("null entry!"); will sometimes throw an exception. I should point out that the list.Add(new MyClass()) are performed from different threads running concurrently. The only thing I can think of to account for the null entries is the concurrent accesses. List<> isn't thread-safe, after all. Though I still find it strange that it ends up containing null entries, instead of just not offering any guarantees on ordering. Can you think of any other reason? Also, I don't care in which order the items are added, and I don't want the calling threads to block waiting to add their items. If synchronization is truly the issue, can you recommend a simple way to call the Add method asynchronously, i.e., create a delegate that takes care of that while my thread keeps running its code? I know I can create a delegate for Add and call BeginInvoke on it. Does that seem appropriate? Thanks.

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  • creating new instance fails PHP

    - by as3isolib
    I am relatively new to PHP and having some decent success however I am running into this issue: If I try to create a new instance of the class GenericEntryVO, I get a 500 error with little to no helpful error information. However, if I use a generic object as the result, I get no errors. I'd like to be able to cast this object as a GenericEntryVO as I am using AMFPHP to communicate serialize data with a Flex client. I've read a few different ways to create constructors in PHP but the typical 'public function Foo()' for a class Foo was recommended for PHP 5.4.4 //in my EntryService.php class public function getEntryByID($id) { $link = mysqli_connect("localhost", "root", "root", "BabyTrackingAppDB"); if (mysqli_connect_errno()) { printf("Connect failed: %s\n", mysqli_connect_error()); exit(); } $query = "SELECT * FROM Entries WHERE id = '$id' LIMIT 1"; if ($result = mysqli_query($link, $query)) { // $entry = new GenericEntryVO(); this is where the problem lies! while ($row = mysqli_fetch_row($result)) { $entry->id = $row[0]; $entry->entryType = $row[1]; $entry->title = $row[2]; $entry->description = $row[3]; $entry->value = $row[4]; $entry->created = $row[5]; $entry->updated = $row[6]; } } mysqli_free_result($result); mysqli_close($link); return $entry; } //my GenericEntryVO.php class <?php class GenericEntryVO { public function __construct() { } public $id; public $title; public $entryType; public $description; public $value; public $created; public $updated; // public $properties; } ?>

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  • Can I pass a pointer to a superclass, but create a copy of the child?

    - by Alex
    I have a function that takes a pointer to a superclass and performs operations on it. However, at some point, the function must make a deep copy of the inputted object. Is there any way I can perform such a copy? It occurred to me to make the function a template function and simply have the user pass the type, but I hold out hope that C++ offers a more elegant solution.

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  • Copy object using pointer (templates)

    - by Azodious
    How the push_back of stl::vector is implemented so it can make copy of any datatype .. may be pointer, double pointer and so on ... I'm implementing a template class having a function push_back almost similar to vector. Within this method a copy of argument should be inserted in internal memory allocated memory. but the argument is a pointer. (an object pointer). Can you pls tell how to create copy from pointer. so that if i delete the pointer in caller still the copy exists in my template class? Code base is as follows: template<typename T> class Vector { public: void push_back(const T& val_in) { T* a = *(new T(val_in)); m_pData[SIZE++] = a; } } Caller: Vector<MyClass*> v(3); MyClass* a = new MyClass(); a->a = 0; a->b = .5; v.push_back(a); delete a; Thanks.

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  • Templates, interfaces (multiple inheritance) and static functions (named constructors)

    - by fledgling Cxx user
    Setup I have a graph library where I am trying to decompose things as much as possible, and the cleanest way to describe it that I found is the following: there is a vanilla type node implementing only a list of edges: class node { public: int* edges; int edge_count; }; Then, I would like to be able to add interfaces to this whole mix, like so: template <class T> class node_weight { public: T weight; }; template <class T> class node_position { public: T x; T y; }; and so on. Then, the actual graph class comes in, which is templated on the actual type of node: template <class node_T> class graph { protected: node_T* nodes; public: static graph cartesian(int n, int m) { graph r; r.nodes = new node_T[n * m]; return r; } }; The twist is that it has named constructors which construct some special graphs, like a Cartesian lattice. In this case, I would like to be able to add some extra information into the graph, depending on what interfaces are implemented by node_T. What would be the best way to accomplish this? Possible solution I thought of the following humble solution, through dynamic_cast<>: template <class node_T, class weight_T, class position_T> class graph { protected: node_T* nodes; public: static graph cartesian(int n, int m) { graph r; r.nodes = new node_T[n * m]; if (dynamic_cast<node_weight<weight_T>>(r.nodes[0]) != nullptr) { // do stuff knowing you can add weights } if (dynamic_cast<node_position<positionT>>(r.nodes[0]) != nullptr) { // do stuff knowing you can set position } return r; } }; which would operate on node_T being the following: template <class weight_T, class position_T> class node_weight_position : public node, public node_weight<weight_T>, public node_position<position_T> { // ... }; Questions Is this -- philosophically -- the right way to go? I know people don't look nicely at multiple inheritance, though with "interfaces" like these it should all be fine. There are unfortunately problems with this. From what I know at least, dynamic_cast<> involves quite a bit of run-time overhead. Hence, I run into a problem with what I had solved earlier: writing graph algorithms that require weights independently of whether the actual node_T class has weights or not. The solution with this 'interface' approach would be to write a function: template <class node_T, class weight_T> inline weight_T get_weight(node_T const & n) { if (dynamic_cast<node_weight<weight_T>>(n) != nullptr) { return dynamic_cast<node_weight<weight_T>>(n).weight; } return T(1); } but the issue with it is that it works using run-time information (dynamic_cast), yet in principle I would like to decide it at compile-time and thus make the code more efficient. If there is a different solution that would solve both problems, especially a cleaner and better one than what I have, I would love to hear about it!

