Passing a member function of a class as pointer

Question

Well this might be not the best solution to my problem so I will explain what I want to do.

I want to create a function which is a generic version of other classes (an interface in java way of seeing it). And then create a specialization of each class.

Later I want to create a vector of the generic class but each member of the vector is in reallity a casted member of the each specialized class. So when I call a function of each class in the vector call a diffrent function.

I tryied to do this using only inherence but, when I call the function of the vector call the implementation of the father and not it specialization.

I don't wnat to cast each member of the vector to call the right function because the hole point of doing this is to generalize a problem in the code. I mean make a dynamic behavor.

I also tryied to use pointers so the specialized class assign it function to a function pointer which is the one will be call. But this was not allowed because the pointer is namespace::classgeneralization::(int)(*f)(); and the function I want to point is namespace::classgeneralization::classspecialization::int f()(); so it do not compile.

I could may implemente the function out of the class and then point it in the class, but this is really ofuscate code I think. I also tryed to see if I could use a pointer to a lamda function but this is not posible at least in VS2010 as far I could research.

Maybe the hole perspective of solving the problem is wrong, and there is a way to do this properly and less ofuscate as I am trying. In any case I am open to other perspectives, so long I achive a vector of classes which each element is a different class with thiferent implementations of functions.

Reading your description, I think you should read about [object slicing](http://stackoverflow.com/questions/274626/what-is-the-slicing-problem-in-c). — Some programmer dude, May 27 '13 at 08:37
Also, reading about [`std::function`](http://en.cppreference.com/w/cpp/utility/functional/function) might be useful. Though I'm not sure it's fully supported in VS2010. — Some programmer dude, May 27 '13 at 08:38
I will like to know why the question was downgraded. If is because my poor english I am sorry but I find it unfair for not natives english speakers — user223506, May 27 '13 at 08:47
@user223506 Then your test is wrong or your copy of VS2010 is incomplete. — Captain Obvlious, May 27 '13 at 08:51
my test was wrong. Sorry about it. Thanks to @JoachimPileborg and Captain Obvlious. I think this will solve the problem — user223506, May 27 '13 at 08:57
@user223506 Now that your `std::function` test is working take a look at `std::bind`. It will come in handy as well. — Captain Obvlious, May 27 '13 at 09:01

tarjeik · Accepted Answer · 2013-05-27T11:29:14.290

1

It's a bit difficult to understand your question, but it sounds to me that you are trying to achieve polymorphism in a very cumbersome way. Maybe the following code helps:

#include <iostream>
#include <vector>

class MyInterface
{
public:
   virtual void f() { std::cout << "MyInterface::f() called" << std::endl; }
};

class A : public MyInterface 
{
public:
   virtual void f() { std::cout << "A::f() called" << std::endl; }
};

class B : public MyInterface 
{
};

int main()
{
   std::vector<MyInterface*> objects;
   objects.push_back(new A);
   objects.push_back(new B);

   objects[0]->f();
   objects[1]->f();

   return 0;
}

This will output:

A::f() called
MyInterface::f() called

edited May 27 '13 at 11:29

answered May 27 '13 at 09:02

tarjeik

94
6

I was trying to do somthing like this, but without creating pointers. Is posible to do this behavor without pointers, declare the objects and not as pointers to objects? – user223506 May 27 '13 at 09:57
No, as Joachim Pileborg mentioned in a comment to your question, using std::vector will result in slicing. See Joachims link for more information. I would also advise you to gain some more insight of values, references and pointers in C++. – tarjeik May 27 '13 at 11:22

Passing a member function of a class as pointer

1 Answers1