C++ object instantiations

Question

This question is about object instantiations in C++. There are several ways to instantiate objects both on heap and on stack I am curious to know the subtle differences.

using namespace std;

class Raisin
{
private:
    int x;
public:
    Raisin():x(3){}
    Raisin(int input):x(input){}
    void printValue()
    {
       cout<< "hey my Deliciousness is: " << x <<endl;
    }
};

Basically Raisin is a simple class that I am using for this demonstration:

int main()
{

Raisin * a= new Raisin;
a->printValue();

Raisin * b= new Raisin{};
b->printValue();

Raisin * c= new Raisin();
c->printValue();

Raisin x;
x.printValue();

Raisin y{};
y.printValue();

Raisin z();
z.printValue(); 
//error: request for member 'printValue' in 'z', 
//which is of non-class type 'Raisin()'


Raisin alpha(12);
alpha.printValue();

Raisin omega{12};
omega.printValue();

return 0;
}

I would like to know why Raisin * c can be instantiated with empty parenthesis, but but Raisin z cannot be. (Actually Raisin z() is legal but incorrect)

Also I understand there is a subtle difference between Raisin (2) and Raisin{2}. I would appreciate if someone can shed light on the idiosyncrasies.

Answer 1

This line

Raisin z();

Declares a function (with no argument) returning a Raisin object, not a default-constructed Raisin