copy constructor

Manj N

11y1.7k

what is copy constructor?

when, why we use copy constructor??

6 Replies

Know the answer? Post it — somebody with the same question will find it here.

Ken H11y ago
Copy Constructor by the following two parts:

1)Shallow Copy Constructor;
2)Deep Copy Constructor.
Shallow Copy Constructor is not the best approach,Because it will cause the application to crash.
Examples 1:

// Shallow Copy Constructor Demo.
class MyClass{
public:
MyClass(){
value = new int;
*value = 123;
}
MyClass(const MyClass &obj){
cout << "Shallow Copy Constructor completed..." << endl;
value = obj.value; // Shallow copy field.
}
~MyClass(){
delete value;
value = NULL;
}
void print() const{
cout << *value << endl;
}
void set(int i){
*value = i;
}
private:
int *value;
};
int main(void){
MyClass *mcObj= new MyClass();
cout << "mcObj.value=";
mcObj->print();
// Will call Shallow Copy Constructor.
MyClass mcObj2 = (*mcObj);
cout << endl << "mcObj2.value=";
mcObj2.print();
mcObj->set(456);
cout << endl << "Change after:";
mcObj2.print();
// Free the memory of mcObj.
delete mcObj;
// Trying to access the value of the field again.
// However, that may cause the application to crash.
mcObj2.print();
system("pause");
return 1;
}

Examples 2:
// Deep Copy Constructor Demo.
class MyClass{
public:
MyClass(){
value = new int;
*value = 123;
}
MyClass(const MyClass &obj){
cout << "Deep Copy Constructor completed..." << endl;
value = new int;
*value = *(obj.value); // Deep copy field.
}
~MyClass(){
delete value;
value = NULL;
}
void print() const{
cout << *value << endl;
}
void set(int i){
*value = i;
}
private:
int *value;
};
int main(void){
MyClass *mcObj= new MyClass();
cout << "mcObj.value=";
mcObj->print();
// Will call Deep Copy Constructor.
MyClass mcObj2 = (*mcObj);
cout << endl << "mcObj2.value=";
mcObj2.print();
mcObj->set(456);
cout << endl << "Change after:";
mcObj2.print();
// Free the memory of mcObj.
delete mcObj;
// Trying to access the value of the field again.
// Good,It is the results we expect, Print result is 123
mcObj2.print();
system("pause");
return 1;

}
Rakesh11y ago
Hello,

A Copy Constructor is a constructor that creates a new object by making a copy of an existing object.
Example

using System;
using System.Text;

namespace OPPS
{
class Constructor
{
class CopyConstructor
{
int a, b;
public CopyConstructor(int i, int j)
{
a=i;
b=j;
}
public CopyConstructor( CopyConstructor c)
{
a = c.a;
b = c.b;
}
public void OutPut()
{
Console.WriteLine("Value of A = {0}",a);
Console.WriteLine("Value of B = {0}", b);
}
}
static void Main(string[] args)
{
CopyConstructor CC = new CopyConstructor(5,3);
CopyConstructor copy = new CopyConstructor(CC);
CC.OutPut();
Console.WriteLine("------- VALUE COPY ----------");
copy.OutPut();
Console.ReadLine();
}
}
}

http://www.c-sharpcorner.com/UploadFile/b926a6/introduction-to-oops-in-C-Sharp/
Sujeet Suman11y ago
Copy Constructor: A constructor takes same class type as parameter is call copy constructor. It is used to instrantiate new intance with the same values of existing.

class Test
{
   // Copy constructor.
   public Test(Test previousTest)
   {
      Name = previousTest.Name;
      Age = previousTest.Age;
    }
}
Gowtham K11y ago
Try this,
http://www.onlinebuff.com/article_explain-the-copy-and-private-constructor-with-an-example-in-c_13.html
http://www.aspdotnet-suresh.com/2013/09/csharp-copy-constructor-with-example.html
Manj N11y ago
i have one doubt in copy constructor

class name
{
int a;
public:
name(int x)
{a=x;
}
name(name &ob)
{
}
};
void main()
{
name n1(2);
name n2=n1;
}

when object is created memory is allocated for that object. Right?
here 2 objects are created(n1 and n2). memory location of both n1 and n2 are same or different?
Rajeesh Menoth11y ago
Hi,

Ref the following links..
1) http://www.cplusplus.com/articles/y8hv0pDG/

2) http://www.tutorialspoint.com/cplusplus/cpp_copy_constructor.htm

3) http://www.codeproject.com/Questions/205205/Why-we-need-the-Copy-Constructor-the-Assignment-Op