如何声明默认构造函数

Question

I have a Base class that I can't modify the source code. I make a derived class from it and I am trying to make a no-argument constructor for this derived class. The problem is that I can't define the constructor for two reasons: There is not a non-argument constructor defined for the base class to use it. I can't pass a default value for the constructor of the base.

  class base
  {
      public:
      base (A arg)
      {

      }
  };

  class derived : public base
  {
      public:
      derived () : base (arg)  //ERROR
      {

      }
  };

Is there a solution to define a non-argument constructor for the derived class? Cordialement,

Answer 1

Since you cannot change the base class the only option left is to pass an argument to its constructor. You can do this quite easily by constructing a temporary instance of A and passing it to the base class in your ctor initialized list of derived classes.

derived::derived () : base (A())
{
}

In the code above base(A()) will create a temporary instance of A and pass it to the constructor of base .