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vector of objects vs vector of pointers

Store pointers to your objects in a vector instead of copies of the objects themselves. I have a class that has a std::vector of pointers, I'm NOT going to give any of those pointers to objects outside of it, I mean, I'm not going to share the pointers. This is a bad design at any rate, because the vector can internally make copies of the stored objects, so pointers to those objects will be invalidated on a regular basis. The object type is not the issue, but the fact that when you 'erase' an elements from a vector, any iterators pointing to it or any elements after it (i.e. May be, using vector<Person> (not vector<Person*>) is the best (safe) variant, but you may use vector<Person*> too - for example: Of course one can use First of all, you might want to see the sidebar for advice on asking a question. it is possible to change the values of double s through an iterator-to-const: Listing 1: Behavior of a std::vector for pointers. Hi guys, I have a vector that is holding pointers to 7 objects, but my destructor does a single delete and stops. Pointers: A pointer is a variable that holds memory address of another variable. Is anyone working on a compiler that can essentially rewrite user defined structs, and loops that touch them, into code that has far better memory access patterns? To use a C++ vector, program has to include vector library with a directive. For small arrays and small number of updates/calls there is almost no difference. vector of shared pointers is around 8% slower (for 1000 of objects), but for larger number of objects in a container we can loose like 25%. The approach of overloading the < operator of the class wouldn't work in this case. That's why you'd want to use a smart pointer. // Initialize vector with 5 integers // Default value of all 5 ints will be 0. Check it out here: C++20: Heterogeneous Lookup in (Un)ordered Containers, 6 More Ways to Refactor new/delete into unique ptr. Basically I’ve created simple Vector of objects needs 5ms to allocate 50k though. stores pointers to moviedata objects. Even live debugging it just gets stuck at the first delete. shared pointers! The reason for the const_iterator, is to apply the constness of the vector to the elements. IIRC, vector has two functions: size, that tells the number of elements stored in vector capacity, that shows how much memory has been reserved; If the vector doesn't have to be sorted then you can minimize copying by moving the last element to replace the deleted one in the middle of vector. Why doesn't that work? I try to write complete and accurate articles, but the web-site will not be liable for any errors, omissions, or delays in this information or any losses, injuries, or damages arising from its display or use. After watching some of the talks from Build Vector iterators are used to point to the memory address of a vector element. Vector usually deals with primitive data types like int, string, double. However, there would be complexities and overhead arising when dealing with vector of class objects. I'd suggest you to work with myObject rather than vector iterators. For efficiency or other reasons, you can't store copies of your objects in a vector, but you need to keep track of them somehow.. It seems the compiler treats the adress as a pointer to an adress (*& - or the adress of a pointer?? A pointer needs to be dereferenced with * operator to access the memory location it points to. I wanted to create a class that contains Please notice that the above code was enhanced with randomize section. some talks from Eric For 50k of elements we spend 20ms on allocating memory for That means the pointer you are saving is not a pointer to the object inside the vector. Alternatively, we can use the void * pointer if you require a generic address type to store opaque data structures or, on the contrary, use a pointer to a custom . Feb 27 '17 at 9:03. Computer Programming If your object is large, then the wasted capacity may not be a large fraction of the memory usage. I have a Board object which holds a paddle, a ball, and a vector of Bricks (the stuff you're meant to get rid of). Built on the Hugo Platform! typedef iterator pointer; vector<bool>::reference Class. In this article, we will discuss vector of pointers to objects. For efficiency or other reasons, you can't store copies of your objects in a vector, but you need to keep track of them somehow.. Sorting a vector of pointers to objects using STL and functors. Because the Vector stores pointers to the objects, and not the objects themselves, these Vector items could be any kind of object. Moreover, several different kinds of objects could exist in the same Vector. I've prepared a valuable bonus if you're interested in Modern C++! The destructor of std::vector cleans up whatever allocations were made by the std::vector object itself, but it will not clean up the allocation that you made when you allocated a Foo object, even though you put a pointer to that allocated Foo object into the std::vector object. ensures pointers, references and iterators will never be invalidated while the object is live, even on swap() vector may invalidate pointers and iterators when you have a reallocation: has no pointers, iterators, so you can only invalidate it by swap: Compatibility with concepts and algorithms: is a regular container: is a regular container This site contains ads or referral links, which provide me with a commission. Having vector of objects is much slower than a vector of pointers. The approach of overloading the < operator of the class wouldn't work in this case. Initializing a vector with default value of elements. However, if a programmer, who cares about this sort of optimisation, cannot make assumptions about it anymore, then it’ll only induce headaches. Oh please no. 0 Comment. So if. Also, the iterator is a local object created on stack and hence returning the address of the same is not at all safe. int row; int col; double len; bool operator < (Line_info* param) That means the pointer you are saving is not a pointer to the object inside the vector. Download a free copy of C++20/C++17 Ref Cards! 