C++ class copy constructor has no matching function - c++

Question

I am trying to write a class Core, it's member variable is a pointer. The copy constructor is Core(Core& x) instead of Core(const Core& x).
Core has a member function Core Core::new_core (int * ptr), the code has a problem when I try to construct Core new_core= core.new_core(ptr);, please see the code and error information below.
#include<iostream>
class Core
{
private:
int* a;
public:
Core(int* in) {a=in;}
Core(Core& x) {a = x.data();}
inline const int * data() const {return a;}
inline int * data() {return a;}
Core new_core (int * ptr)
{
Core b(ptr);
return b;
}
};
using namespace std;
int main()
{
int ptr[3]= {1,2,3};
Core core(ptr);
Core new_core= core.new_core(ptr);
cout<< new_core.data() <<endl;
return 0;
}
Error information:
main.cpp: In function ‘int main()’:
main.cpp:30:37: error: no matching function for call to ‘Core::Core(Core)’
Core new_core= core.new_core(ptr);
^
main.cpp:30:37: note: candidates are:
main.cpp:12:6: note: Core::Core(Core&)
Core(Core& x) { a = x.data() ;}
^
main.cpp:12:6: note: no known conversion for argument 1 from ‘Core’ to >‘Core&’
main.cpp:10:6: note: Core::Core(int*)
Core(int* in) {a=in;}
^
main.cpp:10:6: note: no known conversion for argument 1 from ‘Core’ to
‘int*’
I can easily fix the problem by replacing
Core(Core& x) { a = x.data() ;}
to
Core(const Core& x) { a = const_cast<int* > ( x.data() ) ;},
is there a better way to solve the problem without using const_cast?
I want to keep int* a private, and keep following two lines:
inline const int * data() const {return a;}
inline int * data() {return a;}
Thank you.

Answer 1

The problem here is that new_core returns a Core which is a temporary. When you use it in
Core new_core= core.new_core(ptr);
The compiler calls the copy constructor but it cannot bind to that temporary since it takes a reference. To fix this we can change the copy constructor to take a const Core& which can bind to the temporary and allow you to make a copy.
In this example to get around the const and the use ofconst_cast we can access the class member directly like:
Core(const Core& x) : a(x.a) {}