Programming Forums > Application Development > C++

l2u · Aug 14th, 2007, 10:00 PM

Hello

I would like to do:

Code:

std::list<some_templated_class> _list;
_list.push_back(some_templated_class<some_object>(arguments));

but my compiler wont allow me to compile this. I get error:
unspecialized class template can't be used as a template argument for template parameter '_Ty', expected a real type

Is there any other way to be able to do/override this?

Thanks for help

Jessehk · Aug 14th, 2007, 10:47 PM

I'm pretty sure you have to specify the template specialization of the class your list is holding when you declare it.

For example, instead of

(Toggle Plain Text)

std::list<Foo> _list;

You should write:

(Toggle Plain Text)

std::list<Foo<int> > _list;

That would be my guess anyway.

l2u · Aug 14th, 2007, 11:06 PM

Yeah but what if I dont know I want different types, not just int?
Maybe boost::any, boost::variant of anyone knows of better approach?

Game_Ender · Aug 15th, 2007, 12:34 AM

The you should use a common base class like so:

 cpp Syntax (Toggle Plain Text) 
#include <vector>
 
class Base
{
};
 
template<class T>
class Templated : public Base
{
public:
    Templated(T val) : _val(val) {};
    T _val;
};
 
int main()
{
    // Note this works if you remove the pointers and the "new" statements
    // but I am not sure if you actually get at the derived object anymore
    std::vector<Base*> list;
    list.push_back(new Templated<int>(1));
    list.push_back(new Templated<double>(2.3));
 
    return 0;
}
#include <vector>

class Base
{
};

template<class T>
class Templated : public Base
{
public:
    Templated(T val) : _val(val) {};
    T _val;
};

int main()
{
    // Note this works if you remove the pointers and the "new" statements
    // but I am not sure if you actually get at the derived object anymore
    std::vector<Base*> list;
    list.push_back(new Templated<int>(1));
    list.push_back(new Templated<double>(2.3));
    
    return 0;
}

grumpy · Aug 15th, 2007, 7:42 AM

The answer to the original questions is that _list needs to be declared as;

(Toggle Plain Text)

std::list<some_templated_class<some_object> > _list;

If _list is a member of a templated class, it is necessary to insert the typename keyword; I'll leave working out where as an exercise.

Incidentally, it is not generally a good idea to have leading or trailing underscores on identifier names.

l2u · Aug 16th, 2007, 8:57 PM

Actually I would like to store handlers in containers (boost.bind), but I thought it would be the best to store them in new templated object.

I'd like to be able to do:

(Toggle Plain Text)

container.pushback(boost::bind(&Test::func,&test, someargument, argument2));

Game_Ender · Aug 17th, 2007, 2:27 AM

You use boost.function of course.

Aug 14th, 2007, 10:00 PM	#1
l2u Newbie Join Date: Mar 2007 Posts: 24 Rep Power: 0	template specialization problem Hello I would like to do: Code: (Toggle Plain Text) std::list<some_templated_class> _list; _list.push_back(some_templated_class<some_object>(arguments)); std::list<some_templated_class> _list; _list.push_back(some_templated_class<some_object>(arguments)); but my compiler wont allow me to compile this. I get error: unspecialized class template can't be used as a template argument for template parameter '_Ty', expected a real type Is there any other way to be able to do/override this? Thanks for help

Aug 14th, 2007, 10:47 PM	#2
Jessehk The Oblivious One Join Date: May 2005 Location: Ontario, Canada Posts: 648 Rep Power: 4	I'm pretty sure you have to specify the template specialization of the class your list is holding when you declare it. For example, instead of (Toggle Plain Text) std::list<Foo> _list; std::list<Foo> _list; You should write: (Toggle Plain Text) std::list<Foo<int> > _list; std::list<Foo<int> > _list; That would be my guess anyway. __________________ Dr. Zoidberg: [ecstatic] I'm going to a movie... with FRIENDS!

Aug 15th, 2007, 12:34 AM	#4
Game_Ender Professional Programmer Join Date: May 2006 Location: Maryland, USA Posts: 306 Rep Power: 3	The you should use a common base class like so: cpp Syntax (Toggle Plain Text) #include <vector> class Base { }; template<class T> class Templated : public Base { public: Templated(T val) : _val(val) {}; T _val; }; int main() { // Note this works if you remove the pointers and the "new" statements // but I am not sure if you actually get at the derived object anymore std::vector<Base> list; list.push_back(new Templated<int>(1)); list.push_back(new Templated<double>(2.3)); return 0; } #include <vector> class Base { }; template<class T> class Templated : public Base { public: Templated(T val) : _val(val) {}; T _val; }; int main() { // Note this works if you remove the pointers and the "new" statements // but I am not sure if you actually get at the derived object anymore std::vector<Base> list; list.push_back(new Templated<int>(1)); list.push_back(new Templated<double>(2.3)); return 0; } __________________ Robotics @ Maryland AUV Team - Software Lead

Aug 15th, 2007, 7:42 AM	#5
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,260 Rep Power: 5	The answer to the original questions is that _list needs to be declared as; (Toggle Plain Text) std::list<some_templated_class<some_object> > _list; std::list<some_templated_class<some_object> > _list; If _list is a member of a templated class, it is necessary to insert the typename keyword; I'll leave working out where as an exercise. Incidentally, it is not generally a good idea to have leading or trailing underscores on identifier names.

Aug 16th, 2007, 8:57 PM	#6
l2u Newbie Join Date: Mar 2007 Posts: 24 Rep Power: 0	Actually I would like to store handlers in containers (boost.bind), but I thought it would be the best to store them in new templated object. I'd like to be able to do: (Toggle Plain Text) container.pushback(boost::bind(&Test::func,&test, someargument, argument2)); container.pushback(boost::bind(&Test::func,&test, someargument, argument2));

Aug 14th, 2007, 11:06 PM	#3
l2u Newbie Join Date: Mar 2007 Posts: 24 Rep Power: 0	Yeah but what if I dont know I want different types, not just int? Maybe boost::any, boost::variant of anyone knows of better approach?

Aug 17th, 2007, 2:27 AM	#7
Game_Ender Professional Programmer Join Date: May 2006 Location: Maryland, USA Posts: 306 Rep Power: 3	You use boost.function of course. __________________ Robotics @ Maryland AUV Team - Software Lead

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Programming Forums > Application Development > C++

template specialization problem