Question

Is there any safe and standard compliant way to treat a C style array as an std::array without copying the data into a new std::array?

This clearly doesn’t compile, but is the effect I would like (my real use is more complicated but this short sample should show what I’d like to do). I guess a reinterpret_cast would “work” but probably isn’t safe?

#include <array>

int main()
{
    int data[] = {1, 2, 3, 4, 5};

    // This next line is the important one, treating an existing array as a std::array
    std::array<int, 5>& a = data;
}

It feels like it ought to be possible as the data should be stored identically.

edit: To be clear I don’t want to clear a new std::array, I want to refer to the existing data as one.

Answer 1

You cannot do that. The std::array is an aggregate and holds its own block of data (as opposed to a pointer to a block of data that can be easily reassigned). So there’s no way of avoiding a copy of all the elements. In C++11 this is particularly important because the array’s data cannot be moved, so there’s no efficient std::swap function, for example.