Question

I am trying to write a function which can take any of the standard containers(list, stack, vector etc) as it’s arguments. I also wish to know the type that is within the container. Here is what I have tried.

#include<iostream>
#include<list>
#include<vector>

template<class data_type, template<class> class container_type>
void type(container_type<data_type>& _container){
        std::cout<<typeid(container_type).name()<<std::endl;
}


int main(){

    std::list<int> list_t;
    std::vector<int> vector_t;
    type(list_t);
    type(vector_t);
}

The type of container_type once inside this function is always _Container_base_aux_alloc_empty which(I think) is a base class of the standard containers.

What is going on here?

How would I make this function return the correct type?

Answer 1

Your code won’t work, because as soon as someone swaps out the allocator or something like that, then you’re done for. You should take any T and use ::value_type, if in C++03, or type deduction in C++0x.

Also, .name() isn’t defined to return anything useful, at all. In any situation. An implementation could return “har har sucker! good luck using this language feature” for every type and be conforming.