C/C++ value_type

#include <iostream>
#include <vector>
using namespace std;

template<typename T>
typename T::value_type top(const T &c)
{
    if (!c.empty()){
        return c.back();
    }
    else
        return typename T::value_type();
}

int main(){
    vector<int> vec;
    vec.push_back(1);
    vec.push_back(2);
    vec.push_back(3);
    cout << top<vector<int> >(vec) << endl;

3