Question

class A {};
class B { public: B (A a) {} };

A a;
B b=a;

I read this from http://www.cplusplus.com/doc/tutorial/typecasting/ . It says this is a implicit type conversion. From class A to class B.
I want to ask, is this also an example of copy constructor?
Thanks.

Answer 1

No, it’s not a copy constructor. A copy constructor copies one object of one type into another of the same type:

B::B(const B& b)
{
    // ...
}

As a side note, if you need a copy constructor then you also need a destructor and an assignment operator, and probably a swap function.

What B::B(A) is is a conversion function. It’s a constructor that allows you to convert an object of type A into an object of type B.

void f(const B& obj);

void g()
{
    A obja;
    B objb = obja;
    f(obja);
}