C++ :: Virtual Functions And Polymorphism
May 2, 2014if we do a virtual functions(polymorphism) why we need re-declare the functions(when we create a new class derived from other)?
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C++ :: Overload Virtual Member Function In Polymorphism?
Nov 30, 2013I defined a virtual class and three other classes based on it. I want to use them like this:
int main() {
Dirichlet_t D;
Neumann_t N;
Cauchy_t C;
PDEBoundary_t * B1=& D;
PDEBoundary_t * B2=& N;
PDEBoundary_t * B3=& C;
[Code] .....
but I got two major errors
1: "object f abstract type is not allowed" error.-----why not?
2: "the derived class must implement the inherited pure virtual method"-----Did't I?
C++ :: Why CRTP Used Instead Of Virtual Functions
Jan 31, 2014I was reading about the CRTP, and I can't for the life of me understand it's advantages over virtual functions.
Unless you're coding embedded systems, and can't afford the few extra bytes for the vptr, or coding something requiring high-performance, where every nanosecond counts, I just don't see why the CRTP is so attractive. It just adds more text and forces every user class that wants to use the CRTP'd hierarchy to become a template class.
I tried implementing my Functor hierarchy with the CRTP instead of virtual functions...All it did was clutter my files with angle brackets and made the whole thing look very ugly.
C++ :: Cannot Change Virtual Functions From Object?
Oct 14, 2013I try the functions pointers too, but without success. I understand the objects are the way for work with class's. until here fine. But why i can't change the virtual functions from an object? is there anyway for do it? Ican't do, outside of classfunctions, these code:
#include <iostream>
using namespace std;
class test {
public:
virtual void created(){};
[Code] ....
How i can validate these line:
void a::created()
???
C++ :: Using Virtual Functions In Base Classes
Oct 19, 2014I recall when I first started playing with C++ I was told that you should never use virtual functions unless you absolutely cannot think of a better way to do whatever you are attempting. This is something I have tried to stick to over the years - and indeed is probably why I have never used inheritance or polymorphism much in my own programmes.
However, I notice through a great deal of the code examples offered to questions here and even over on StackOverflow that commentators show no hesitation to recommend code that involves virtual functions. More so, I have even seen several instances here where - what I was taught as, but they may well have a different official name - 'pure virtual functions' (those with definitions inside a class of something like virtual int function_name(void)=0) are demonstrated and I was very clearly taught to avoid those like the plague.
I was wondering therefore has the official thinking changed since the middle nineties on when - and even whether - to use virtual functions in your programmes?
C++ :: Overriding Inherited Virtual Functions
Feb 15, 2013Is it possible to do something like this:
class A //parent {
public:
virtual void DoSomething() = 0;
};
class B : public A //child {
public:
void DoSomething(string s) override;
}
Where the child member function overrides and changes the parents member function.
I need to pass an array of key states to the Controller class' Update() function but don't want to send it to every class derived from Object (like Controller).
Is this possible or do I have to overload the original Update() member function (but I would need to define the method in Object then (i.e remove the pure virtual function (=0)))
C++ :: Pure Virtual Functions - Abstract Classes
Jan 26, 2013when I should use pure virtual functions.On the one hand, "TOY" for example should be an abstract class since theres no such thing as "TOY" , there are "toy cars", "toy fighters" etc , but on the other hand I need to force it somehow to be abstract since theres no really a function that any toy should have and implement on his own way (except PRINT maybe).
when I should REALLY use pure virtual functions? And if I want to avoid people from creating TOY objects (for example), the only way is PURE virtual functions. right?
C++ :: Virtual Functions From 2 Separate Base Classes?
Sep 11, 2014So I have 2 seperate base classes, (note that I removed the variables and functions that do not relate to the topic) Object.h
class Object{
public:
Object();
~Object();
[Code].....
The error I get is saying I am calling a function declared with one calling convention with a function pointer declared with a different calling convention and this makes perfect sense because for some reason, the function pointer is pointed at the virtual function Object::update but I can't figure out why and how to make it point at the virtual function Drawable::getImage.
Also, the virtual update function is called in a different place just before this and works correctly.
C++ :: Overloading Output Stream And Pure Virtual Functions?
Aug 7, 2013I'm working with inheritance and pure virtual functions, and I want to overload an output stream operator. However, every time I run the program I get this: 0x7fff00ee98c0.
I'll include a base class and a derived class so you can see what I'm talking about.
Base:
#include <iostream>
using namespace std;
#ifndef _Insurance_h_
#define _Insurance_h_
[Code]....
The application is something like this (I'm assuming the user has already inputted the name, salesperson, make, model, etc):
#include "Auto.h"
#include <iostream>
using namespace std;
#include <vector>
vector<Insurance *> sales;
[Code] .....
