Overloading insertion operator for std::array

March 11, 2022

I’m trying to overload the insertion (<<) operator to output elements of an std::array. The following yields a compilation error:

// overload operator<< to display array objects of any type T and size N
template<typename T, int N>
std::ostream &operator<<(std::ostream &Output, const std::array<T,N> &Arr) {
    for (const auto &Element: Arr)
        Output << Element << " ";
    return Output;
}

But the following works just fine (if I apply it to an array of, say, 5 elements):

// overload operator<< to display array objects of any type T and size 5
template<typename T>
std::ostream &operator<<(std::ostream &Output, const std::array<T,5> &Arr) {
    for (const auto &Element: Arr)
        Output << Element << " ";
    return Output;
}

I’m aware that arrays need to know their size N at compile time, but doesn’t the template provide just that?

The error happens when I try, for instance, the following:

std::array<int,5> MyArr {1, 2, 3, 4, 5};
std::cout << "MyArr = " << MyArr;

>Solution :

The 2nd template argument of std::array is a size_t, not an int.

Also, return output; needs to be return Output; as C++ is case-sensitive.

// overload operator<< to display array objects of any type T and size N
template<typename T, size_t N>
std::ostream &operator<<(std::ostream &Output, const std::array<T,N> &Arr) {
    for (const auto &Element: Arr)
        Output << Element << " ";
    return Output;
}