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  • Is new int[10]() valid c++?

    - by Naveen
    While trying to answer this question I found that the code int* p = new int[10](); compiles fine with VC9 compiler and initializes the integers to 0. So my questions are: First of all is this valid C++ or is it a microsoft extension? Is it guaranteed to initialize all the elements of the array? Also, is there any difference if I do new int; or new int();? Does the latter guarantee to initialize the variable?

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  • C++: Could Polymorphic Copy Constructors work?

    - by 0xC0DEFACE
    Consider: class A { public: A( int val ) : m_ValA( val ) {} A( const A& rhs ) {} int m_ValA; }; class B : public A { public: B( int val4A, int val4B ) : A( val4A ), m_ValB( val4B ) {} B( const B& rhs ) : A( rhs ), m_ValB( rhs.m_ValB ) {} int m_ValB; }; int main() { A* b1 = new B( 1, 2 ); A* b2 = new A( *b1 ); // ERROR...but what if it could work? return 0; } Would C++ be broken if "new A( b1 )" was able to resolve to creating a new B copy and returning an A? Would this even be useful?

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  • Purpose of PHP constructors

    - by Bharanikumar
    Hi, I am working with classes and object class structure, but not at a complex level – just classes and functions, then, in one place, instantiation. As to __construct and __destruct, please tell me very simply: what is the purpose of constructors and destructors? I know the school level theoretical explanation, but i am expecting something like in real world, as in which situations we have to use them. Provide also an example, please. Regards

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  • Why can't I construct an std::istream_iterator with an unnamed temporary?

    - by Stumped6789
    g++ allows this construction of an istream_iterator from an ifstream instance: std::ifstream ifstr("test.txt"); std::istream_iterator<std::string> iter1(ifstr); ...but it doesn't allow the same construction with an unnamed temporary: std::istream_iterator<std::string> iter2(std::ifstream("test.txt")); This gives: error: no matching function for call to ‘std::istream_iterator, ptrdiff_t::istream_iterator(std::ifstream)’ Does anyone know why this doesn't work? - thanks!

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  • Are high office partitions as effective as private offices?

    - by CraigS
    I'm currently reading DeMarco and Lister's Peopleware, and I've been struck (as everyone is) by their comments about noise reduction via using private offices, and the effect this has on productivity. Private offices are probably not going to happen at my workplace, but I'm wondering if high cubicle partitions (say, 6 feet) might be nearly as good? I imagine they wouldn't deflect quite as much noise, but they would have some effect. One down-side is that the center cubicles would have less natural light. That seems quite a big downer to me. I'd be interested to hear what peoples experiences are.

