Getting the number of elements in std::array at compile time

Question

Is the following a valid C++ code, and why not?

std::array a1;
std::array a2;

It doesn\'t compile

Answer 1

array::size() is constexpr, but you can't use it in this way because a1 isn't a constexpr value. Additionally, it can't be constexpr because string isn't a literal type.

However, you can work around this if you want, by deducing the size_t template parameter. Example:

#include 
#include 
#include 
using namespace std;

template
struct array_size;
template
struct array_size > {
    static size_t const size = N;
};

array a1;
array::size> a2;

int main() {
    cout << a2.size() << endl;
}