CODEWITHSUNDEEP
c++overloading
DisplayName
DisplayName

Reputation: 249

Overload of operators and constructor of copy

C++ requires create constructor of copies for assignment one instance to another instance. For example: 

my_class a = b;

It's wrong if I would implied copying, because it works as assignment of the address. Therefore, if I change a, b will be changed too. So, I should create constructor of copy:

my_class(const my_class &obj);

It seems as obvious thing and rest is going without saying, but I have gotten a doubt, when I found out about overload operators:

my_class operator=(my_class obj);

Turns out that I could use it as assignment and I don't have to use constructor of copies. Is that right? However, why assignment that is placed in the definition of operator= works as copying.

Upvotes: 0

Views: 61

Answers (1)

Serg
Serg

Reputation: 51

You can use or the copy assignment, as well as the constructor of copies.

class A {
  A(const A& a);
  A& operator=(const A& a);
};

A a1;
A a2(a1);  // calling constructor of copies A(const A& a);
A a2 = a1; // also calling constructor of copies A(const A& a);
A a3;
a3 = a1;   // calling copy assignment operator=(const A& a);

Here is example implementation:

class A
{
public:

  int* x;

  A(int data)
  {
    this->x = new int(data);
  }

  A(const A& a)
  {
    this->operator=(a);
  }

  A& operator=(const A& a)
  {
    this->x = new int(*a.x);
    return *this;
  }
};

Also you can provide special checks to avoid self-assignment, e.g. if (a != this)

Upvotes: 1

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