The copy constructor is a constructor which creates an
object by initializing it with an object of the same class, which has been
created previously. The copy constructor is used to:
- Initialize one object from another of the same type.
- Copy an object to pass it as an argument to a function.
- Copy an object to return it from a function.
If a copy
constructor is not defined in a class, the compiler itself defines one. If the
class has pointer variables and has some dynamic memory allocations, then it is
a must to have a copy constructor.
The syntax for user defined Copy constructor is
class_name(class_name
& obj)
{
//
body of constructor
}
program:
#include <iostream>
using namespace std;
class Line
{
public:
int getLength( void );
Line( int len ); // simple constructor
Line( const Line
&obj); // copy constructor
~Line(); // destructor
private:
int *ptr;
};
// Member functions definitions including constructor
Line::Line(int len)
{
cout <<
"Normal constructor allocating ptr" << endl;
// allocate memory for
the pointer;
ptr = new int;
*ptr = len;
}
Line::Line(const Line &obj)
{
cout << "Copy
constructor allocating ptr." << endl;
ptr = new int;
*ptr = *obj.ptr; // copy
the value
}
Line::~Line(void)
{
cout <<
"Freeing memory!" << endl;
delete ptr;
}
int Line::getLength( void )
{
return *ptr;
}
void display(Line obj)
{
cout <<
"Length of line : " << obj.getLength() <<endl;
}
// Main function for the program
int main( )
{
Line line(10);
display(line);
return 0;
}
After Execution Result
Normal constructor allocating ptr
Copy constructor allocating ptr.
Length of line : 10
Freeing memory!
Freeing memory!
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