CODEWITHSUNDEEP
c++
H'H
H'H

Reputation: 1678

cannot access private member declared in class for make_unique

I have following classes: Class A with deleted copy constructor. 

class A
  {
  public:
    explicit A(int i_a) {a = i_a;};
    ~A(){};
  private:
    A(const A&) = delete;
    A& operator=(const A&) = delete;
    int a;
  };

and Class B with a unique_ptr member.

class A;
class B
  {
  public:
    B(int i_b);
    ~B() {};

  private:
    std::unique_ptr<A> p_b;
  };

and B.cpp:

B::B(int i_b)
  {
  p_b = std::make_unique<A>(A(i_b));
  }

I am receiving this error while making unique_ptr of class A:

'A::A': cannot access private member declared in class 'A'

Can someone please explain me why I am receiving this error? I know that by commenting this line "A(const A&) = delete;" error will be resolved. But I am looking for some explanation.

Upvotes: 1

Views: 1470

Answers (1)

Yksisarvinen
Yksisarvinen

Reputation: 22219

  p_b = std::make_unique<A>(A(i_b));

In this line you are trying to call copy constructor, which you have deleted (or move constructor, which is not declared)

Instead, you should use:

  p_b = std::make_unique<A>(i_b);

Or you could declare move constructors for your class:

class A
  {
  public:
    explicit A(int i_a) {a = i_a;};
    A(A&&) = default;
    A& operator=(A&&) = default;
    ~A(){};
  private:
    A(const A&) = delete;
    A& operator=(const A&) = delete;
    int a;
  };

std::make_unique will call a constructor of a given class, passing any arguments it has received as they are. So, if you pass an object of type A, it will try to use constructor which takes an argument of type A - i.e. copy constructor or move constructor.
Because you have declared copy constructor, move constructor was not automatically generated, so it couldn't have been used by std::make_unique

Upvotes: 7

Related Questions