C ++子类将字段的父类命名错误

Question

I'm trying to modify a C++ project for my own use and am having trouble creating a derived class.

When I have the constructor for the derived class call its parent's constructor, I get an error message saying that the derived class does not have a field corresponding to the name of its parent's class . I don't understand where my problem lies.

The relevant parts of the .h file are as follows:

// grandparent_class ////////////////////////////////////////////////////////////////

template <typename T, typename Tds1 = T, typename Tds2 = T>
class grandparent_class : public module_1_1<T> {
 public:
  grandparent_class(uint nfeatures, const char *name = "grandparent_class");
  virtual ~grandparent_class();

// parent_class ////////////////////////////////////////////////////////////////

template <typename T, typename Tds1 = T, typename Tds2 = T>
class parent_class : public grandparent_class<T,Tds1,Tds2> {
 public:

  parent_class(uint nclasses, double target_factor = 1.0,
       bool binary_target = false,
       t_confidence conf = confidence_max,
       bool apply_tanh = false, const char *name = "parent_class",
       int force_class = -1, int single_output = -1,
       idxdim *kerd = NULL, double sigma_scale = 3,
                         bool silent = false);
  virtual ~parent_class();

  // members
  protected:
    int ctr;
};

// child_class (The Class I'm Introducing)////////////////////////////////////////////
template <typename T, typename Tds1 = T, typename Tds2 = T>
class child_class : protected parent_class<T,Tds1,Tds2> {
 public:
  child_class(uint nclasses, double target_factor = 1.0,
           bool binary_target = false,
           t_confidence conf = confidence_max,
           bool apply_tanh = false, const char *name = "child_class",
           int force_class = -1, int single_output = -1,
           idxdim *kerd = NULL, double sigma_scale = 3,
           bool silent = false);

virtual ~child_class();
};
//////////////////////////////////////////////////////////////////////////////

I define the constructor for my child class as follows:

//////////////////////////////////////////////////////////////////////////////

template <typename T, typename Tds1, typename Tds2>
child_class<T,Tds1,Tds2>::
child_class(uint nclasses, double target_factor, bool binary_target_,
            t_confidence conf, bool apply_tanh_, const char *name_,
            int force, int single, idxdim *kerd, double sigma_scale,
                     bool silent)
    : parent_class(nclasses, target_factor, binary_target_,
         conf, apply_tanh_, name_,
         force, single, kerd, sigma_scale, silent)
  {
    ...
  };

My child class declaration and definition are in the same file as the parent & grandparent declaration and definition, so I don't think there's an issue of a missing "include". As nearly as I can tell, my syntax for indicating inheritance is correct and I am calling the parent class's constructor correctly.

Yet, when I compile, I get the following error:

/home/me/ebl_answer.hpp: In constructor ‘ebl::child_class<T, Tds1, Tds2>::child_class(uint, double, bool, ebl::t_confidence, bool, const char*, int, int, ebl::idxdim*, double, bool)’:
/home/me/ebl_answer.hpp:416:4: error: class ‘ebl::child_class<T, Tds1, Tds2>’ does not have any field named ‘parent_class’
  : parent_class(nclasses, target_factor, binary_target_,

If anyone can see my mistake it would be very helpful....

Answer 1

In order to use inheritance, the class inherited from must be fully defined. You can't inherit from a class template, as it is not a type, it is just something that will be used to stamp out (instantiate) a real type. This is what you are doing in the declaration. Same goes for invoking the constructor of the base class.

Try using parent_class<T, Tds1, Tds2>

template <typename T, typename Tds1, typename Tds2>
child_class<T,Tds1,Tds2>::
child_class(uint nclasses, double target_factor, bool binary_target_,
            t_confidence conf, bool apply_tanh_, const char *name_,
            int force, int single, idxdim *kerd, double sigma_scale,
                     bool silent)
    : parent_class<T, Tds1, Tds2>(nclasses, target_factor, binary_target_,
         conf, apply_tanh_, name_,
         force, single, kerd, sigma_scale, silent)
  {
      ...
  }

See this live example .

Answer 2

As far as I can tell, you are simply missing a }; at the end of grandparent class. When I added that (and tweaked the code to remove classes I don't have), it compiled fine in VS.