Constructor that take parameters as default

Question

My code is

template <class T1, class T2>
class MyClass
{

    T1 first;
    T2 second;
    public:
    //default constructor
    MyClass():first(T1()), second(T2()) {}
}

I want to have a single constructor which can take 0, 1 or 2 arguments (parameters as default). Here T1 and T2 can be both primitive as well as non-primitive types.

Answer 1

Replace your existing constructor with this constructor:

MyClass(const T1& t1 = T1(), const T2& t2 = T2()):first(t1), second(t2) {}

Answer 2

Try this:

template <class T1, class T2>
class MyClass
{

    T1 first;
    T2 second;
    public:
    //default constructor
    MyClass(T1 fst=T1(), T2 sec = T2()):first(fst), second(sec) {}
};

int main()
{
    MyClass<int,int> c;
    MyClass<int,int> d(5);
    MyClass<int,int> e(5,10);
}

You have to just assign the default value in the definition. You have to be careful that default arguments are always the last in the list of arguments. And that one constructor is all that's needed in all the situations of 0, 1 or 2 arguments.

Answer 3

Default parameters can be use in constructor initializer list as for all other functions.

 MyClass(T1 t1 = T1(), T2 t2 = T2()) : first(t1), second(t2) {}