Question

I just asked this question and the good answers mentioned using an initialization list. So I looked it up in many various places. It was often said that one can use an initialization list to select which constructor to use.

class First
   {private: 
         int a, b, c;
  public:
First(int x);
First(int x, int y);
}

First::First(int x, int y, int z = 0)
{ /* this is a constructor that will take two or three int arguements. */ }

First::First(int x, int y = 0, int z = 0)
{ /* and this will be called if one arguement is given */ }

I thought all assignments should be avoided, so how would I write the initializer lists for these two constructors?

Answer 1

I’m not quite sure I follow. As it stands, by providing an argument to x and y (and therefore z), both constructors will be available to call, resulting in ambiguity.

I think what you’re looking for is:

class First
{
public:
  First(int x);
  First(int x, int y, int z = 0);
};    

// invoked as First f(1);
First::First(int x) :
a(x), b(0), c(0)
{}

// invoked as First f(1, 2); or First f(1, 2, 3);
First::First(int x, int y, int z) :
a(x), b(y), c(z)
{}