Impossible constructor

Question

So I have this code :

class A{
public:
    A(){}
    A(int){}
};
int main(){
    A x;//I want this to give me error
    A x(1);//or this to give me error
return 0;
}

How to make the class to be impossible to be constructed? without changing visibility of the constructors;

Why do you want a type that cannot be instantiated at all? That hardly sounds useful. — Baum mit Augen, Jun 02 '16 at 11:34
But A x(1); still works , yes something that cannot be instatiated — Ciomegu, Jun 02 '16 at 11:36
I'm not a C++ expert and may miss something but why not throw an exception inside the constructor ? Isn't it what OP means by 'give me an error' ? — Diane M, Jun 02 '16 at 11:36
@Ciomegu you need to think outside the box and extrapolate the idea presented by Piotr to the other constructor as well. — eerorika, Jun 02 '16 at 11:37
Ok ok , but is there any other way? I understood this only works in c++ 11 but what about other versions — Ciomegu, Jun 02 '16 at 11:39
@Ciomegu if your question is about an older standard, please add its tag ([c++98], [c++03] or [c++11]) to the question. — Quentin, Jun 02 '16 at 12:01
@Ciomegu the way to do it in earlier standard versions was to declare the constructors private. — eerorika, Jun 02 '16 at 13:35

score 5 · Answer 1 · answered Jun 02 '16 at 11:34

5

You could remove the user-defined constructor, and make the default constructor deleted (since C++11).

class A{
public:
    A() = delete;
};

answered Jun 02 '16 at 11:34

songyuanyao

is there any other way? – Ciomegu Jun 02 '16 at 11:40
1

@Ciomegu The pre-C++11 way is make constructors private and don't define them. But you said don't want to change visibility... – songyuanyao Jun 02 '16 at 11:42
I actually found out, make something virtual then equal to 0;Thank you – Ciomegu Jun 02 '16 at 11:43
1

@Ciomegu: You're talking about pure virtual functions. This does not apply to class constructors. Pure virtual functions will actually force derived classes to implement the function after all. – AndyG Jun 02 '16 at 11:51

1 Answers1