C++ :: Singleton Design Pattern - Why Copy Constructor Not Made As Private
Jul 9, 2014
I was going through Singleton design pattern and get to know that objects can be created only by static function of that class and constructors are make private.
My question is, why assignment operators are not made private through which we can create a copy of already existing object.
I tried below code and assignment works, so I have new object sc3. I know that its referring to memory of sc1 but finally I was able to create object without using static function.
Also, why copy constructor not made as private.
Below is code:
#include <iostream>
using namespace std;
class Singleton {
private:
static bool instanceFlag;
#include <stdio.h> #include <stdlib.h> #include <iostream> using namespace std; class singleTon {
[Code] ....
this is a singleton pattern first,it doesn't matter, why I could delete this pointer twice?because the gcc compiler?That mean in the surface, "delete pInstance1;" this movement just mark the memory pInstance1 has been deleted but not real?does any one encounter this phenomenon?
I need to design an interface(a function prototype) that takes an argument which is used to pass information. The information can be passed by independent modules and third party softwares and hence can vary today and in future.
Basically, the function interface(arg1, info)caters a niche service to many independent applications and needs to process based on requirements passed by applications in the argument(info, in example).
I am looking for a design pattern for the function parameter - info.
Should I use a void pointer that can be casted to respective application specific class in the function ? will this be a good C++ design ?
or should I take this parameter to be a pointer to a generic abstract class that points to the respective application specific specialization ?
Do we have some design pattern to address this so as to handle other unforeseen challenges ?
I need to design an interface(a function prototype) that takes an argument which is used to pass information.
The information can be passed by independent modules and third party softwares and hence can vary today and in future.
Basically, the function interface(arg1, info) caters a niche service to many independent applications and needs to process based on requirements passed by applications in the argument(info, in example).
I am looking for a design pattern for the function parameter - info.
Should I use a void pointer that can be casted to respective application specific class in the function ? will this be a good C++ design ?
or should I take this parameter to be a pointer to a generic abstract class that points to the respective application specific specialization ?
Do we have some design pattern to address this so as to handle other unforeseen challenges ?
In the following code example of the State Design Pattern, in the main code at the bottom it defines an instance of class Machine, and then calls Machine::off;. Why doesn't it instead call fsm.off;?
Machine fsm;
Machine::off;
Then I tried imitating that by adding a class Abba, and then doing:
Abba a; Abba::DoStuff();
but that didn't work. Why?
Full code example:
// StatePattern.cpp : Defines the entry point for the console application. //
#include "stdafx.h" #include <iostream> using namespace std; class Machine { class State *current;
I'm building a Windows Form Application using MVP Design Pattern; the application is quite simple, it just calculates the sum of two number; So I have a form in which are located tree textbox: number1 number2 and result, plus a button to perform the action.
For now I've done a function that creates menus and prints them, and a function that creates the character as an object.
Now I want to be able to show the stats of the player on the main menu, the problem is that I don't know how to make a copy of the map as it's private...
The following are the cases when copy constructor is called.
1)When instantiating one object and initializing it with values from another object. 2)When passing an object by value. 3)When an object is returned from a function by value.
I don't understand #2 How can and object be passed by value? when I think of passing object I think of passing by address or reference. explain
I don't understand #3 how can a function returned object by value I think of again passing by address or reference.
copy constructor. I'm not really understanding them. I have a base class called Vehicle and a derived class called Car.
class Vehicle { private: int age;
[Code].....
I'm trying to test the new attributes and behavior of car but I think its not working because of the copy constructor. Its just not clicking. I also forgot that race car status is supposed to return yes or no, am I defining that right?
I was wondering that why in the below code, the copy constructor is called 2 times.
Code: class A { private: static int count; int age; public: A()
[code].....
I think that when f(a) is called, since I am passing this as value, no copy constructor should be called. The copy constructor should called when the return object "x" is assigned to:
I can't find why it won't output the correct info for the array. I've looked until I am ready to throw the computer out the door. I'm at my wits end trying to get this to work right. I finally got it to quit killing the compiler, but it's doing this. The problem is in the insertBefore or insertAfter function calls and I don't think that my copy constructor is right.
How do i write main test program to test the copy constructor and assignment operator in this program...how do i know if its working as its suppose to?i just want to know about copy and assignment operator..i have figured out the test program for other things..Here my program :
I've been working on some project and I got to wondering when you know you need to use a copy constructor and an assignment operator. Is there a rule of thumb? I know there is the Rule of Three, but is there something that tells you when you need those three?
I have problems to put a list inside a linked list. I have the following conditions to fulfill:
- main.cpp can NOT be changed - There must be an abstract base class 'shape' - Methods such as area() and print() must be in code - Constructors is as follow:
Point( double x, double y, double size) Circle( double x, double y, double radie) Rectangle( double x, double y, double width, double height) Polygon( double x, double y, Vertex *varr, int num)
List::List(const List& list) { if ( list.empty() )
[Code].....
I think I'm not really able to track the new node for this reason my app crashes.
ListNode* p = list._pFront ; this is for the original node p ->_data;
the data inside the original node. Each node has three pointers. One for the entire node which tracks whether the node in front or in the back. The other two for next and previous nodes.
I know everything works except my copy constructor! There are no errors. The program crashes when it goes to access the copy constructor. why the copy constructor isn't working?
#ifdef _MSC_VER #define _CRT_SECURE_NO_WARNINGS #endif #include <cstring> // access to C str functions #include "String.h" // access String class using namespace std; String::String( int size )// default constructor
I'm working on a project and I'm not quite sure how to implement the Copy constructor and Overloaded assignment operator.
This is what the instructions say if that matters at all: Since you have dynamic variables in your class, you should make sure that the big three are implements. You already have the destructor, but you will need to add a copy constructor and the overloaded assignment operator. This is simpler than it sounds, but it requires some thinking. You need to make sure that both the copy constructor and the assignment operator create new containers.