C++ :: Virtual Functions - Calculate Carbon Footprint For Car / Building And Bicycle
Apr 13, 2014I'm writing a program that calculate the carbon footprint for car, building, and bicycle. i have three classes building, car, bicycle. class called carbonfootprint have the pure virtual and should have the formula, but i didn't find it. having a little bit hard understanding some requests. like,
• Write an abstract class CarbonFootprint with only a pure virtual getCarbonFootprint method. Have each of your classes inherit from that abstract class and implement the getCarbonFootprint method to calculate an appropriate carbon footprint for that class.
• The main() function in the given program creates objects of each of the three classes, places pointers to those objects in a vector of CarbonFootprint pointers. You need to iterate through the vector, polymorphically invoking each object’s getCarbonFootprint method.
// Test program for CarbonFootprint and implementing classes.
#include <iostream>
#include <vector>
using namespace std;
int main() {
vector< CarbonFootprint* > list;
// add elements to list
[Code] ....
C++ :: Size Of Derived Class With Overriding Virtual Functions From Base Class?
Jan 21, 2014The compiler creates virtual table for the base class and also for the derived class whether we override it or not.
That means each class has separate virtual table. when we get the size of the each class with out any data members... the size of base is -- 4 bytes(64 bit) and the size of derived is -- 1
The size of base class 4 is correct since it creates the virtual pointer internally and its size is member data + virtual pointer, but it in this case I have included any data members so it has given 4 byts.
But why in case of derived is 1 byte, since it the derived class has overridden the virtual function from base, this will also contains the virtual pointer which will be pointing to derived class Vtable, it the size of the class suppose to be 4 instead of 1 byte.
#include<iostream>
class A{
public:
[Code].....
C++ :: Why It Is Runtime Polymorphism
Apr 4, 2013class Base
{
.....
.....
.....
virtual void display();
[code]....
in the above polymorphism why is it called runtime polymorphism when i can say seeing the code itself that display() function in derived gets executed with ptr->display(),so how does it become runtime polymorphism when i could get decide at compile itself ???
C++ :: Calculate Tax Of Vehicle With Polymorphism?
Dec 29, 2012How can we calculate tax of vehicle with polymorphism? There are 3 types of vehicles: long, commercial, and private vehicles' classes. There is a common class about all vehicles.
BASE class:
1.Brand and series name (such as Toyota Corrolla, Isuzu etc.)
2.Year of production (you can term it model)
3.Engine size in dm3
4.Owner’s name (including surname) and identity
5.Plate number.
COMMERCİAL :
1.Number of seats (apart from the driver)
2.Data to indicate whether the commercial vehicle is allowed to operate at night.
LONG :
1.The tonnage (max load in tons)
2.Data to indicate whether the long vehicle is allowed to carry goods internationally.
PRİVATE:
1.The class label which can be one of {A,B,C} .
C# :: How To Use Encapsulation / Polymorphism And Inheritance In WPF
Oct 20, 2014I have been reading up about object oriented programming recently and have come across 'Encapsulation, Polymorphism and Inheritance' as i understand it so far all OOP programs should use these three concepts. So i started thinking how do i get these concepts into my program as i am using WPF C# and i could not really find much good info about how these concepts apply to WPF programs.
Or do these concepts just not work with WPF programs?
C++ :: Does Polymorphism Affects Operators Overloading?
Nov 24, 2013I must overload [] but at the same time I must use polymorphism. I wonder if using polymorphism affects operators overloading since when I modified the first class by writing "virtual":
virtual void mostrarDatos(char*, char*, char*);
virtual void calcularEdad(int);
So I can do the polymorphism, it affects the part of the code where suppose to do an addition:
s=student1+=student2;
t=student3+=student4;
u=s+=t;
if I do that, it shows some strange numbers instead of the right ones. Here is the complete code:
.h
#ifndef PERSON_H
#define PERSON_H
#include <iostream>
using namespace std;
class persona {
[Code] ......
C# :: Inheritance Or Base Class / Polymorphism?
Sep 16, 2014I have couple of objects which are using some amount of methods. Right now my application is not OOP and i am going to transfer it to OOP. So i would create each class for my each object. Almost all methods are in use for each object, the only one thing which is changing some of those objects passing not all parameters inside specific method. I can go two ways one is prepare interface for all methods i got and each of my classes could implement its own definition for it but other way almost all would implement exactly the same methods but with different parameters so maybe its better to create base class then for each object do inheritance from base class (polymorphism). inside base class i can prepare base methods and classes which will inherit from that class would override those methods for requirements they want.