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  • Snake Game Help

    - by MuhammadA
    I am making a snake game and learning XNA at the same time. I have 3 classes : Game.cs, Snake.cs and Apple.cs My problem is more of a conceptual problem, I want to know which class is really responsible for ... detecting collision of snake head on apple/itself/wall? which class should increase the snakes speed, size? It seems to me that however much I try and put the snake stuff into snake.cs that game.cs has to know a lot about the snake, like : -- I want to increase the score depending on size of snake, the score variable is inside game.cs, which means now I have to ask the snake its size on every hit of the apple... seems a bit unclean all this highly coupled code. or -- I DO NOT want to place the apple under the snake... now the apple suddenly has to know about all the snake parts, my head hurts when I think of that. Maybe there should be some sort of AppleLayer.cs class that should know about the snake... Whats the best approach in such a simple scenario? Any tips welcome. Game.cs : using System; using System.Collections.Generic; using System.Linq; using Microsoft.Xna.Framework; using Microsoft.Xna.Framework.Audio; using Microsoft.Xna.Framework.Content; using Microsoft.Xna.Framework.GamerServices; using Microsoft.Xna.Framework.Graphics; using Microsoft.Xna.Framework.Input; using Microsoft.Xna.Framework.Media; using Microsoft.Xna.Framework.Design; namespace Snakez { public enum CurrentGameState { Playing, Paused, NotPlaying } public class Game1 : Microsoft.Xna.Framework.Game { private GraphicsDeviceManager _graphics; private SpriteBatch _spriteBatch; private readonly Color _niceGreenColour = new Color(167, 255, 124); private KeyboardState _oldKeyboardState; private SpriteFont _scoreFont; private SoundEffect _biteSound, _crashSound; private Vector2 _scoreLocation = new Vector2(10, 10); private Apple _apple; private Snake _snake; private int _score = 0; private int _speed = 1; public Game1() { _graphics = new GraphicsDeviceManager(this); Content.RootDirectory = "Content"; } /// <summary> /// Allows the game to perform any initialization it needs to before starting to run. /// This is where it can query for any required services and load any non-graphic /// related content. Calling base.Initialize will enumerate through any components /// and initialize them as well. /// </summary> protected override void Initialize() { base.Initialize(); } /// <summary> /// LoadContent will be called once per game and is the place to load /// all of your content. /// </summary> protected override void LoadContent() { _spriteBatch = new SpriteBatch(GraphicsDevice); _scoreFont = Content.Load<SpriteFont>("Score"); _apple = new Apple(800, 480, Content.Load<Texture2D>("Apple")); _snake = new Snake(Content.Load<Texture2D>("BodyBlock")); _biteSound = Content.Load<SoundEffect>("Bite"); _crashSound = Content.Load<SoundEffect>("Crash"); } /// <summary> /// UnloadContent will be called once per game and is the place to unload /// all content. /// </summary> protected override void UnloadContent() { Content.Unload(); } /// <summary> /// Allows the game to run logic such as updating the world, /// checking for collisions, gathering input, and playing audio. /// </summary> /// <param name="gameTime">Provides a snapshot of timing values.</param> protected override void Update(GameTime gameTime) { KeyboardState newKeyboardState = Keyboard.GetState(); if (newKeyboardState.IsKeyDown(Keys.Escape)) { this.Exit(); // Allows the game to exit } else if (newKeyboardState.IsKeyDown(Keys.Up) && !_oldKeyboardState.IsKeyDown(Keys.Up)) { _snake.SetDirection(Direction.Up); } else if (newKeyboardState.IsKeyDown(Keys.Down) && !_oldKeyboardState.IsKeyDown(Keys.Down)) { _snake.SetDirection(Direction.Down); } else if (newKeyboardState.IsKeyDown(Keys.Left) && !_oldKeyboardState.IsKeyDown(Keys.Left)) { _snake.SetDirection(Direction.Left); } else if (newKeyboardState.IsKeyDown(Keys.Right) && !_oldKeyboardState.IsKeyDown(Keys.Right)) { _snake.SetDirection(Direction.Right); } _oldKeyboardState = newKeyboardState; _snake.Update(); if (_snake.IsEating(_apple)) { _biteSound.Play(); _score += 10; _apple.Place(); } base.Update(gameTime); } /// <summary> /// This is called when the game should draw itself. /// </summary> /// <param name="gameTime">Provides a snapshot of timing values.