Inheriting from a template class in c

Question

Let s say we have a template class Area  which has a member variable T area  a T getArea   and a void setArea T  member functions   I can create an Area object of a specific type by typing Area lt int gt    Now I have a class Rectangle that inherits the Area class  Since Rectangle itself is not a template  I cannot type Rectangle lt int gt    How do I specialize the inherited Area type for Rectangle objects   EDIT  Sorry  I forgot to clarify - my questions is whether it is possible to inherit Area without specializing it  so it is not inherited as Area of ints but as Area Rectangle can specialize the types for

User · Answer

class Rectangle   public Area lt int gt

User · Answer

Are you just trying to derive from Area lt int gt   In which case you do this   class Rectangle   public Area lt int gt                    EDIT  Following the clarification  it seems you re actually trying to make Rectangle a template as well  in which case the following should work   template  lt typename T gt  class Rectangle   public Area lt T gt

User · Answer

include lt iostream gt   using namespace std   template lt class t gt   class base   protected      t a  public      base t aa           a   aa          cout lt  lt  base   lt  lt a lt  lt endl            template  lt class t gt   class derived  public base lt t gt       public          derived t a   base lt t gt  a                        Here is the method in derived class      void sampleMethod             cout lt  lt  In sample Method  lt  lt endl            int main         derived lt int gt  q 1          calling the methods     q sampleMethod

User · Answer

Make Rectangle a template and pass the typename on to Area   template  lt typename T gt  class Rectangle   public Area lt T gt

User · Answer

Rectangle will have to be a template  otherwise it is just one type  It cannot be a non-template whilst its base magically is   Its base may be a template instantiation  though you seem to want to maintain the base s functionality as a template

User · Answer

For understanding templates  it s of huge advantage to get the terminology straight because the way you speak about them determines the way to think about them   Specifically  Area is not a template class  but a class template  That is  it is a template from which classes can be generated  Area lt int gt  is such a class  it s not an object  but of course you can create an object from that class in the same ways you can create objects from any other class   Another such class would be Area lt char gt   Note that those are completely different classes  which have nothing in common except for the fact that they were generated from the same class template   Since Area is not a class  you cannot derive the class Rectangle from it  You only can derive a class from another class  or several of them   Since Area lt int gt  is a class  you could  for example  derive Rectangle from it   class Rectangle    public Area lt int gt                  Since Area lt int gt  and Area lt char gt  are different classes  you can even derive from both at the same time  however when accessing members of them  you ll have to deal with ambiguities    class Rectangle    public Area lt int gt     public Area lt char gt                  However you have to specify which classed to derive from when you define Rectangle  This is true no matter whether those classes are generated from a template or not  Two objects of the same class simply cannot have different inheritance hierarchies   What you can do is to make Rectangle a template as well  If you write  template lt typename T gt  class Rectangle    public Area lt T gt                  You have a template Rectangle from which you can get a class Rectangle lt int gt  which derives from Area lt int gt   and a different class Rectangle lt char gt  which derives from Area lt char gt    It may be that you want to have a single type Rectangle so that you can pass all sorts of Rectangle to the same function  which itself doesn t need to know the Area type   Since the Rectangle lt T gt  classes generated by instantiating the template Rectangle are formally independent of each other  it doesn t work that way  However you can make use of multiple inheritance here   class Rectangle    not inheriting from any Area type        Area independent interface     template lt typename T gt  class SpecificRectangle    public Rectangle    public Area lt T gt         Area dependent stuff     void foo Rectangle amp       A function which works with generic rectangles  int main       SpecificRectangle lt int gt  intrect    foo intrect      SpecificRectangle lt char gt  charrect    foo charrect       If it is important that your generic Rectangle is derived from a generic Area you can do the same trick with Area too   class Area        generic Area interface     class Rectangle    public virtual Area    virtual because of  diamond inheritance         generic rectangle interface     template lt typename T gt  class SpecificArea    public virtual Area        specific implementation of Area for type T     template lt typename T gt  class SpecificRectangle    public Rectangle     maybe this should be virtual as well  in case the hierarchy is extended later   public SpecificArea lt T gt     no virtual inheritance needed here        specific implementation of Rectangle for type T

[c++] Inheriting from a template class in c++

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