Passing array by reference - subset of a larger array

Question

I know there are other ways of implementing this or using containers. This is just to satisfy my curiosity. Suppose I have the following code:

void byref(int (&a)[5]);

int main()
{
    int a[5];
    byref(a);
}

An advantage of passing a C-style array by reference is that sizeof will work on it, as will std::end. But now it is only possible to pass an array of exactly this size.

Is it possible to pass a subset of a larger array to this function by reference? For example, I'd like to do:

int main()
{
    int a[10];
    byref(a + 1);
}

Is there any way to make this work?

I got it to build and run, giving expected values in VS2015, but of course the code looks very dodgy:

byref(reinterpret_cast<int(&)[5]>(*(a + 1)));

@KarolyHorvath, OP knows that there are other ways of implementing this or using containers. — Andrey Nasonov
– Andrey Nasonov, Commented Oct 24, 2015 at 20:10
In С++ you can use templates: template <std::size_t N> void byref(int (&a)[N]); — Constructor
– Constructor, Commented Oct 24, 2015 at 20:31
@Constructor What if the function only wants to deal with 5 elements? — Neil Kirk
– Neil Kirk, Commented Oct 24, 2015 at 20:47

Andrey Nasonov · Accepted Answer · 2015-10-24 20:30:48Z

1

I have only an idea of wrapping the bad looking cast into a function:

#include <iostream>
#include <cassert>

void byref(int (&a)[5])
{
    std::cout << "Hello!" << std::endl;
}

template <size_t M, class T, size_t N>
T (&subarray(T (&a)[N], size_t start))[M]
{
    assert(start < N && start + M <= N);
    return reinterpret_cast<T(&)[M]>(a[start]);
}

int main()
{
    int a[5], b[8];
    byref(a);
    byref(subarray<5>(subarray<6>(b, 0), 1));
}

answered Oct 24, 2015 at 20:30

Andrey Nasonov

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Comments

gsamaras · Accepted Answer · 2015-10-24 20:33:45Z

0

With this prototype, I fail to see another way to proceed than casting.

Typically, I see this one too: byref((int(&)[5])*(b + 5));, but of course it's the same and less safe than yours.

So, I don't see any clear and pretty way to do it (except for a macro maybe). I will upvote your question however, in order to see if you are missing something here!

answered Oct 24, 2015 at 20:33

gsamaras

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