So imagine: You got:
Memory
CPU
Latency
and all of them using mostly all of those same methods (only arguments for one of them could be use different way):
ExecuteQuery()
ExportToExcel()
PopulateDataTable()
PutValueToReport()
Now its better to do like this e.g:
Base class: Stuff
prop: name, id, date ...
methods to ovveride: ExecuteQuery(), ExportToExcel() ...
classes: CPU, Memory, Latency (inheriting from Stuff)
ovveride methods and align its definition for specific class use (remember mostly only passing args are used or not by specific class)
or go with inheritance
Interface SomeMethods
ExecuteQuery()
ExportToExcel()
PopulateDataTable()
PutValueToReport()
and each class would implemet its own definition.
The most important thing is that those every objects mostly using all of those methods and what is diffrence that one object can use all of available parameters inside this method and other one no. What i should do? Go with interface or inheritance and polymporfizm inside base class?
C/C++ :: Use Virtual Function In Class In Which Virtual Function Is Defined?
Dec 27, 2012class Parent{
public:
virtual int width();
virtual int height();
int area(){return width()*height();};
[Code] ....
C++ :: Shape Class Polymorphism Compiler Error
Dec 10, 2014Having issues with program to create a shape area calculator with circle square and rectangle. the uml goes as follows:
Where the UML has shape as the abstract class with public area():double, getName():string,and getDimensions:string, rectangle derived from shape with protected height, and width, and a public rectangle(h:double, w:double), followed by a derived square from rectangle with just a public square(h:double), and finally a circle derived from shape with a private radius, and a public circle(r:double).
[URL]
Have linked my program and it is giving me the following compiler errors:
error: 'qdebug' was not declared in this scope line 15 of main
error: cannot declare variable 'shp' to be of abstract type 'shape' line 22 of main
error: expected primary-expression before ')' token lines 29 -31 of main
(note previously had qstring as a header file yet changed to string since I was getting error qstring was not declared in this scope.)
C/C++ :: Polymorphism Is Stopping Short Of Desired Class
Mar 2, 2014I've been working on this project which inserts data for different types of books lately, and I'm trying to utilize inheritance and polymorphism. The issue I've been having is after I create an object with my MediaFactory, I go to insert data into that type of object, but it won't reach the correct child class. The parent class in this case is MediaData. The class I'm trying to reach is Childrens, and the class that falls in between is called Book. The function I'm calling to insert the information is setData(ifstream&). This function simply places the information from a txt file into an object with the insertion operator.
Right now the program runs into the setData function of Book instead of Childrens. I need Childrens so I can enter all the required attributes (title,author,year). The call to this function is in MediaManager through the function called buildMedia, and my test is running into the case if (type == 'Y'). From there a pointer of type MediaData is created and pointed to a new object returned of type Childrens. I'm using my debugger in Xcode which does show that the correct object type (Childrens) was created.
I've tried a couple things so far. First I created another function called getData. From there I passed in *media and infile (txt input file) into that function, which then passed it right into setData with a pointer to the object and infile in the parameter. That didn't work, so I also tried going back into Childrens and removing MediaData from all my virtual functions and replacing it with Book. I got the same result when that happened; It morphed into Book class instead.
I have a portion of my UML as a reference. Childrens is a Book; Book is a MediaData. I also included all code for MediaManager, MediaHash, MediaFactory, MediaData, Book, and Childrens.
I did not include the operator overloads in the .cpp files to eliminate some redundancy.
//-----------------------------------------------------------------------------
// MediaManager.h
// Manager class for MediaData type objects
//-----------------------------------------------------------------------------
#ifndef MediaManager_H
#define MediaManager_H
#include "MediaHash.h"
#include "MediaFactory.h"
#include "MediaData.h"
using namespace std;
class MediaManager {
[Code] ....
C++ :: Polymorphism On Class Instance Is Not Directly Applicable To Array
Mar 19, 2013Below code produces run-time segmentation fault (core dumped) when execution reached line 53: delete [] array
Code 1:
#include <cstdlib>
#include <iostream>
using namespace std;
#define QUANTITY 5
class Parent {
protected:
int ID;
[Code] ....
Output of code 1:
Constructor of A: Instance created with ID=1804289383
Constructor of A: Instance created with ID=846930886
Constructor of A: Instance created with ID=1681692777
Constructor of A: Instance created with ID=1714636915
Constructor of A: Instance created with ID=1957747793
A::showID() -- ID is 1804289383
A::showID() -- ID is 846930886
A::showID() -- ID is 1681692777
A::showID() -- ID is 1714636915
A::showID() -- ID is 1957747793
Try to delete [] array..
Segmentation fault (core dumped)
Question: Why does segmentation fault happen in code 1 above?
C++ :: basic Polymorphism - Parent / Child Class Based Program
Oct 19, 2014I am making a very basic parent/child class based program that shows polymorphism. It does not compile due to a few syntax errors reading "function call missing argument list. Lines 76 and 77, 81 and 82, and 86 and 87.
