C++ :: When A Copy Constructor Is Called
Apr 27, 2013
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.
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Sep 15, 2013
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:
A b = x;
why copy constructor called 2 times?
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Nov 19, 2012
#include<iostream>
using namespace std;
class Cents {
public:
int m_nCents;
Cents(int nCents=0):m_nCents(nCents){
cout<<"Calling normal constructor with value:"; m_nCents = nCents;
cout<<m_nCents<<endl;
[code].....
Question is :Why is the overloaded copy constructor that I have written not getting called here?Internally default copy constructor is getting called.Thats why we get value of obj2.m_nCents as 37.
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Apr 10, 2013
I have the following classes and 'dreaded diamond':
A
/
/
B C
/
/
D
|
|
E
Classes B & C both inherit from A using public virtual A.
E is the only concrete class. None of the classes are totally abstract.
Every class has a copy constructor.
All of the copy constructors are chained together through the initialization lists.
E correctly calls D's copy constructor.
D correctly calls B and C's copy constructors.
But neither B nor C call A's copy constructor, although A's default constructor is called. To reiterate B and C have a call to A's copy constructor in their initialization lists.
I guess A's default constructor is being called is because of virtual inheritence, but why isn't its copy constructor called (too)?
A's copy constructor includes some very important code and I could do with calling it. Should I call it from the concrete class' initialization list or is that considered bad form?
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Sep 17, 2013
Whenever my copy constructor is called, my destructor destroys is immediately after.
My copy constructor
CS1CStudent::CS1CStudent(const CS1CStudent& otherCS1CStudent)
{
cout << "
***************************
";
[Code]....
The copy constructor is called twice, once when you pass an object by value, and once when the object is returned from a function by value. But why is the destructor being called twice?
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May 17, 2013
When the below is done, does it call the constroctor only, and if yes, constructors do not have return types so how does it work? is there anything behind the scene?
wxAddHandler(new wxPNG_HANDLER);
and
sf::RenderWindow(sf::VideoMode(...),...);
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Dec 6, 2014
I can't get my 'Front End' view model's constructor to be called. If i remove my dependency from the mvvm-light framework and use MSDN mvvm paterns then the constructor is called. What am i doing wrong. It seem like there is a data context binding issue between my XMAL and my view model backing.
ViewModelLocator.cs
using GalaSoft.MvvmLight.Ioc;
using Microsoft.Practices.ServiceLocation;
using Point_Of_Sale.Model;
using System.Collections.Generic;
namespace Point_Of_Sale.ViewModel {
public class ViewModelLocator
[Code] ......
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Dec 29, 2014
#include <vector>
#include <iostream>
#include <iterator>
[Code]....
I am confused for first call to push_back copy constructor is called for second call I am expecting it to move class instance to new memory location there by trigering move and then inserting second class instance expected call:
Copy constructor
Move constructor
Copy constructor
but its calling
Copy constructor
Copy constructor
Move constructor
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Feb 15, 2014
This exercise is from C++ primer 5th edition. I have not understood everything about constructors, mainly about how they function.
Work prior to the exercise was creating a class called screen with some specifications. This is the class:
Code:
class screen{
public:
using pos = string::size_type;
screen() = default;
private:
pos height = 0;
pos width = 0;
pos cursor = 0;
string contents;
};
The exercise goes as follows:
Exercise 7.24: Give your Screen class three constructors: a defaultconstructor; a constructor that takes values for height and width and initializes the contents to hold the given number of blanks; and a constructor that takes values for height, width, and a character to use as the contents of the screen.
Giving the screen a default constructor was easy. The next part is probably easy aswell, I just dont understand what they mean when they say "and initalize the contents to hold the given number of blanks" and something in the 3rd part when they say "character to use as the contents of the screen".
Think I have made a breakthrough... Would the constructor for the second part look like this:
screen(pos ht, pos wd) : contents(ht*wd) {}
or something?
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Nov 12, 2013
In the below program, how can copy the array n[] into Array[]. The below is not working..
#include <iostream>
using namespace std;
class arrayPlay {
[Code] .....
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Dec 11, 2013
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?
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Nov 21, 2014
Class Car{
Private:
string* _ID;
bool _isFaulty;
int _location;
int _timer;
int _order;
vector<Road*> _roadPlan;
}
I want to implements Copy constructor (deep copy) and destructor, and I don't know how to treat the vector of pointers (Road is an object too)
Mor
Another thing, maybe I'll prefer using List instead of Vector, so i would like to see an implements of Copy constructor and destuctor with List too,
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Nov 24, 2014
I want to copy over values from x to y, and its not possible as i cant use "y" as a index in my pointer array.
Code:
CellularPhoneStock::CellularPhoneStock(CellularPhoneStock &origObj){
this->phonez[nrOfPhones]->setColour = origObj.getColour();
/*this->model = origObj.model;
this->nrOfType = origObj.nrOfType;
this->price = origObj.price;*/
nrOfPhones++;
}
My questions is, how can I use origObj and phonez combined to use the function getColour() ?
Btw, phones = CellularPhone * phonez[30];
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Nov 15, 2012
This is my class there is a problem with my copy constructor .. is that correct ??
struct Node {
Type info;
Node<Type> *next;
};
template <class Type>
class Queue
[Code] ....
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Jun 19, 2014
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.
#include <iostream>
#include <cstdlib>
#include <fstream>
#include <iomanip>
using namespace std;
typedef int eletype;
int const CAPACITY = 20;
[Code] ....
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Feb 3, 2014
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 :
ListType.h
#ifndef LISTTYPE_H
#define LISTTYPE_H
#include<iostream>
class ListType{
public:
ListType(size_t=10);
ListType(const ListType&);
[Code] ......
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May 20, 2013
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?
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Apr 6, 2014
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)
- There must exist a Linked list 'ShapeList':
ShapeList()
ShapeList( const ShapeList &shapes)
~ShapeList()
add( const Shape& s )
remove( const Vertex &v)
area()
print()
This is what I've created so far (Shape, ShapeList, Vertex):
main.cpp:
#include <iostream>
using namespace std;
#include "shapelist.h"
#include "vertex.h"
#include "shape.cpp"
[Code] ....
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Mar 13, 2013
I'm trying to do deep copy for my constructor
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.
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Oct 7, 2014
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
[code].....
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Nov 5, 2014
here is the list.h file
#include <iostream>
#include <iomanip>
#include <string>
using namespace std;
class Node {
[code]....
Ignore the optional part as i am not working with that at the moment. The problem is my program keeps crashing when deallocating. Not sure why.
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Nov 5, 2014
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.
Here is my header file:
#ifndef CANDIDATELIST_H
#define CANDIDATELIST_H
#include "CandidateType.h"
#include <iostream>
[Code].....
I know I don't have much in these functions but I'm not sure how to apply them or if I'm even headed in the right direction.
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Oct 28, 2014
Here is my code. It runs but after display result, it announce error
template <class T>
class LINKED_LIST {
private:
struct ListNode {
T data;
ListNode *next; // pointer to next node
[Code] ....
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Dec 10, 2012
Code:
class Matrix4 {
Matrix4(float mat[4][4]) {
memcpy (m, mat, 16);
}
float m[4][4];
};
float m[4][4];
cam->getProj(m);
Matrix4 matProj(m);
The above snippet doesn't compile, correcting mistakes in syntax.
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Sep 13, 2013
Go to this link : [URL] .....
Actually I am not getting one thing in this code that why they only provide the declaration of Copy constructor and Assignment operator...??
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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;
[Code] .....
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