How to create a dynamic array of an Abstract class?

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Lets say I have an abstract class Cat that has a few concrete subclasses Wildcat, Housecat, etc.

I want my array to be able to store pointers to a type of cat without knowing which kind it really is.

When I try to dynamically allocate an array of Cat, it doesn't seem to be working.

Cat* catArray = new Cat[200];

By creating an aray of pointers to Cat, as in

 Cat** catArray = new Cat*[200];

Now you can put your WildCat, HouseCat etc instances at various locations in the array for example

 catArray[0] = new WildCat();
 catArray[1] = new HouseCat();
 catArray[0]->catchMice(); 
 catArray[1]->catchMice();

Couple of caveats, when done a) Don't forget deleting the instances allocated in catArray as in delete catArray[0] etc. b) Don't forget to delete the catArray itself using

 delete [] catArray;

You should also consider using vector to automate b) for you

C++ How do I create a dynamic array of objects inherited from an , Firstly main must return int . Then you need to create an array of pointers which will show to abstract class Figure . Figure **dyn_arr = new Figure*[size]; Then if you want to add a new object of the derived class you are adding simply like this. 4 Answers4. You cannot create instances of abstract classes, but you can assign concrete derived instances to pointers or references of the base class. You need reference semantics for that, because Food arr [2]; tries to initialize the array with default values (which are abstract, thus not constructible).

You would need to create an array of pointers to Cat:

Cat** catArray = new Cat*[200];

Even if the base class Cat was concrete, you would still run headlong into object slicing if you created an array of Cat.

Note that you should probably use a std::vector instead of an array, and should probably use smart pointers to ensure your code is exception safe.

Creating a dynamic array of an abstract class, Just replace class Cell2 : CellPhone by class Cell2 : public CellPhone . Else, conversion from Cell2 to CellPhone is not accessible (inheritance is private if  I need to create an array of an abstract class, actually its not really an abstract class, it is actually a struct but it is an abstract class because structs and classes

You cannot round up the cats in fixed size cages, because the compiler has no way of knowing how big the cats will be, nor (metaphor failure) how to initialize them. You are going need to do something like initialize the array to null cat-pointers or something, and herd them later.

how to create array of an abstract class in c++, You cannot create instances of abstract classes, but you can assign concrete derived instances to pointers or references of the base class. vector<Parent> planes; doesn't make sense because a Parent can't exist. It's an abstract class. You can have a vector of pointers or, better yet, smart pointers. Even if Parent wasn't abstract, the vector of Parent objects would suffer from object slicing and it's probably not what you want, since it would break polymorphism.

You cannot directly instantiate an instance of an abstract class, but must instead instantiate an instance of a fully implemented subclass.

So this is legal:

Housecat* theCats = new Housecat[200];

and then you can access each cat through the Cat interface

bool catsMeow = ((Cat*)(&theCats[0]))->CanMeow();

But the compiler has no way of knowing how to instantiate an abstract class; in fact, the very fact that it's abstract means that it cannot be directly instantiated.

Why do this? Because Cat will have an abstract method

bool CanMeow() = 0;

That all inherited cats must implement. Then you can ask if it can meow, with the chance that an instance of Lion will return false.

Creating arrays of object of abstract class in statically-typed object , In statically-typed object oriented languages (like Java), you can not create an object of an abstract class. Abstract classes are (usually) not completely defined,​  What you can create is a reference to an object instance of an abstract class. A reference is just a pointer to an object, not the object itself. myclass1 arr [] = new myclass1 ; Creates an array of 10 null references to objects of class myclass1.

Something I did in a similar case was then to loop through the array and point each element to nullptr. That way you can easily check whether you've added a derived class object to a slot or if it's open.

Cat** catArray = new Cat*[200];
for(int i = 0; i < 200; i++){
   catArray[i] = nullptr;
}

for(int i = 0; i < 200; i++){
   if(catArray[i] != nullptr){
      AddRealCat(...);
      break;
   }
}      

I wonder if there's an easier way to do this, to check whether an element in an array of pointers to an abstract class points to an object of a derived class or is just an abstract pointer, without setting the element to nullptr. Like, is there a bool IsObject(ObjectType* ptr) or something in the standard library?

And, I wonder if setting each element to nullptr poses any potential problems, other than the computing cost of looping through the array and setting them to nullptr.

I posted this as an independent question (Array of Pointers to an Abstract Class: to nullptr or not to nullptr (C++)), but I thought it might be relevant here since this post is the closest to my question that I found when searching.

Dynamic array of abstract objects - C++ Forum, The case is I have an abstract class Element, and two derivated class Circle and Square. What I would like to do is store in an array both Circle  Abstract Class as name implies can't be instantiated. When you did Game[] gamesArray = new Game[10]; it is creating an array which can hold Game references. Lets try to relate it to a real life scenario. Say you have an abstract class Animal. You can't instantiate it as animal is not a concrete class so Animal obj = new Animal() would fail.

[PDF] A C++ DYNAMIC ARRAY The constructor The destructor The , First we define the required functions and operations: class Dynarray { private: int *pa;. // points to the array int length;. Translating a character array into a integer string in C++. c++,arrays,string. If you want a sequence of int, then use a vector<int>. Using the key_char string, the values of the chars in it will serve as the initial value of the ints. std::vector<int> key_num(key_char.begin(), key_char.end()); Then, iterate over each character of key_num and convert it to the equivalent int value for

How to create an array of an abstract class in C++? - MSDN, I need to create an array of an abstract class, actually its not really an abstract class, it is actually a struct but it is an abstract class because  This article provides example of dynamic array implementation using C++ templates. It uses standard malloc/realloc memory allocation functions and simple "doubling size" resizing strategy. Our AeDynArray class interface resembles MFC standard CArray class, but uses only standard C libraries.

Virtual Functions and Abstract Classes, One solution, of course, would be to create a separate array for each subtype. new Grad; // dynamic Grad object // we can continue adding items to the array,  Note: Although abstract classes cannot be used to instantiate objects, they can be used to create object references, because Java’s approach to run-time polymorphism is implemented through the use of super-class references. Thus, it must be possible to create a reference to an abstract class so that it can be used to point to a subclass object.

Comments
  • Actually, there seems to be a memory size mismatch. Working on figuring that out.