❮ Cpp Conditional Operator Cpp Functions ❯

C++`Copy Constructor`

Copy Constructor is a special constructor that initializes a new object using an object of the same class that was created earlier. The copy constructor is typically used for:

Initializing a new object with another object of the same type.
Copying an object to pass it as an argument to a function.
Copying an object to return it from a function.

If a copy constructor is not defined in a class, the compiler supplies its own copy constructor. If the class has pointer variables and has dynamic memory allocation, it must have a copy constructor. The most common form of the copy constructor is as follows:

classname (const classname &obj) {
   // Constructor body
}

Here, obj is a reference to an object that is used to initialize another object.

Example

#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 function definitions, including constructor
Line::Line(int len)
{
    cout << "Calling constructor" << endl;
    // Allocate memory for the pointer
    ptr = new int;
    *ptr = len;
}

Line::Line(const Line &obj)
{
    cout << "Calling copy constructor and allocating memory for pointer 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 << "line size : " << obj.getLength() <&lt;endl;
}

// Main function of the program
int main( )
{
   Line line(10);

   display(line);

   return 0;
}

When the above code is compiled and executed, it produces the following result:

Calling constructor
Calling copy constructor and allocating memory for pointer ptr
line size : 10
Freeing memory
Freeing memory

The following example modifies the above example slightly by initializing a new object using an existing object of the same type:

Example

#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 function definitions, including constructor
Line::Line(int len)
{
    cout << "Calling constructor" << endl;
    // Allocate memory for the pointer
    ptr = new int;
    *ptr = len;
}

Line::Line(const Line &obj)
{
    cout << "Calling copy constructor and allocating memory for pointer 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 << "line size : " << obj.getLength() <&lt;endl;
}

// Main function of the program
int main( )
{
   Line line1(10);

   Line line2 = line1; // This also calls the copy constructor

   display(line1);
   display(line2);

   return 0;
}

return 0;
}

When the above code is compiled and executed, it produces the following result:

Calling constructor
Calling copy constructor and allocating memory for pointer ptr
Calling copy constructor and allocating memory for pointer ptr
line size: 10
Freeing memory
Calling copy constructor and allocating memory for pointer ptr
line size: 10
Freeing memory
Freeing memory
Freeing memory

C++ Classes and Objects

❮ Cpp Conditional Operator Cpp Functions ❯

C++Copy Constructor

Example

Example

C++`Copy Constructor`