c++ template to template parameter

Question

recently i was testing some c++ template codes and i found one mind-boggling error. According to my research on internet in particular stackoverflow, this code is completely val

Answer 1

std::vector, the type being passed in as C, has more than one template parameter. It has the usual element type, but also an allocator. The easiest way to get around this while keeping a list of type arguments is to use a variadic template:

template<template<class...> class C, typename... Ts> void print(C<Ts...>& c)
                  ^^^^^^^^                   ^^^^^^             ^^^^^^^^

Actually using the individual type arguments is easier done, in most cases, by explicitly specifying them, as in Cheers' answer. If you don't care about the type arguments, feel free to not keep track of them. In the case of a container, you can even get them from just the container type:

template<typename Container> void print(Container& c) {
    typename Container::value_type t;
}

Answer 2

Expanding on chris' answer, the following compiles fine with both visual c++ 12.0 and g++ 4.7.2:

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

template<template<class, class> class C, class T, class U> void print(C<T, U>& c)
{ (void) c; }

void test() {
    vector<string> v(5, "Yow!");
    print(v);
}

---

However, if you really just want to output the items of a container, why not do this instead:

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

template< class C >
void print( C const& c )
{
    for( auto const& item : c )
    {
        cout << item << endl;
    }
}

auto main() -> int
{
    vector<string> v(5, "Yow!");
    print(v);
}