1) std::vector is a sequence container that encapsulates dynamic size arrays. The vector<bool>::reference class is a proxy class provided by the vector<bool> Class to simulate bool&. - I was reading that isn't everywhere that we will use smart pointers and that raw pointer isn't useless as long that someone is responsible for deleting it. You definitely do not want a vector of object. For example, what will be output of below C++ program. I want to sort the objects based on the len member. Example 6-4 shows how to declare and work with . The binary search and sort are also upgraded to reflect the new data structure. A type that describes an object that can serve as a pointer to a Boolean element of the sequence contained by the vector<bool> object. Vector of Pointers. Classes Brick and Ball derive publicly from class Object, because I have a polymorphic function to check colissions between 2 objects (Ball object is sf::CircleShape and Brick object is sf::RectangleShape). This code creates a fragmentation in the memory. Vector of class objects in C++. Set ptr [i] to point to data [i]. Solution. Problem. class object { //Attributes of object object * other_object_to_interact_with; std::vector<object*> carried_objects //etc } I've now realised that changing the size of the vector (a frequent occurrence in this simulation) causes all pointers to elements within that vector to point to some random piece of memory. New comments cannot be posted and votes cannot be cast. Once again: repository can be found here: Press question mark to learn the rest of the keyboard shortcuts. code that compares vector vs vector> The first results are quite interesting so I thought it is worth to describe this The results are because algorithms such as sorting need to move elements inside the container. Object can be a class object or structure object. What problem do you see? Vector of Pointers to Structure. Same as #2, but first sort the ptr array so that * ptr [i] <= * ptr [i+1]. Vector of Object pointers . If any of the destructed thread object is joinable and not joined then std::terminate() will be called from its destructor. To show how, we'll use the example from that post again. Not more unpredictable wise-assery from compilers. Obviously there is very good locality of access to both arrays. Sep 23, 2015 at 9:26am. one new to create the object before adding a pointer to the object to the vector, and one delete after removing the object from the vector, in order to avoid a memory-leak). Brumer I started Problem. Storing pointers in your vector is usually less efficient than storing the objects directly, for the following reasons:. As title says, I want to access a vector of objects, I got an accessor (getter) function getVector () that returns a shared_ptr of a vector of these objects, and I use it in another function addStuff (Obj obj) that takes said object and push_back into the vector pointer that . Please help! Solutions is a vector of CVRPSoltion objects and the comments are things that I've tried, including using a unique_ptr and trying to move the pointer. Vector provides a constructor that accepts the size as an argument and initialize the vector with that many objects of default value i.e. This changes the address of that object. C++ Vector of Object Pointers- Destructor not working. Usually i would just store raw pointers to Bricks in a vector, and just delete the brick when hit, and replace the index in the vector with a nullptr. Solution. Example 6-4 shows how to declare and work with . If you provide direct access to the container via an accessor then it's possible for anyone to modify it. This might be slower or not, depending on the object's definition. I have the following c++ function on MyClass: class MyClass { public: std::vector<MyObject*> getVector(); }; I want to make sure objects that grab this collection don't modify the colle. An iterator is more restricted, e.g., a vector::iterator can only refer to doubles that are inside a vector container. Vector of class objects in C++. It supports operators like ++ and --(both postfix and prefix), == and !=, addition of an int, subtraction with another iterator (which gives the distance between two iterators), and of course unary *, the dereference operator (i.e. some "safer vector" for pointers? Edit: Since you are inserting pointers in your array, the excess capacity will just be filled with NULL pointers. Thank you for your understanding. 1,315. By CPP_Programmer | August 10, 2020. In the copy process, the shared_ptr increases its so-called reference count, such that it knows when exactly to call delete. std:: vector. Or if the element type doesn't support moving very well. Theoretically possible, but not something anyone should want; there is no guarantee it’ll speed up the program and platform differences may yield very different results, hence cache–oblivious algorithms. A vector of pointers would be used in a totally different situations...like if you need other code to be able to store pointers to the elements and you don't want to worry about the vector resizing. typedef std::shared_ptr<nodes> NodesPtr; std::vector<NodesPtr> fringe; read-a-value).. Typing std:: vector< int >::iterator is annoying . It will be necessary for me to know what contacts a specific . This is a bad design at any rate, because the vector can internally make copies of the stored objects, so pointers to those objects will be invalidated on a regular basis. memory efficient code. Imagine you have a stl::vector container that contains pointers to objects of some class, and that you'd like to sort them based on the value of some member variable using a STL algorithm. on the blog. waits for the memory package to arrive. vector<vector<int> > *varVect; //this is the vector pointer that need to hold the other vectors vector<int> var; //i creates on loop this vector with values //and every time its full i need to insert it to the array of vectors: the vector<int> var works fine,after i insert values i print it and its ok You can use the PImpl idiom to avoid this, you have a concrete Enemy class that holds a (unique) pointer to a concrete enemy an abstract IEnemy that holds the custom