C++ print template container error (error: ambiguous overload for 'operator<<') understanding?

Question

I want to write template function which can print container like std::vector, std::list.

Below is my function, just overload <<.

Answer 1

Declaring template could be dangerous as this template includes 'all' variable types int, char etc. Due to this compiler does not know which operator<< to use.

In order to take only container type variables use template of templates. Here is working code for you

template class Container>
std::ostream& operator<<(std::ostream& out, const Container>& c) {
    for (auto item : c) {
        out << item << " ";
    } 
    return out;
}

int main()
{
    cout << "Hello world" << endl;
    int arr[] = { 0,3,6,7 };
    vector v(arr, arr+4);
    cout << v << endl;
    return 0;
}