构造函数作为默认参数

Question

let's say i have 2 classes

class B
{
   B() { /* BLA BLA */ };
   B(int a) { /* BLA BLA */ };
   B(int a,int b) { /* BLA BLA */ };
}

class A {
public :
  A(B  par);
}

i was wondering how can i call A's constructor with par having a deafult argument, as each of B constructors. (of course i would like see 3 examples, i don't expect all of them to exist together)

thanks

Answer 1

You can do something like:

A(B par = B())
A(B par = B(1))
A(B par = B(1,2))

Full code as per comment:

class B
{
public:
   B() {  };
   B(int a) {};
   B(int a,int b) {};
};

class A {
public :
  A(B  par = B()/* or B(1) or B(1,2) */);

};

Answer 2

A(B());//create a B object and pass it to A
A(B(1));
A(B(1,2));

or define 3 different constructor for A(but that does not sound good to me).