code. As a more concrete example I’ve used Particle class. If you really want the users of your class to be able to directly access that vector, and if the vector will always exist, consider returning it by reference. Full repository can be found here: vector<T>::iterator iteratorName; For example, if we have 2 vectors of int and double types, then we will need 2 different iterators corresponding to their types: A pointer of type T* can point to any type T object. References : A reference variable is an alias, that is, another name for an already existing variable. I need to finalize the code and maybe do some basic optimizations. initialize vector of pointers c++. Imagine you have a stl::vector container that contains pointers to objects of some class, and that you'd like to sort them based on the value of some member variable using a STL algorithm. Accessing any element of the Base* vector results in an invalid pointer. The memory adress at Enemies.at(i) is correct, but I can't seem pass to adress the way I want. From what you've described, getVector()->push_back(obj) sounds right. I can solve this by making the first vector also a vector of pointers (std::vector<Derived*>). We can delete a pointer using delete: Since an iterator refers to objects in a container, unlike pointers, there's no concept of delete for an iterator. {. This lab upgrades the movie data assignment: structs are upgraded to classes/objects and arrays to vectors. EDIT: If the object is lightweight then its better you return the object itself. In some ways, they act like pointers in C++. wouldn't vector<obj> perform worse than vector<ptr<obj>> Probably. This method appends the given object to the end of the Vector. It returns a pointer to a new passenger and you may add it to the vector of pointers. Scan the data through the ptr array and compute the sum. Learn more about Reddit’s use of cookies. - I was reading that isn't everywhere that we will use smart pointers and that raw pointer isn't useless as long that someone is responsible for deleting it. By CPP_Programmer | August 10, 2020. Store pointers to your objects in a vector instead of copies of the objects themselves. I am writing an application using openFrameworks, but my question is not specific to just oF; rather, it is a general question about C++ vectors in general. 19.4 Movie Data - Vector of pointers to MovieData objects. We can create vector iterators with the syntax. A vector, like all other objects, is passed by value, so if you fail to pass it by reference or pass a pointer to it, then the function operates on a copy of the vector instead of the vector itself. But for vector of pointers this is not as straightforward, since memory management comes into play. vector<bool>::pointer. C++ wraps up the pointers in iterators, so all vector has two iterators.. Vector contains a pointer to the elements, so normally nothing prevents the modification. 1. fancy CPU instructions, but they will not do much when code basically Perhaps you should make the vectors fringe and TempFringe hold nodes pointers rather than nodes objects. Since the pointer types can be modified easily, we will use int * in the following examples to declare a vector of pointers. C++11 introduced std::unique_ptr along with other smart pointers, that wrap a normal pointer and takes care of memory management, by calling delete on the pointer in their destructors. (The container is . Here's another result when the size of a Particle object is increased to 128 bytes (previously it was 72 bytes): See the benchmark at @QuickBench. no difference. << Flexible particle system - Emitter and Generators, Flexible particle system - The Container >>. pointers, std::vector, and derived types and base classes from the boost documentation. The elements are stored contiguously, which means that elements can be accessed not only through iterators, but also using offsets to regular pointers to elements. You want vector of pointer. You Need to Know” and As Giovanni suggests, it would be better to use smart pointers rather than raw pointers. As title says, I want to access a vector of objects, I got an accessor(getter) function getVector() that returns a shared_ptr of a vector of these objects, and I use it in another function addStuff(Obj obj) that takes said object and push_back into the vector pointer that is being returned by the first function getVector(). But if you do, don't forget to delete the objects that are pointed to, because the vector won't do it for you. In my C++ project, I have three classes, Particle, Contact, and Network.The Network class will have N particles (std::vector<Particle> particles) and Nc contacts (std::vector<Contact> contacts).Particle objects will each have a number of contacts, represented by Contact objects, and contacts are shared by pairs of particles.. )It is rather important, that the combat class recieves the adresses of two vector<MonsterType> as arguments, but I am very open to suggestions. If you had memory allocation in these objects that was automatically deallocated when the destructor was called, that could explain . It wouldn't make sense to return the vector by value cause then the original vector wouldn't change. Programming languages like C allow the programmer to seek optimisations through the lens of memory and data access. 3. I need some help getting the standard library sort routine to work when I try to sort a vector of pointers to objects. This is like returning a const T* when the vector is const, and returning a T* when the vector is not const. venros. 2. std::vector<std::string> obs1; char * * obs2; Effectively, obs1 and obs2 are almost identical, but obs1 is massively simpler to use. the errors are no matching function for call to ‘std::vector::push_back(std::remove_reference::type)’ , and Invalid arguments ' Candidates are: void push_back(const CVRPSolution &) void push_back(CVRPSolution &&) '. Create an array of ints (data) and an array of int* (ptr). When the vector grows the memory can get reallocated. https://www.youtube.com/watch?v=ZHqFrNyLlpA, https://odin-lang.org/ also has #soa (can't find it in the documentation though).

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