</param> protected override void Draw(GameTime gameTime) { GraphicsDevice.Clear(_niceGreenColour); float frameRate = 1 / (float)gameTime.ElapsedGameTime.TotalSeconds; _spriteBatch.Begin(); _spriteBatch.DrawString(_scoreFont, "Score : " + _score, _scoreLocation, Color.Red); _apple.Draw(_spriteBatch); _snake.Draw(_spriteBatch); _spriteBatch.End(); base.Draw(gameTime); } } } Snake.cs : using System; using System.Collections.Generic; using System.Linq; using System.Text; using Microsoft.Xna.Framework.Graphics; using Microsoft.Xna.Framework; namespace Snakez { public enum Direction { Up, Down, Left, Right } public class Snake { private List<Rectangle> _parts; private readonly Texture2D _bodyBlock; private readonly int _startX = 160; private readonly int _startY = 120; private int _moveDelay = 100; private DateTime _lastUpdatedAt; private Direction _direction; private Rectangle _lastTail; public Snake(Texture2D bodyBlock) { _bodyBlock = bodyBlock; _parts = new List<Rectangle>(); _parts.Add(new Rectangle(_startX, _startY, _bodyBlock.Width, _bodyBlock.Height)); _parts.Add(new Rectangle(_startX + bodyBlock.Width, _startY, _bodyBlock.Width, _bodyBlock.Height)); _parts.Add(new Rectangle(_startX + (bodyBlock.Width) * 2, _startY, _bodyBlock.Width, _bodyBlock.Height)); _parts.Add(new Rectangle(_startX + (bodyBlock.Width) * 3, _startY, _bodyBlock.Width, _bodyBlock.Height)); _direction = Direction.Right; _lastUpdatedAt = DateTime.Now; } public void Draw(SpriteBatch spriteBatch) { foreach (var p in _parts) { spriteBatch.Draw(_bodyBlock, new Vector2(p.X, p.Y), Color.White); } } public void Update() { if (DateTime.Now.Subtract(_lastUpdatedAt).TotalMilliseconds > _moveDelay) { //DateTime.Now.Ticks _lastTail = _parts.First(); _parts.Remove(_lastTail); /* add new head in right direction */ var lastHead = _parts.Last(); var newHead = new Rectangle(0, 0, _bodyBlock.Width, _bodyBlock.Height); switch (_direction) { case Direction.Up: newHead.X = lastHead.X; newHead.Y = lastHead.Y - _bodyBlock.Width; break; case Direction.Down: newHead.X = lastHead.X; newHead.Y = lastHead.Y + _bodyBlock.Width; break; case Direction.Left: newHead.X = lastHead.X - _bodyBlock.Width; newHead.Y = lastHead.Y; break; case Direction.Right: newHead.X = lastHead.X + _bodyBlock.Width; newHead.Y = lastHead.Y; break; } _parts.Add(newHead); _lastUpdatedAt = DateTime.Now; } } public void SetDirection(Direction newDirection) { if (_direction == Direction.Up && newDirection == Direction.Down) { return; } else if (_direction == Direction.Down && newDirection == Direction.Up) { return; } else if (_direction == Direction.Left && newDirection == Direction.Right) { return; } else if (_direction == Direction.Right && newDirection == Direction.Left) { return; } _direction = newDirection; } public bool IsEating(Apple apple) { if (_parts.Last().Intersects(apple.Location)) { GrowBiggerAndFaster(); return true; } return false; } private void GrowBiggerAndFaster() { _parts.Insert(0, _lastTail); _moveDelay -= (_moveDelay / 100)*2; } } } Apple.cs : using System; using System.Collections.Generic; using System.Linq; using System.Text; using Microsoft.Xna.Framework.Graphics; using Microsoft.Xna.Framework; namespace Snakez { public class Apple { private readonly int _maxWidth, _maxHeight; private readonly Texture2D _texture; private readonly Random random = new Random(); public Rectangle Location { get; private set; } public Apple(int screenWidth, int screenHeight, Texture2D texture) { _maxWidth = (screenWidth + 1) - texture.Width; _maxHeight = (screenHeight + 1) - texture.Height; _texture = texture; Place(); } public void Place() { Location = GetRandomLocation(_maxWidth, _maxHeight); } private Rectangle GetRandomLocation(int maxWidth, int maxHeight) { // x and y -- multiple of 20 int x = random.Next(1, maxWidth); var leftOver = x % 20; x = x - leftOver; int y = random.Next(1, maxHeight); leftOver = y % 20; y = y - leftOver; return new Rectangle(x, y, _texture.Width, _texture.Height); } public void Draw(SpriteBatch spriteBatch) { spriteBatch.Draw(_texture, Location, Color.White); } } }

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  • What are the pros and cons of public sector vs private sector software development? [closed]

    - by j.i.h.
    I'm currently considering a job working for my state of residence. However, besides the obvious drawback of far less compensation than I could get in the private sector, are there any other drawbacks? Are there any upsides to public work, besides helping society at large and benefits? My main concern is that if I work in the public sector, I might be stained with the perception that I "got along" in an uncompetitive environment. I have no idea if this would be the actual environment, but it seems to be the preconception about government work--unionized workers who are simply there because the union keeps them from being fired. So, does anyone have experience working for the government? Do you have experiences working with people transitioning from public to private sector?

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  • Should I pass an object into a constructor, or instantiate in class?

    - by Prisoner
    Consider these two examples: Passing an object to a constructor class ExampleA { private $config; public function __construct($config) { $this->config = $config; } } $config = new Config; $exampleA = new ExampleA($config); Instantiating a class class ExampleB { private $config; public function __construct() { $this->config = new Config; } } $exampleA = new ExampleA(); Which is the correct way to handle adding an object as a property? When should I use one over the other? Does unit testing affect what I should use?

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