On Wed, 28 Jun 2006 08:55:11 -0400, David Abrahams <dave@boost-consulting.com> wrote:
Gennaro Prota <gennaro_prota@yahoo.com> writes:
When you write something like, for instance,
COUNT_OF_N(3, x)
though, it's not enough to check that x is an array. It shall be an array, x[0] shall be an array, x[1] and x[2] shall be arrays. I can imagine implementing it with some pp-lib iteration which automatically generates
sizeof(x[0])/sizeof(x[0][0]) sizeof(x[0][0])/sizeof(x[0][0][0]) sizeof(x[0][0][0])/sizeof(x[0][0][0][0])
up to a given limit,
So what's wrong with that?
Nothing. I didn't say it is wrong, just that I can't (still) see an easier template-only approach for the multidimentional case. It would help if you could post your simpler solution. With preprocessing manipulation I agree that you can have one function to detect arrays and do the actual computation with sizeof/sizeof.
but I'm not sure it can *reliably* be done with templates only.
You need a macro anyway, don't you?
You mean for the user? No. My idea was that the macro was provided as a shorthand (or maybe it wasn't provided at all --to be decided) but it was not "needed"; the user could anyway do: sizeof array_count<n>(arr) and that would give the count of the (n+1)-th dimension of arr. That should still be doable with my approach, even with VC6. Just to give the idea, it's enough to add something like this to my previous code: template <std::size_t d, typename t> struct vc6_wrap { static t & expr; enum { n_1 = sizeof(expr)/sizeof(expr[0]) }; enum { s = sizeof(array_counter<n_1> ::on_dim<d>::count(expr).result ) }; static char (&result) [s]; }; // "syntax adapter" template <std::size_t d, typename t> char(&array_count(t& a))[vc6_wrap<d, t>::s]; In my tests so far, this works: int main() { X a[1][2][3][4][5] = { 0 }; char a1[sizeof array_count<0>(a)] = { 0 }; // <-- char a2[sizeof array_count<1>(a)] = { 0 }; char a3[sizeof array_count<2>(a)] = { 0 }; char a4[sizeof array_count<3>(a)] = { 0 }; char a5[sizeof array_count<4>(a)] = { 0 }; std::cout << sizeof(a1) << ", " << sizeof(a2) << ", " << sizeof(a3) << ", " << sizeof(a4) << ", " << sizeof(a5) << '\n'; return 0; } but this doesn't: struct X { operator void*() const; double operator[](std::size_t) const; }; X x; sizeof array_count<0>(x); // no failure :-( --Gennaro.