GCD of multiple parameters

My aim was to generalize the __gcd() available in std <algorithm> header in C++. which should be able to call for a range of values of a std::vector array.

The generalized template __gcd() works perfectly when parameters have been passed directly. Just like below:

math::GCD(1,2,58,54);

However, when I tried to pass a range of values of a vector(the code is given below), it shows the following error:

D:\Programming\C++\CPP Programs\My Test\My Test.cpp|33|error: no match for 'operator<<' (operand types are 'std::ostream {aka std::basic_ostream<char>}' and '__gnu_cxx::__normal_iterator<int*, std::vector<int> >')|

I don't know how to overload operator<< or include an overload function in this template/ program.(assuming that the error is due to overloading of operator<< has missed)

namespace math
{

    template <typename M, typename N>
    constexpr auto GCD(const M& m, const N& n) {
        return __gcd(m, n);
    }

    template <typename M, typename ...Rest>
    constexpr auto GCD(const M& first, const Rest&... rest) {
        return __gcd(first, GCD(rest...));
    }
}

int main()
{
    vector<int> vec={1,2,58,54,102,2,37,13,8};
    for(auto i=0; i<vec.size()-3; ++i)
        cout<<math::GCD(vec.begin()+i, vec.begin()+i+4)<<endl;
    return 0;
}

can anybody help me to overload operator<< or (if it's not the case) to find the error? thanks in advance.

I have done it finally. Thanks for @Incomputable 's last comment. However, I had to make a separation between the new template(for iterators) and the two we had in the question using math name. Just like as follows:

#include <iostream>
#include <vector>

template<typename T64> constexpr  T64 calcGCD(T64 a, T64 b)
{
    return (a==0 && b!=0) ? b: a;
    while(b)
    {
        T64 t = a % b;
        b = a;
        a = t;
    }
    return a;
}

template <typename Iterator> constexpr auto GCD(Iterator first, Iterator last)
{
    auto itrFirst = first;
    auto itrEnd   = last;
    int Size      = std::distance(itrFirst,itrEnd);
    int Result = 0;

    if(Size >=2 )
    {
        int A       = *itrFirst;
        std::advance (itrFirst,1);
        int B       = *itrFirst;

        Result      = calcGCD(A,B);
        std::advance (itrFirst,1);

        for(int i = 2; i<Size; ++i)
        {
            A       = *itrFirst;
            Result  = calcGCD(Result,A);
            std::advance (itrFirst,1);
        }
    }
    else   return *itrFirst;
    return Result;
}

namespace math
{
    template <typename M, typename N>
    constexpr auto GCD(const M& m, const N& n)
    { return calcGCD(m, n); }

    template <typename M, typename ...Rest>
    constexpr auto GCD(const M& first, const Rest&... rest)
    { return calcGCD(first, GCD(rest...));  }
}


int main()
{
    std::vector<int> vec={1,2,58,54,102,2,37,13,8};

    std::cout<<"GCD from Iterator Template     : ";
    for(unsigned int i=0; i<vec.size()-3; ++i)
      std::cout<<GCD(vec.begin()+i, vec.begin()+i+4)<<" ";

    std::cout<<std::endl;

    std::cout<<"GCD from non-iterator Templates: ";
    std::cout<<math::GCD(1,2,58,54)<<" ";
    std::cout<<math::GCD(2,58,54,102)<<" ";
    std::cout<<math::GCD(58,54,102,2)<<" ";
    std::cout<<math::GCD(54,102,2,37)<<" ";
    std::cout<<math::GCD(102,2,37,13)<<" ";
    std::cout<<math::GCD(2,37,13,8)<<" ";   

    return 0;
}

It gives the required output as expected. However, I haven't tested for any other cases.

Out Put:

GCD from Iterator Template     : 1 2 58 54 102 2 
GCD from non-iterator Templates: 1 2 58 54 102 2