When an object is created, compiler
automatically creates a copy constructor and overloaded
assignment (=) operator. We can also define copy constructor and overloaded
assignment (=) operator in our class. When we assign a object to another object
of same class, then either copy constructor or overloaded assignment operator
can be called, depending upon where we assigning object.
If we assigning a object to another
object at the time of declaration, then copy constructor is called, for
example,
class-name object1 = object2;
If we assigning a object to another
object after the declaration, then overloaded assignment operator is called,
for example,
class-name object1;
object1 = object2;
Shallow Copy
In shallow copy, an object
copies all data and all resources from another object of same class. For
example, if a class has two variables and one pointer, then if we assign
object1 to object2 of that class, then content of two variables and one pointer
is copied into object2. Now the problem is pointer of object2 is also pointing
same memory block pointed by pointer of object1, which is disastrous.
Example:
#include<iostream>
using namespace std;
class Example
{
private:
int var1, var2;
float *ptr;
public:
Example()
{
ptr = new
float;
}
Example(Example &o)
{
var1 =
o.var1;
var2 =
o.var2;
ptr =
o.ptr;
}
void setData(int a, int
b, float c)
{
var1 = a;
var2 = b;
*ptr = c;
}
void displayData()
{
cout<<endl<<var1;
cout<<endl<<var2;
cout<<endl<<*ptr;
}
} ;
int main()
{
Example obj1;
obj1.setData(1, 2, 3.5);
Example obj2 = obj1;
obj2.displayData();
return 0;
}
OUTPUT:
1
2
3.5
In this example, pointer of both obj1
and obj2 is pointing to same float variable.
Deep Copy
In deep copy, content of an object is
copied to other object of same class. But exact resources allocated to an
object is not copied to other object. In deep copy, another resources are
created and then assigning to other object.
Example:
#include<iostream>
using namespace std;
class Example
{
private:
int var1, var2;
float *ptr;
public:
Example()
{
ptr = new
float;
}
Example(Example &o)
{
var1 =
o.var1;
var2 =
o.var2;
ptr = new
float;
*ptr =
*(o.ptr);
}
void setData(int a, int
b, float c)
{
var1 = a;
var2 = b;
*ptr = c;
}
void displayData()
{
cout<<endl<<var1;
cout<<endl<<var2;
cout<<endl<<*ptr;
}
} ;
int main()
{
Example obj1;
obj1.setData(1, 2, 3.5);
Example obj2 = obj1;
obj2.displayData();
return 0;
}
OUTPUT:
1
2
3.5
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