C++ call constructor from class pointer?

Question

I would like to be able to initialize a class from a string (I give "MyClass" and it would create an object MyClass).

I know it is not possible to do that so I created a class that has a map with a string as a key and a pointer to a function (that creates the object) as a value.

Creating dynamically the object is not a problem with this and my map.

template<typename T> JsonSerializable* createInstance() { return new T; }

My problem is that I want to add dynamically the classes to my map. Is that possible ? How can I do :

void MyFactory::addNewClass(std::string& name, class c)
{
    map[name]=&createInstance<c>();
}

Can I pass a pointer or something to the class itself (not the object) ? And use that to create dynamically everything.

If it is not possible I will have to hardcode it.

Answer 1

Ok.. So if you're using C++11 then lambdas can be of some help in getting the generic behaviour you're looking for.

First of all, we need a SuperBase from which all the classes shall be derived like this

class SuperBase {};
class A : public SuperBase {};

class B: public SuperBase {};

Then create a map which takes std::string as key and std::function as value.

map<string,std::function<SuperBase*()>> myMap;

The function return type is SuperBase and the addNewClass function can be defined as

template <typename type>
void addNewClass(std::string name) {
    myMap[name] = []() { return new type();};
  }

So from the main function you can call the function as

addNewClass<A>("A");
addNewClass<B>("B");

Then while iterating you can call the function to get you the desired pointer

 for( auto mapPair : myMap) {
        cout<<mapPair.first<<endl;
        SuperBase * sBase = mapPair.second();
    }

Remember, you need virtual functions in SuperBase to have polymorphic behaviour and then everything should work

Hope it helps