Default Constructor

Giriş
Kullanıcı herhangi bir constructor metodu yazarsa üretilmez. Açıklaması şöyle.

A default constructor is one without any parameters. Normally, it is provided for you. But if you explicitly define any other constructor, then it is not.

Açıklaması şöyle.

If no user-declared constructors of any kind are provided for a class type (struct, class, or union), the compiler will always declare a default constructor as an inline public member of its class.

const Alan
default constructor kullanmak için const alanlara değer atamak gerekir. Şu kod derlenmez.

class Bond
{
public:
  Bond(int payments_per_year, int period_lengths_in_months);
  Bond() = default;

private:
  const int payments_per_year;
  const int period_length_in_months;
};

int main()
{
  Bond b; // Error here
}

Şöyle yaparız.

const int payments_per_year = {12};

Defaulted Default Constructor

Örnek

Açıklaması şöyle. Yani sınıfın başka bir constructor'ı varsa ve derleyici halen default constructor üretsin istiyorsak kullanılır.

Dog() = default; is a user declared constructor (not to be confused with a user defined constructor). It is a defaulted default constructor. Typically you would use it when the class has other constructors but you still want the compiler to generate a default constructor (or rather a "defaulted default constructor". This is C++ terminology at its best. Note how the two "default"s have slightly different meaning).

Şöyle yaparız

class Dog
{
private:
    int x;
public:
    Dog()=default;
};