#include<iostream>
using namespace std;
class people {
public:
virtual void height(double h) = 0;
virtual void weight(double w) = 0;
[Code] ....
C/C++ :: How To Access Linked List Functions From Stack Class Without Functions
Mar 20, 2014I'm a little confused by my programming assignment this week. I've been working at it Wednesday and I've made progress but I'm still confused as to how I'm supposed to do this. The class I made is called Stack, and it's derived from a template class called StackADT. We also utilize a class called unorderedLinkedList, which is derived from a class called linkedList.
We're supposed to implement all of the virtual functions from stackADT in the Stack class. The Stack data is stored in a an unorderedLinkedList, so what I'm confused by is how to implement a few of the Stack functions because there are no functions in unorderedLinkedList which we could call to manipulate the data.
As you can see from my attached code, I'm really confused by how I'm supposed to implement the pop() and top() functions, and I also think my initializeList() function is wrong. We don't have any similar functions in unorderedLinkedList to call, so I'm at a loss of how i'd access my unorderedLinkedList. My initial thought was to call the similar functions in the class that unorderedLinkedList was derived from, linkedList, but I'm unsure of this is what we're supposed to do, or if theres actually a way to access my unorderedLinkedList without having to use the functions from the base class.
NOTE: We're not allowed to modify stackADT, unorderedLinkedList, and linkedList.
Stack.h
#include "stackADT.h"
#include "unorderedLinkedList.h"
template<class Type>
class Stack: public stackADT<Type>{
template <class T>
struct nodeType
{
T info;
nodeType<T> *link;
[Code]...
C/C++ :: Array Of Functions Pointing To In Class Functions With Arduino
May 3, 2013At the moment im trying out with pointing to an array of functions. I got this working as following:
typedef void (* functionPtr) ();
functionPtr functions[2][2]={{do11,do12}, {do21,do22}};
void do11(){DEBUG_PRINTLN("11");}
void do12(){DEBUG_PRINTLN("12");}
void do21(){DEBUG_PRINTLN("21");}
void do22(){DEBUG_PRINTLN("22");}
void loop(){
A=0;
B=1;
functions[A][b]();
}
But now I'm trying to use this to point to a function inside a class so instead of do11, i want to be able to point to Basic.Do11. Somehow this doesnt work and I keep on getting this message:
error: argument of type 'void (Basic::)()' does not match 'void (*)()'
C++ :: Virtual Methods With MI
Jan 6, 2014I have questions about multiple inheritance and virtual methods. I have a class called solid. All objects of this class have hitboxes and can collide with others. I have the following methods:
void testCollision(something begin, something end);
/* This method takes a container's begin and end iterators to test if the object collides with any other object of the list of all the solids currently in the game area. Each time there is a collision, it calls collide(other) and other.collide(*this) */
virtual bool collide(solid& other);
/* This method always returns false and does nothing */
This class will be inherited by another class which will have overloads for a few specific collisions. For example:
class player : public solid{
public:
bool collide(projectile& other);
bool collide(enemy& other);
bool collide(wall& other);
};
My question is quite simple actually. If I have a loop which calls testCollision() with all elements in the list of all solids (a list of pointers to solids to be exact) and there is a collision between the player and a projectile, will testCollision call player::colide(projectile& other) or will it call solid::collide(solid& other). And in any case, did I understand how to use the virtual keyword? If I'm right, it should call the player::colide method if it's there for the specific type, else it will call the solid::colide which only returns 0, ignoring collision.
C++ :: Use Of Virtual Keyword In Destructors
Jan 6, 2014have a look at the following code :
class Base
{
public:
virtual ~Base()
{
cout << "Calling ~Base()" << endl;
[Code]...
Now this program produces the following result:
Calling ~Derived()
Calling ~Base()
i was reading online and got stuck here. i am unable to understand why 'calling ~Base()' is been printed here? when we reached delete pbase; in int main() it goes to Base class first and finds that its destructor is virtual so it goes to Derive class and finds another destructor and executes it but why does it prints ~Base() in any case?
C++ :: Using Reference With Virtual Method
Mar 19, 2013#include <iostream>
using namespace std;
struct A {
virtual void f() { cout<<"A
"; }
};
[code]...
I would expect that both examples 2 & 3 will give me the same result.I tried to figure it out but I could not. Both are references of a base class type, that get a derived object.
Q1 : why is the difference between them ?
As I see it, its kind of a mix between pointer - which in case of virtual method that was override in derived class - would give me the derived method (e.g. "B") and between regular object - which in case of virtual method that was override - would give me the specific method (Still "B"). So, example 2 "use" it as a regular object and example 3, "use" it as pointer.
Q2 : How should I refer to it ? I am using VS2008.