The simplest way to ask this question is with some code:
struct Point
{
int x;
int y;
int z;
int* as_pointer() { return &x; } // works
int (&as_array_ref())[3] { return &x; } // does not work
};
as_pointer compiles, as_array_ref does not. A cast seems to be in order but I can't figure out the appropriate syntax. Any ideas?
I find that array types are easier to deal with with a typedef:
typedef int ints[3];
Then your as_array_ref must be written so that &as_array_ref() == &x.
The following syntaxes are possible:
plain C-style cast from int* to ints*:
ints& as_array_ref() { return *( (ints*)(&x) ); }
C++ style reinterpret_cast (suggested by @Mike Seymour - see also his answer). It is often considered a better practice in C++:
ints& as_array_ref() { return *reinterpret_cast<ints*>(&x); }
Cast from int& to ints& which is slightly shorter but (for me) less intuitive:
ints& as_array_ref() { return reinterpret_cast<ints&>(x); }
reinterpret_cast to make it more obvious that something dodgy is happening. C-style casts are both dangerous and difficult to search for.
The cast you need to reinterpret a reference to a variable as a reference to an array is:
reinterpret_cast<int(&)[3]>(x);
Be aware that using this gives undefined behaviour; it will probably work on any sensible implementation, but there's no guarantee that there won't be padding between the members of the class, while arrays are not padded.
I think that what you're trying to do would be easier (and clearer/cleaner) with an union.
xis, in fact, an array of threeints? There's no guarantee that this will work; compilers can add padding between data members in ways that are different from the way that they lay out arrays.