Which is the difference between declaring a constructor private and =delete?

Question

For example, I want to declare a class but I want the client to not be able to use the copy constructor (or copy assignment operator)

Both of the following two does not allow the use of the copy constructor:

1.

class Track
{
public:
  Track(){};
  ~Track(){};
private:
  Track(const Track&){};
};

2.

class Track
{
public:
  Track(){};
  ~Track(){};
  Track(const Track&)=delete;
};

Is one of these ways "more correct" than the other or are equal? Is there any side-effect?

//Does not compile with both the above ways
int main()
{
  Track l;
  Track p(l);
}

Answer 1

Making it private is the "old" way of doing it. The constructor still exists, but it is private, and can only be invoked from within another class member function.

= delete deletes the constructor. It is not generated by the compiler, and it simply will not exist.

So most likely, = delete is what you want. (although with the caveat that not all compilers support this syntax yet, so if portability is a concern...)

Answer 2

Declaring a copy constructor private still allows member functions of the Track class to copy-construct instances of that class, while making it deleted simply forbids copy-constructing that object.

In C++11, deleting a copy constructor is the right way to express the fact that a class is non-copyable (unless of course it makes sense for you to let member functions of Track, or friends of Track, to copy-construct Track objects).